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'95 LeSabre Dies Without Warning

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04-24-2004, 01:17 AM
I have a '95 with 113K. A week ago, I was cruising down the street and the engine died with absolutely no warning. No CE light or code was set. I coasted to the shoulder, stopped, and the car started right back up, and I drove home.

It did this again once each of the next two days, and both times, it started up fine immediately and ran OK.

One of the times, it finally set a P0341 code--camshaft sensor.

I started noticing that you could go just about five miles after the engine was first started from cold (in the morning, or leaving work) before it would happen.

Then yesterday, it *didn't* start right back up like usual. It would crank, but not fire. I could hear the fuel pump energize with the ignition in the ON position. Battery connections looked clean and were snug. I left it on the side of the road for an hour while I went to get a camshaft sensor. When I got back, I tried starting it, and it did. (engine cooled down?) I got about another 5 miles, and dead it went. I put the camshaft sensor in then--took about 10 min.--and it started right up. I was pretty happy, thinking I'd fixed it.

Wrong. Next morning on the way to work--about 5 miles out, dead--wouldn't start. An hour later or so, it started up and ran another 3-5 miles over the the mechanic I took it to out of frustration.

He put it on his Sun diagnostic machine all afternoon and it didn't die once.

I'm wondering if I don't need to be looking for an intermittent open circuit in the wiring between the cam sensor and the ECM somewhere--maybe that's why I get it driving down the road (a major source of vibration in my county) and my tech doesn't with it idling in his bay.

I would also *like* to think that the 341 isn't a "false code" due to the engine dying for some other reason.

04-24-2004, 04:32 PM
PCM? What is that exactly?
(You don't mean ECM - Engine Control Module - do you?)

04-27-2004, 10:19 PM
Well, it turned out to be the ignition control module under the three coil packs on the engine. The part (AC Delco #1977A) was about $140, and with 2 hours labor the bill ran just short of $300. (ouch) I'm a bit hacked that the 341 code was false and I sunk another $40 into a cam sensor I didn't need--chalk that up to experience, and probably worth it. But I guess the way I have to look at it is as if I were just making a car payment this month where I usually don't have to.

I got to looking on eBay to see what the going rates are for these modules. They had a few listed, and some of the bids were starting down around $40 for new ones! My local big-name auto parts store wants $200. So I'm thinking for that $40 price I may pick one up off eBay or at the salvage yard and throw it at my '90 LeSabre--it was doing a similar thing, dying with no warning. (Although I still wonder if there's some overheating thing going on there...)

Found out too that Snap-On and maybe other companies make "load testers" for these modules, and I'm thinking about looking into what those cost. The ones I've seen so far look like they'll do about any brand of car, and if it were less than $100, it could pay for itself the first time you used it.

06-03-2004, 08:12 PM
No, I spoke too soon. This problem was not fixed by putting on a new ignition control module. A couple weeks after the ICM was replaced, it started doing exactly the same thing. I took it back to the same shop, and this time they put a camshaft sensor on it (yes, after I had written down for them that I'd already done that to no avail). When I found this out, I said I didn't think the car was fixed, and we took it on a quick test drive, and my statement was proven when it acted up again. (Also found out that a bad cam sensor won't kill a running engine--it'll make it hard to start, but it won't kill it. So why they put a cam sensor on it, I don't know. I sure wouldn't have put mine on if I'd known that fact.) At any rate, they had the car in their shop for two weeks monitoring, probing, checking, etc., and got it to fail once, but didn't capture the data for some reason. They had a portable monitor on the crank sensor outputs, and I drove it for them and it didn't act up. So I took the car back home because it seemed like we weren't making any diagnostic progress, and on the very first run to work today, bam. Engine died about 5-6 miles from the house. Tried to start it right away, and it wouldn't. I waited a minute or two, and tried again. It fired right up, and I drove it the remaining 10 miles to work. Crapped out just like that again on the way home tonight. I'm not 100% certain, but tonight when I turned the ignition back on to restart it, I don't believe I heard the fuel pump whirr. After 30 more seconds, I tried again, and it did whirr, and it started. So I'm wondering now if I have a fuel system problem, and I want to replace the fuel pump relay. Trouble is, I haven't found it yet. It's not one of the six relays in the "Maxifuse / Relay Center" on the firewall. By the way, crappy job of labeling the relay functions there, GM!! What's more fun than pulling relays out one by one and checking to see which function doesn't work? But I guess we can't afford a 5-cent label on a $20,000 car, huh?

I'm thinking it's buried in a smaller relay center under the right-side sound insulator--anyone know for sure?

I don't think it's a bad fuel pump so far because I had chronic fuel pump problems on my '89 LeSabre, and when it overheated, it always needed way more than a minute or two to come back and work (like 1-2 hours or more) and finally, it just quit coming back altogether. This one doesn't act that way. After all the hide-and-seek hassle this problem has been, I'd gladly pony up the dough right now for a new OEM fuel pump if that would fix it!! I guess I could rule out the fuel pump itself by taking a jumper wire with me, and the next time it dies and won't start back up, jump that green-tabbed fuel pump test connector to the battery and see if I can start it then. If not, fuel pump. If so, it's something causing the power to the fuel pump to be cut. I guess that is unless the relay is included in the test circuit too. (??)

In the "diagnose fuel system" section, my Haynes manual says that there's a possibility the oil pressure switch could be bad. But it doesn't give any info about where that switch is or how it's wired into the fuel pump / pump relay circuit. Anybody know? So after the fuel pump relay gets ruled out, I'm going to focus on that switch next. I would note that I'm not getting any oil pressure lights on the dash at any time.

This ever happen to anyone? Any help wouuld be appreciated.

06-04-2004, 08:02 AM
That green tabbed connector goes directly to the fuel pump (bypasses the relay and oilswitch). If you put a 12v test lamp between it and ground, it lights when the fuel pump is getting voltage, thereby checking the relay (and oilswitch if present). I am guessing crank sensor. Its kind of hard to test when it is intermittent. My microfiche for 87 says put a timing light on a sparkplug and crank it. If the crank sensor is working, the timing light flashes, if not it could be the crank sensor (among other things). Maybe you can figure out how to drive it around with the timing light attached till it dies on you and then quickly see if the timing light flashes when you are cranking it.

06-05-2004, 01:42 AM
that sounds totally familiar. ive got a 94 and about 120k it started acting up like that, and they've had to replace a number of my computer components. have them check your Ignition Moduel, crank shaft sensor, and maybe even the Main Computer. i took it to Firestone, and they were able to help me out quite a bit

06-06-2004, 03:06 PM
just fixed my 96 lesabre. same prob. there is an 8 way connector in front pass side rail underneath carpet. If car ever in a flood or spill water in pass front carpet, connector corrodes. controls fuel pump,pw, and power seat. clean, apply grease, wrap with tape.
I spent 1500 on fuel pumps,relays,etc, all for naught.
Goodyear and Firestone don't know squat!

06-07-2004, 07:04 PM
Again, I've already had the ignition control module replaced. (Not that it means that it's guaranteed to be good--but as soon as it acted up again, I took it right back to the shop that installed it, and after another two weeks, they still didn't have it figured out.) It's funny...everybody I talk to about it says "it's going to be something simple." That may be true, but it's apparently not *that* obvious. I have yet to meet the person that can tame this car. Wonder what's in the Yellow Pages under "Exorcists"...

Interesting suggestion you made there, tdenkler. I don't believe this car's ever been in a flood, and I don't think I've ever had the carpet get wet except for a few hours about 10 months ago when I shampooed it. But that might be worth looking at.

By "rail" are you talking about that plastic trim piece that covers the edge of the carpet alongside the door jamb where you step in and out of the car?

By the way, here's the latest in my almost 2-month saga:

Put a fuel filter on it yesterday, and drove it 18 mi. w/o idling first, and it didn't die at all. Got my hopes up just a little, but had them dashed again this morning. 8 miles after leaving the house, bam. Took about 3 minutes to get it started again. Crank, wait. Crank wait. Repeat. Sounded like the fuel pump was priming each time, too.

I noticed that the vacuum hose going to the fuel pressure regulator is pretty rough looking--has some cracks. So I'm going to replace that next.

I don't see how any of this explains why it won't die if you just idle it for 10-15 min. before you decide to drive it any distance. If you don't idle first, it's certain to die (or has every time thus far).

I saw in the Park Avenue forum where somebody was grousing about GM's cheaper rubber on their vac hoses, and another person took issue with that criticism, saying that even at 4 cents' savings per car, that it adds up to real money when you build a lot of cars. May be, but even if they built a million units on one particular model in one year, 4 cents would be a savings to GM of $40,000. Wow. That's a piddly drop in the bucket to GM, and any warranty claims arising from that cost-cutting move will eat into that. 10 times that would be a piddly drop in the bucket, too. Cutting corners on design and materials is something I can be more forgiving on when I buy a Yugo or the low-end GM model or whatever. When you drop $20K+ on a nicer car, though, those kinds of cost cutting strategies seem a lot less acceptable. I work for a major OEM (not cars), and I see this cost-cutting (we call it "value improvement") stuff every day, and when the customer inevitably gets left in the lurch, my phone rings. We have a very expensive machine down because we "saved" 10 cents by going to a cheaper electrical terminal design. In an industry where downtime can be very costly. Not smart. Just one warrany claim blows away all the yearly savings the bean counters claimed we'd reap, plus more. It's like OEMs today have completely forgotten that reliability, not just cost, is a selling point. Reliability is a force for developing longstanding customer loyalty. Companies today are in it for the quick kill--how do we make the shareholders happy today. What about tomorrow's shareholders, people? And tomorrow's employees?

[Now stepping off soapbox...sorry. I will try to remember this is not the op-ed section.]

Jed Rule
06-07-2004, 09:57 PM
Tim, I agree with you completely.
What is GM thinking when they charge $300 for a plastic upper intake manifold that cannot withstand the heat of the EGR. Didn't any of those engineers ever burn their fingers on a EGR valve? Have they even opened a hood? Then when your warantee is up they come up with a $$$$ replacement of both the upper and lower manifolds. It takes two guys in Canada to design an effective repair.
Back to your problem:
When the ign is turned on the PCM energizes the fuel pump relay which powers the circuit to the fuel pump. It will remain on as long as the engine is cranking or running and the PCM is receiving fuel control pulses from the ignition control module. The fuel pump relay is #N in the relay center to the right of the glove box. You can apply 12v to the test connector to by-pass the relay and PCM control circuit. Did you try to spray some carb cleaner in the throttle when it won't restart? That would tell you if it's a fuel delivery problem. You will need to test the fuel pressure too. Also check for gas in the vacume line to the fuel pressure regulator.
If you remove the fuel pump relay while the engine is running it should continue to run. If it dies you have a bad oil pressure switch.
I don't understand why it doesn't set the check engine lite. You could have a bad PCM or poor connections to the PCM Check the PCM grounds on the back of the engine next to the oil pressure switch (under the #2 spark plug). Good luck.

06-08-2004, 08:33 PM
Latest update: New vacuum hose did nothing. Not real surprising, but one more thing ruled out. It died once on the way to work this morning; I wasn't hearing the fuel pump prime every time when I turned the key to the on position. So I thought I might be on to something. Got it started and went on to work. Then tonight, I didn't want it dying on the way home, so I idled it in the lot for 20 min. I came back out, and for the first time in two months, it finally had died idling!! So that's new info. Couldn't start it back up, and again, the fuel pump didn't always make a noise when I turned the key to the "on" position. Got my fuel pressure gauge out, but I never saw the pressure below 40 psi at any time. So that's making me think now that maybe the fuel side is OK after all, even though I don't understand why sometimes the pump makes noise and other times it doesn't. At that point, it still wouldn't start, so I poured 12 oz. of cold water on the crank sensor (that's a trick I've seen other people write about here in the forum, so I figured "why not?"). That didn't have any immediate effect. After a few more minutes and a few more crank attempts, it started back up, and I got about 4 miles with it before it died again. Another five minute delay and I got it to go and made it back to the house. Is it possible the ignition switch itself is bad and causing the engine to die? I'd think that if the ignition switch were bad, you wouldn't even be able to get it to crank. And it's always at least cranked after it died.

I already bought a fuel pump relay, so I'm going to try to put that in tonight and see what happens tomorrow, even though after today's events I'm again a bit skeptical that I'm dealing with a fuel problem.

06-08-2004, 09:37 PM
Replace the ECM. My 94 had a similar problem, and I went through the same thing you did. Fuel pump, filter, relay, plugs, wires, ign module. Replaced the ECM and all was fine. You can pick up a reman ECM for about $150 Hope this helps

06-09-2004, 07:07 AM
If you put a 12 v lamp (or voltmeter) between the green tabbed fuel pump test connector and ground, it lights when the fuelpump is receiving a signal to run. If the bulb lights when it is supposed to, that eliminates the fuel circuit. (ie the fuel relay is receiving an "on" signal from the ECM, and the relay is working and the wiring to the pump is OK)

06-09-2004, 06:39 PM
Thanks for the tips, LeSabrelover and rustbucket.

The plan today was to carry my buddy's timing light along for the ride to work, and when the car crapped out, to use it to decide whether there's any spark there when it cranks but doesn't start.
The idea being to confirm whether the problem is on the fuel or spark side.

Well, so much for plans. It rained all day today, and the car didn't foul up to or from work, nor during an hour of idling once I got to work. It's like the car knows it's being watched. Who knows, maybe the humidity plays a role in the problem somehow.

Hopefully it will fail tomorrow and I will have more to report. I'm starting to like this new ECM idea more and more, I have to admit.

06-10-2004, 10:46 PM
It failed twice today. Both times I got the timing light on it almost immediately after the car stopped rolling, and both times it started immediately when I cranked it. So didn't learn much there. I may have to rig the timing light up so it's attached all the time and the gremlin won't have a chance to escape while I jump out, pop the hood and clip the light on.

Priced ECMs today. Salvage yard has 'em for $75, but no warranty. The two name-brand parts outlets here in my little burg both sell 'em for $110 after core. One offers "lifetime warranty," and the other 90 days. It's getting awfully tempting to go get one and try it, as much as I hate throwing parts at cars. I will check the (+) and ground wiring from the battery back as I saw suggested on another thread in this forum.

I think it is past time to get the real factory service manuals, too, so I can figure out what wires go where.

06-11-2004, 12:23 AM
Just one quick thought, if the car is really quitting almost instantly and not chugging or hesitating otherwise, it probably isn't a mechanical failure meaning an air/fuel delivery problem. How did you find out that you set a cam sensor code that first time? Do you have your own scan tool? The reason I ask is because the CE lamp doesn't come on for every failure, and you may have stored codes in the computer that you don't know about right now. If I had to put all of my money on something, I would definately bet on the PCM ground connections. Oh by the way, GM refers to what is normally called the ECM as the PCM or (Powertrain Control Module), they do this in all of their shop manuals. But since the ECM/PCM works by switching grounds, its absolutely critical that the ground connection is stable and solid, try filing the connections down and replacing any bolts that are holding the ring connectors in place. You can easily trace PCM wires using their color coded insulation, and of course solid black is always a ground, so trace those back first and check the connections. As im sure you know even if the connector is firmly held in place against a metal part for a ground, this doesn't mean that corrosion between the connector and the metal part isn't destroying the flow of electricity. Use a good metal file to clean all of your PCM connectors. Now on my older 1992 LeSabre there was a ground that ran directly off of the big ground terminal on the battery, it was a little say 16 or 14 gage wire that split off right at the battery terminal and went straight to the PCM. But GM put a connector in that line about 12 inches back from the battery so that the battery cable could be easily replaced without having to splice that line. That connector rotted out on my car and caused almost exactly teh same symptoms you are describing, until finally one day I started getting all kinds of crazy lights on teh dash board including ABS and Security indicators. Basically the PCM wasn't getting enough clean power to operate.

06-12-2004, 09:32 PM
Yesterday I got the timing light on it after it died. When I cranked, no light.

Dug the ECM / PCM out of it tonight. I checked the ground wiring there near the battery where it attaches to the frame. It does look pretty cruddy. There are three black wires that are under that nut. The nut and top ring terminal are rusty-colored, but snug. I'll clean that up tomorrow and maybe take it for a drive. I have one of the two main connectors detached at the firewall - maybe I can check resistance to ground from that connector before doing any cleaning. If it's more than a couple tenths of an ohm, that'd be abnormal in my opinion.

Found the fuel pump relay, too. After I clean the ground post up and if need be, try another ECM, then I will pop a new fuel pump relay in there while all the guts are exposed (though I doubt it's fuel-related at this point). As impatient as I'm getting with this, I still don't want to try more than one thing at a time so if/when I do actually fix it, I'll know what it was.

To answer pcmos' question, I read the codes out w/my brother-in-law's "X-Ray" scan tool. ($$, so I hear) Can't just stick a paper-clip in the ALDL connector like the older cars. The only code we've ever read out is P0341 - camshaft sensor circuit. It doesn't always set a code when it dies. It doesn't always turn the check engine light on either. So that code was what led me to camshaft sensor replacement early on in this ordeal. I feel foolish for blindly reacting to the code. (But not quite as foolish after professional mechanics did the same thing later--in their defense, their electronics guy was on vacation, and to their credit, they didn't charge me for it...) I hate "false codes." As complex as these controllers are nowadays, there's bound to be some occasions where they lie. I think the 341 sets because of the engine stopping, instead of the engine stopping because of the 341 code.

Could it be that the ECM is losing power / ground, the engine dies, and then the ECM wakes back up sometimes (because of this bad ground theory or because the ECM *is* whacked), and because the engine is dead at that point the ECM doesn't see the cam position in the right place like it expects it to, and therefore the 341? And maybe likewise, on those times the ECM *doesn't* wake right back up, those are the times it doesn't turn the CE light on and set the 341?

ECM / PCM P/N for this car is 16183247.

More news as it breaks. (News, not the car.)

06-13-2004, 12:03 PM
I do not see anything about replacing a crank sensor. Next time the vehicle stalls, have a gallon or two of water in the trunk, pour it around the crank sensor, located next to the crank shaft pulley. If the vehicle starts immediately, replace the crank sensor.
Good Luck.

06-13-2004, 03:37 PM
pcv: I did try the "crank sensor cool-down" thing. (See post #12, 6/8/04) I didn't use as much water as you suggest, admittedly, so maybe I didn't give it a fair chance to work. You probably know of it, but I saw in another forum where a guy was suggesting to someone else to use their windshield wiper fluid pump to put the water on the sensor as you're going down the road. He put some extra hose on the outlet, duct-taped the hose in place, filled the reservoir with ice water, and drove down the road. When the car would start running rough, he'd hit the wiper spray switch, and if it cleaned up the rough running, he knew he needed a new crank sensor. I thought that was a pretty cool diagnostic method, though it seems out of the ordinary.

So far today, I have checked my grounds - didn't find anything I'd consider high resistance, but I thoroughly cleaned the ground post on the frame next to the battery and all four ring terminals that come off it. Those babies shine. Haven't got a new ECM / PCM yet - I put the original on the RH floorboard and hooked it back up. It's sitting outside idling. If it dies, I will get a new one and install it.

One thing I noticed...maybe it's not significant, maybe it is: the oil pressure indicator moves around at idle. It will sit at 50 psi for a couple seconds, then it will wiggle between 50 and 60 psi for a couple seconds, then drop back to 50 or so. It seems erratic. For all I know, it's normal.
This fluctuation smooths out when I drive the car.

Maybe cleaning up the ground is all the ECM needs to do its job. Got my fingers crossed. I will go change the oil in the other car while I wait to see if this one dies again.

06-14-2004, 09:27 PM
I am not totally convinced it's fixed just yet, but:

Yesterday after cleaning the ground terminals up, it idled for five hours straight, and I then drove it 25 miles, and no failure.

And today it got me to work and back--no failures.

I will be fairly convinced if it goes the rest of the week. It hasn't logged even two good days in a row in two months.

06-14-2004, 09:38 PM
Yeah I was actually the one that posted that message on the other thread about using the windshield washer pump to get some cool water on the sensor. Actually I was talking more about using this method for diagnosing a bad cam shaft position sensor, not the crank sensor, just because the crank sensor is monitored more carefully by the PCM. Usually even intermittant failures on the crank sensor will trip a code in the computer, but the cam sensor is not monitored as carefully. I actually was able to diagnose my cam sensor on my old 92' LeSabre by using the washer pump to dump some cold water on it while driving, but this is because when it was acting up in the driveway one night I poured some cool water down behind the pulley's and got the car to run. Since there are a couple of sensors that were hit with the cold water, I decided to rig up the washer pump to get it more specific, and also to use it and drive the car at the same time so I could be sure. First time it started acting up, I gave it a quick shot, and boom, the car started running perfectly normally within a quick moment. This was enough to convince me to take a gamble at replacing the cam sensor and I never had a problem again.

06-15-2004, 07:04 AM
Sounds good so far. In case get back in the parts replacement mode, Under 400 RPM(that is when cranking) the spark is controlled by the crank sensor, the cam sensor and the ICM alone.(not the ECM). Above 400 the ICM tells the ECM to take over the spark, and the ECM tells the ICM when to spark.

06-15-2004, 11:57 AM
Yes, and if you read the manual you will see that after cranking and above that 400 RPM mark, the PCM monitors the presence of a signal from the cam sensor, but it will only set a code if that signal is gone for a full 5 seconds. This is the loop hole in GM's code that allows the cam sensor to fail in an intermittant manner without setting a trouble code. The other problem is that the cam sensor produces a simple on-off series of pulses, and unlike the crank sensor, the PCM doesn't compare this signal to a known reasonable signal. So if the sensor misses a pulse or two every few cycles of the engine, the computer will still try to use the reading anyway, which is what caused the driveability problems on my old 92'. I can only assume that the computer was using the faulty signal. I suspect this because if the computer were generating a random cam signal to use, it would only get it right about 1/6 of the time regardless of engine RPM, it would run terribly at all RPM's in this case and I can't imagine that the computer could be doing this for more than 5 seconds and not count that as a loss of signal from the cam sensor. Since no code ever set, and since the engine was having trouble only at higher RPM's, I made the assumption that the PCM was actually trying to use a poor or intermittant cam signal. As the engine RPM's increased the percentage of bad pulses in a given time period increased and the problem became noticable, but at lower RPM's the cam sensor didn't have to get so many pulses correct in the same period of time because the engine and sensor magnet weren't turning as fast. One way or another, however, replacing the cam sensor most definately fixed the problem, and my gas milage went back up to like 25mph highway.

06-15-2004, 12:02 PM
I'm sorry, I don't mean to blab about the cam sensor, I just realized that this is completely off topic in this post. But I am curious to know how this problem turns out with the "95 LeSabre dying without warning". This really doesn't sound like a cam or crank sensor problem to me at all, just because of how quickly it dies out. Sounds more like a power distribution / ground problem, but it will be interesting to see if cleaning those terminals helped out.

06-15-2004, 08:05 PM
No apologies needed as far as I'm concerned, pcmos. I'm glad to learn all the extra details. I know some people get frustrated if they have to read more than a couple lines, but without the details, what's the point of even sharing a forum, I figure.

Now I must say that rustbucket has me worried again with what was said in Post #23 about the PCM having nothing to do with spark control during cranking.

The ICM *was* replaced about a month ago by my local shop in their first effort to fix this problem. I guess there's nothing that says that I couldn't have gotten a bad replacement. But I'd have thought my mechanic would have immediately load-checked the one he installed after I brought it right back in complaining of the same symptoms he originally told me were cured by replacing the ICM on my prior visit. He seemed awfully sure the original ICM was bad. Yet after I took the car home from the shop with the problem unresolved, the symptoms continued through last Friday. If the original diagnosis of a bad ICM was *truly correct*, I wonder why the shop didn't say the replacement ICM was bad too and that I needed another one?

Here I'm thinking I have it narrowed down to the PCM or its ground, but based on what rustbucket says, how can the PCM be at fault when it dies and won't start back up right away? It seems reasonable to me that if the PCM didn't have a stable ground it could cause the engine to die, but if the engine doesn't even *need* the PCM to start, how does it add up that the PCM and its ground should be suspect at all? If I unhooked the PCM and put it in the back seat, could the car still be started?

By the way, no failures again today. That makes two straight work days, plus almost 6 hrs engine time on Sunday. This streak is unprecedented. The last thing I did was clean up the frame ground post and ground terminals. Yet I do not dare claim victory prematurely.

06-15-2004, 09:09 PM
Well, let me double check my shop manual for my 1992 and my 2000 LeSabre's and make sure I am correct on this. But I believe the PCM unit is required to initiate the startup sequence. I am pretty sure that it is the job of the PCM to turn the control over to the ICM before it even fires the first spark, and it may also be the case that the PCM is designed to take a few moments to reset if it senses a bad power supply. Once again I will double check this later, but I am also pretty sure that there is a ground post for the ICM module itself under the alternator, which you may want to clean up as well. Frankly I think you got it fixed by cleaning those PCM grounds, but one must be cautiously optimistic in this tricky business.

06-16-2004, 07:32 AM
I said the ECM does not control the "SPARK" below 400 RPM. It still controls the fuel injectors and probably the ICM gets the supply voltage through the PCM in some way. So it couldnt START without the ECM working, but the timing light should still flash (of course if all the power and grounds were right). When your timing light test did not work, that leads me to the cam sensor, crank sensor and the ICM, but not the ECM. (again assuming all the connections were good)

I just did a test on my Lesabre. I unplugged the ECM at the battery, and put on the timing light, and cranked it, and the timing light was flashing. (I was wondering if what the manual told me was correct!)

06-16-2004, 06:50 PM
When I used the timing light during cranking last week, I got no flashing. So maybe this thing is caused not by loss of the PCM/ECM's ground, but possibly by the loss of the ICM's ground? I cleaned four ground terminals on the one fender-mounted post--maybe one of them *was* for the ICM, I'm not sure. I did not realize the ICM ground might be under the alternator, nor have I checked anything under there. If that's where it is on *my* car, then the ICM ground has not been messed with at any point in this story.

If it's an ICM or ICM ground thing, I don't see how the car can possibly be truly fixed at this point. Based on rustbucket's test (very cool of you to do that and share the results, by the way), if you can unplug the ECM/PCM altogether and still get a spark during crank, then it sounds like a non-functional ECM/PCM could *not* have been the cause of my missing spark.

Only thing I can figure is that even though I might not have realized it, the ICM ground does run to the fender post and I actually did clean it.

So I'm still confused: *IF* it's really fixed (and that remains to be seen), then what explanation allows *all* the facts in the case to fit together and not contradict one another? Guess I need to know just exactly where all four of those grounds actually go...

I don't want to drive anyone crazy with all my questions and handwringing, but I sure would like to be able to go back to the shop and explain to them exactly why this happened and what fixed it and be able to back it up.

No failures today either. Cautious optimism is the status.

06-16-2004, 09:20 PM
I am a student at Nascar Technical Instutite, I have a 1987 Buick LeSabre with the same problem and I have been informed that the most likely cause is the Crankshaft Position Sensor (CKP), this is what produces the signal to the ICM which controls the ignition and may not produce a good signal if it is dirty or misadjusted. The Camshaft Position Sensor (CMP) will just make the car back fire and lower fuel econmy because it only controls the sequential fuel injection. I have not put a new CKP in it yet because I was just informed of this today. But i'am going to put a new one in tomorrow and let you know how it works. If you find anything else please let us know.


P.S. There are no TSB (Technical Service Bullitins) from AllData on this problem.

06-16-2004, 11:45 PM
During the recent two weeks that my car was in the shop, the technicians had put a portable two-channel graphic-readout meter on both of the crankshaft sensor outputs. Both signals were clean, at least during any time they were being monitored. At no point have I seen any crankshaft sensor-related codes, though that may not mean much one way or the other. I do have a known-good crankshaft sensor left over from a diagnostic effort on my old/sold '89, so if it comes to that, I could put it on for little or no additional cost as long as the same sensor works for a '95. I don't enjoy taking that pulley off to access the sensor, though.

06-17-2004, 01:22 AM
Well lets assume that something you did under the hood either fixed the problem or improved it, or changed its behavior (being cautiously optimistic). I went onto ebay and found some pictures of 1995 LeSabre's for sale. Lots of people take pictures of their engine when they place a car for sale on ebay, so I got a good look at the engine compartment in a couple of different 95's. From what I can see in the picture, the layout looks identical to my 1992. I think there is a good chance that as long as you do not have the series II version of the 3800 that the wiring would be the same under the hood at least. Ok, so in order to follow a diagnostic process here, I need to assume that the ground distribution is the same on your car as the way it is described in my manual for my 92. I remember working on the ground post on the fender as part of my sweeping goal to clean ALL of the ground posts so that I could completely eliminate a ground problem. Technically speaking a faulty ground could cause an interruption in another circuit that would lead to a cascading failure. Although this is not likely I made the diagnostic assumption when I worked on mine that it would be possible, hence the idea of cleaning literally all under-hood grounds.
Now to start with, it is important to note that ALL grounds, literally everything that is grounded on the car depends on the negative battery terminal making contact. This car WILL NOT operate at all without the battery connected, which means all power is derived from battery power, and even if the ground on the alternator is perfect but the ground on the battery terminal connector is bad, you'll have a problem. That said, lets move to the "fender ground" which is referred to as G103 in my shop manual, G103 is actually fed by one single wire that jumps over to the fender from G104. G104 is located under the coil pack in that general vicinity (poor diagram), but I remember working on both G104 and G103 on my LeSabre. So basically there is another bolt sticking out under or around the bottom of the coil pack just like the bolt you cleaned up on the fender which has a ground connector on it and a little nut to hold it on, called G104. There is one right next to G104 with a bunch of terminals, but I’ll get to that in a minute. One of the connectors on G104 is just a wire that jumps right over to G103 on the fender. Now if my memory and my manual serve me right, the other connector on G104 is the main battery cable from the negative terminal on the battery. Please let me know what you find when you trace that big fat black cable from the battery, I really think it connects to a ground post under the coil pack. G103 feeds ground to a bunch of unrelated accessories including turn lamps and the horn and that’s all. So I highly doubt that anything you did to the ground terminal on the fender affected the problem that you have. I hope I didn't mislead you earlier on that one particular terminal, but I wanted to stress the importance of cleaning all of them :)
As for the rest, G100 is home to a bunch of different grounds including all of the ones for PCM related components including the PCM itself and the cruise module. Now I remember almost perfectly I was able to find this one under the coil pack, I know this because I was stupid enough to cut off a bunch of the terminals to replace them before I realized I was all out of new terminals to crimp on. So I had to twist all the wires together and limp the car down to my electronics store to buy new ones. This ground post is the most important and is located under the coil pack. You'll know this one from G104 because it will have a bunch of terminals on it. I would definitely make sure you clean this up.
G102 is under the driver’s side fender and feeds a lot of different accessories that aren't relevant. It also supplies ground to the electronic level control system if you have this, and some of the electronic controls for the brakes, but nothing that should bring down the car in the event of a bad connection.
Now the second wire that splits off of the battery on the negative terminal, which is a thin spaghetti looking wire compared to the heavy main ground line, is also important. This wire feeds a number of electronic control modules, including all of the grounds for the air bag system and the ABS system. So you want to make sure that the connector you looked at is making a really good connection, I actually cut the connector out and soldered a new one in because I didn't trust the quality of the terminals inside based on what the outside of it looked like.
Ok, so this is long reply I know, but I hope it helps you narrow down the source of the problem. The thing about it is, if you played with that battery terminal at all or any of the main connections from there to the engine this could be what caused the improvement. Not only that, but we haven’t even gotten into the positive side of things yet, and any terminals that you cleaned or repaired or even just unplugged and plugged back in could have fixed the problem. But to be sure I would definitely hunt down that ground post under the coil pack to clean all of those connectors as well. As I remember on my old 92' if your newer one looks the same, G100 is in a dark crevice behind a metal plate, but once you find it, it is fairly obvious from that point forward. I remember having to work around the accessory belt while I was trying to tighten the nut back on the post with my ratchet, so that should give you some idea of where this is.
Most importantly, however, I am really curious to know exactly what things you cleaned or re-connected that were related to the power distribution under your hood. I really think you must have done something else to cause this change in behavior, other than just cleaning the G103 post on the fender. Either that, or your ’95 model is wired differently from my older ’92. Maybe you can shed some more light on exactly what you altered or changed under there.

06-17-2004, 10:22 AM
What style of ignition do you have? My LeSabre has type two ignition,with three two post coils. I tried to clean the grounds on the motor last night and had no luck. I will look on alldata today for all ground locations ralatedtothe ignition system.

06-17-2004, 06:52 PM
Whoa, pcmos - you've got me bummin' a bit. But I do appreciate your sticking to the straight facts like that. I will see about posting more details on where the grounds actually go on my car. It will be a minute before I digest the contents of your last post...

The only other things I've done other than cleaning the ground post on the RH fender are:
1) Disconnect that big multi-way rectangular connector on the firewall, inspect it, and reattach it
2) Take the ECM out of its clip and set it out on the RH floorboard where I have easy access to it--it's been riding there all week. (Maybe that's somehow significant.) At some point, that box will be going back up under the dash--if the problem comes back, that'd be a hint.
3) Disconnect and reconnect the battery ground cable; this was so I could probe around and disconnect things without causing problems.
4) Feel around / examine underhood wire harnesses in general.

It just seems highly unlikely to me that any of those things could have amounted to a fix.

BReynolds: I have the three round two-post coil packs.

No failures again today. Makes me wonder if I wouldn't be better off just leaving everything under the hood alone--it's been getting me down the road, and that's the main thing.

06-17-2004, 07:45 PM
Went out and took another look. Mine's not a Series II engine--not if you go by the molded plastic engine cover, anyway.

I found this "G104" post under the coil pack / ICM mounting plate. There's only one wire coming off it--a big fat black one that goes straight to the battery ground. The wire that jumps over to G103 on the fender where I did my cleaning doesn't come directly from the G104 point in my car. It comes out of the back of the molded connector on the battery ground. All three of the wires that are fastened the G103 fender post drop straight down into a conduit that runs along the RH fender. This conduit also runs forward to the headlight and turn signals on that side. But these three ground wires (two thicker ones, one thin one; all three thinner than the wire that came over from the battery) run back to the firewall and go down into the dash. I'm not sure which of the two firewall wiring ports they run to--didn't want to dig in that far just now, but at any rate they do go through the dash.

This "G100" I never did see. I looked all over under the coil pack, and there's just nothing there but the fat black wire that runs to the battery. There are a couple of conduits running through under there; one is carrying the wires that go to the ICM connector. And there is an odd "squash-shaped" thin metal plate there that holds those conduits away from the belt, but I can't see any wires coming out of the conduits anywhere along there.

Could it be that on my car the G100 ground really does come off the fender ground too?

06-17-2004, 08:00 PM
I believe that squash shaped metal plate is what hides the G100 post, if it is like mine i think there are two nuts or so that hold the plate onto the engine and then when you pull that off you'll find the G100 down in there. It may be worth checking, but I understand why you are reluctant to mess with it. As I remember it wasn't too big of a deal to take that plate on and off, its just a matter of squeezing the tools in there. If G100 doesn't exist under that plate then it may be the case that the fender post also contained the PCM ground and you may have fixed it. You can always pull that fender post off and try to start the car :). If the connection to the fender was bad, then it should render the same affect as simply removing the connectors from the post and starting the engine without it. If this only affects some accessories, but the engine runs normally without any serious lights coming on at the dash, then you're probably overlooking the PCM ground somewhere. One last interesting experiment. Try loosening the bolt that holds your negative cable onto the battery terminal, just enough so that it will wiggle easily on there, then go into your car and start it up (if the cable isn't too loose). Once you have the car running, go outside and just wiggle that cable on the battery terminal, I know for a fact that you can reproduce your symptoms this way, because this is what I did to find the problem with mine. You'll wiggle it back and a couple of times and the engine will die instantly.

06-18-2004, 12:37 PM
A-HA! Knew it was too good to be true. Today on the way home from work, the engine "glitched." I say "glitched," because it didn't actually die, or didn't die long enough for me to notice that it did. The little round red LED lights near all the dash gauges came on for a brief instant, and the RPM gauge when up to around 4000 wildly (though I don't think the engine really went that high--I was driving at about 60 mph, 2000 RPM when it happened). The check engine light did come on and stay on after this happened. I will have to pull the code(s) and see what that's about. (I predict another P0341.) This is only the second time the problem has happened where the engine kept going instead of dying altogether.

So now...did I "undo" something from fishing around last night looking at grounds again? Has the past several days of trouble-free driving just been a fluke? Is the ECM happier lying on the floorboard than being stuck under the dash? Hmm...

When I got home, I wiggled all the wires at the ECM connectors and tapped it here and there (gently); that didn't cause a problem. I popped the hood and wiggled the ground wires around near the fender ground post, and also the wires that run into the ICM; again, no problem.

What do we make of that RPM gauge going wacko like that? Now I'm *really* thinking I need to get a new ECM.

06-18-2004, 05:24 PM
Replace the ECM. That's EXACTLY what my 94 did when the ECM died on it.

06-20-2004, 11:13 PM
I replacedthecrank position sensor andIhave had no problems yet. I did not have to remove the harmonic balancer, it actually made it easier to align the new sensor with the sensor wheel on the back of the balancer.

06-21-2004, 07:09 AM
Probably the ECM is using the sensor inputs (either crank or cam) to drive the RPM gauge, so if they are flakey, the RPM could go wacko. Given the cost of the crank sensor (about $25) vs the ECM ($75-$150), I would try the crank sensor first.

06-21-2004, 10:43 PM
Status update: Got another ECM Sunday afternoon. Disconnected battery ground while making the swap. Started the engine, and it ran for a couple minutes, then acted like it was going to die, but didn't quite. It actually stumbled a time or two rather than just flat cutting out like usual. I drove it for 30 minutes afterward without a problem after that.

Drove it to work this morning, and it "glitched" again twice before I got there. Again I noticed the RPM gauge going wild. It didn't die either time, and I got what I believe to be the next clue: the "change oil soon" light came on right after the glitch and stayed on for 30 sec. or so, then winked back out. I interpret that to mean that the ECM lost power altogether, because when the ECM is powered up by the ignition switch and the engine is started, that's the only time this light comes on. It's possible that more than just the ECM is temporarily losing power, but I would say based on this new observation, at *least* the ECM is cutting out due to a power loss or it's just reset itself due to some internal problem.

Then some really weird (well, weird*er*) stuff happened this evening. I started it up, and drove about 100 yards and noticed that all my gauges were working except the MPH gauge, which was buried at the low end as though I was parked. So I stopped the car, shut the engine off, and tried to restart it. It didn't start back up right away. After a couple more tries, it started up, and the engine rpm climbed from idle right up to about 2500-2800 on its own, for real, with no accelerator applied by me. I tried to drive it (not pleasant with the engine rpm way high like that), got another 100 yards to the first stop sign, and it died. I got it off the road, and tried to start it--cranked, but no go. I put the timing light on plug wire #1, and this time, I verified I *did* have spark. (So I think a couple dozen posts ago when I said I thought I did *not* have spark during cranking, I now believe I must not have had the timing light sensor clamped firmly enough--the spark was probably there then, too.)

At that point, I took the negative battery cable loose, then tightened it back down. I got back in the car, and it fired right up. The MPH gauge still didn't work, and the engine rpm was still way too high, though. It got me home without glitching or dying, but the engine over-revving was a major pain.

It is my belief that the ECM I got yesterday was no good either, because this car is doing things it sure didn't do before. I don't know if reman ECMs typically come with a case seal where if you break it you void your warranty, but this one didn't. I tried to take it back tonight and exchange it, but they were out of stock and I won't be able to get one until first thing in the morning.

Because of what I saw today with the "change oil soon" light, I don't think this problem can be the fault of the crank sensor. It's either a power problem or an ECM problem or both.

Since I didn't have an ECM to replace, I spent the time checking the main battery ground; pulled the rubber cover off it and inspected it--looked good. The positive had some crud built up on it, and it looked like the crud had gotten down "into" the strands of the copper wire--you couldn't make out the individual strands. So I scraped away the bulk of this material and poured a warm baking soda solution on it to eat away the crud that had gotten down inside the cable itself. It looks pretty good now.

In the morning, I will go after another ECM. The question now is: If I have spark, and I have gas, why won't it run?

Another good question is: What the heck is wrong with this "reman" ECM that it tried to kill my engine by running it *too* hard today???

Could this problem be due to a bad battery?

I know this thread is already almost as long as Clinton's book, and I apologize for that, but stick with me here...this is not an ordinary story. Hopefully we're getting close to the happy ending...sheesh!!

06-21-2004, 10:49 PM
Forgot to ask...on GM cars is there a main power relay that's engaged by the ignition switch? If there is, I'd like to find and inspect it, too.

06-22-2004, 07:28 AM
Did you keep the old ECM, so that you could plug it back in and all these new problems go away? It does look the new one is worse than the old one. One other test which is a little harder to do is to make up a little 12v light (or voltmeter) and take off a fuel injector connector and put the light across the connector terminals. Crank the engine and the light should flash. This checks the ECM and crank sensor. If you have fuel pressure, and spark, the engine should start.

06-22-2004, 08:36 AM
No, didn't keep the old ECM - probably should have - I would have had to give the parts people another $100 for the reman if I'd kept the original. I guess I could have paid them the $200 and then took the core back for my $100 refund afterward, but I didn't.

I got the new ECM this morning. It's in, and the car starts and idles properly. With that and the newly-cleaned (+) post, let's see if it will get me to work.

(One thing I noticed about today's ECM vs. the other reman I got's has a "100% tested and certified" sticker on it, and the Sunday one didn't. I know that stickers don't make cars run, but it shows a difference in how these ECMs are reprocessed, if nothing else.)

06-22-2004, 06:23 PM
Hi All!
I am very impressed by your posti

06-22-2004, 06:52 PM
Hi Guys!
I'm sorry for that short posting of mine.
Anyway I was saying that I was very impressed by all of your knowledge. I learn a lot about the Buick lesabre. Actually I own a 92 lesabre and I am experiencing the same exact things that are discussed here. Yesterday, I went under the dash to locate the pcm/ecm and I'm not sure witch one it is it seems to me that there are two silver boxes at that location; one witch is visible and the other one hiding in the far right behind a bunch of wires.
Can someone help me locate that part?
I am tired of expending money I don't have. Last, is it easy or difficult to replace that part or should I give it to an expert.

Thanks for your help.

06-22-2004, 07:51 PM
Status update: Yes, the 2nd new ECM / PCM made the high-idle and dead mph gauge problems go away. No, it didn't get me to work without trouble; died twice going in, and glitched once coming home.

So now I'm at least back to where I was two days ago. Never thought I'd consider that to be progress, but there it is.

I have the PCM schematics now, so perhaps that will help me find all the grounds and power connections. I still think that must be it--that power is being denied to the PCM and maybe some other stuff, too.

oldysabre: If the '92 is like my '95, '89, and '90, the PCM will be the box closest to the firewall; it will have the most wires going to it. My advice to you is "don't be too sure it's the PCM." You can see what I've replaced and gone through, and mine's still not fixed. You can give it to an expert, but it may turn out that the expert winds up being *you*. I'm in the painful and somewhat expensive process of becoming one right now.

06-22-2004, 08:42 PM
In all of your exploratory maintanence here, have you ever located the PCM ground or power wires??? I am still putting all of my money on the PCM ground, you NEED to find it and clean it before you do any other work, otherwise you are taking shots in the dark. Remember that the ground that feeds the PCM also is the ground for all of your sensors or computer controlled equipment, if this connection is poor it will result in the symptoms you keep describing. I know you found that one ground post on the fender, but this really isn't the PCM ground. It is such a simple procedure to find the power and ground lines and clean up the connectors as opposed to replacing half a dozen computer components and sensors. You've spent almost a thousand bucks replacing random parts.

06-22-2004, 11:00 PM
That's what I just came in from doing when I saw your post, pcmos. I was able to get the schematics today and see where the grounds for my car were located, and it pointed me behind that squash-shaped thin metal plate under the alternator and near the ICM/coils, just as you'd said before, so I dug in. Pulled the alternator and enough fasteners until I found that "G100" you'd mentioned back in post #32. There were four small wires (two tan, two black) tied there. Then I also took the main battery ground loose on the other bolt near that. All these ground posts and terminals looked good, but I shined them all up regardless. I also polished up the alternator (+) connection.

Then to top it off (and I know this breaks my "just change one thing at a time" rule), I swapped the battery out with the one from my '90.

Got it all put back together, and it fired up. No time to test it tonight, so I'll put it on the road in the morning and report.

So far, I'm into it for a bit less than $600:

$40 - cam sensor (first thing I did two months ago, based on the lying P0341 code)
I got the 2nd new one for free [see earlier post]
$300 - ICM (replaced by my shop; swore it was bad. If so, the new one's no better)
$3 - vacuum hose (needed this anyway)
$50 - fuel pressure gauge, hoses, fittings (nice to have for future work)
$10 - fuel filter (needed this anyway)
$10 - fuel pump relay (not installed; bought when I thought this was a fuel problem)
$120 - ECM / PCM (got 2nd reman free since 1st reman was screwy)
$50 - two tanks of gas spent test driving / idling

I want to say "thanks" to everyone who's been offering help and advice on this. I sure appreciate your sticking with it.

06-23-2004, 12:08 AM
That's great that you were able to find the g100 post, I wish I had gotten you before you went out, but I was going to mention that you should probably also replace those connectors instead of just cleaning them up. I was thinking about when I did this job and I remember finding that the connectors looked decent, but that the copper wire crimped inside was pretty well coroded. I went down to pep boys and bought a package of the large diameter ring connectors and just crimped new ones onto the wires after cutting back enough insulation to find clean metal wire. It will be interesting to see how this turns out for you, I'm just hoping that those crimps on the connectors are in decent condition. I think what happens is that water and moisture kinda gets pulled up into the strands of copper wire, because I remember cutting that insulation back about an inch and still finding corroded green wire. The nice thing about working on the wiring, although it is time consuming, its ridiculously cheap. I went to walmart and found enough of the various connectors to make my own new battery cables for this car. Now that you know where the important connections are located, you can dive into it some more if things are still not working out.

06-23-2004, 06:09 PM
Well, all the terminal cleaning and the different battery made no difference. Glitched once this morning. Glitched once tonight, plus on a second occasion it died. Started right back up again--it had to crank a couple times before it fired.

I'm getting pretty depressed about the whole thing. [...rrgh...must resist urge to drive car off cliff...]

Now this corrosion issue--that describes my positive battery cable. I tried to clean it up the best I could, but there's still some blue-green junk down in the stranding, and probably far enough up into the cable that you can't see it. I think I will replace that next.

06-23-2004, 06:13 PM
Hi Tim
I have been following your posts with great interest and must say I admire your perseverence, Could you be a little more specific about this squash plate under the alternator, do you mean the plate the coils are bolted to ?

#2 where is the cam sensor located ?
I guess I am going to have to break down and buy a manual on the buick 3.8 engine so I might locate all these sensors, but all too often the books show everything but what you want to see and in this case a picture is definitely worth a thousand words, I bought one last week on the GM tranny only to find it does'nt cover 4T60-E that is in my car !!?.
Thanks for all your effort.

06-24-2004, 07:31 AM
In one of my episodes of "shotgun troubleshooting" I replaced the crank sensor. The new one caused a noticable "miss" occasionally. I put the original back in.
The crank sensor is obviously missing from your replacement list.

06-24-2004, 09:02 PM
Today's status update: Last night I cut the big ring terminal and two inches off the (+) cable that runs from the battery to the firewall. (I left the power wire to the starter alone.) I replaced it with a brand new terminal; the style that compresses the stripped cable end between two metal brackets as you tighten the bolts. I carefully inspected the old ring terminal and the stub of wire that I'd removed with it. It was pretty nasty inside. The copper wasn't shiny, and it did have some corrosion down that far in the stranding. It seemed sort of brittle, really. This wire looked just like some I had to cut out of the dash of my '91 Park Ave once when the A/C blower fan would stop running after a few minutes (sound familiar?). I cut the bad part out, spliced the good ends together, and the fan ran fine. Somebody else had done that once before I did too, so maybe GM had a design problem there...don't know.

Back to the '95 any rate, I had *no* glitches and no engine kill events today, either to or from work. Again, I know better than to get my hopes up--they've been dashed more than once on this deal. I'm thinking of getting a sign to put on my car door that says "Number of days without engine dying" and some magnetic numbers to put next to it. If I had that, today it would say "1."

creslevi: If you've read all 50-some posts in this thread without going bonkers, then I admire *your* perserverance!! The "squash-shaped" plate is just a very thin metal plate that basically keeps a couple wiring conduits back against the engine so they don't wander out into the rotating parts. If you face the flywheel side of the engine and draw a line straight down from the alternator and a line straight left from the coil pack / ICM mounting bracket, you can't miss it. My '95 has it, and my '90 and '91 have it; I can't really vouch for other years. The cam sensor is to the 9 or 10 o'clock position from the flywheel. It's easiest to find the wires and follow them back to where the sensor's tucked. It's a bit out of sight, but it's remarkably easy to work on; just held by a single bolt, and you can see the head if you lean over to your far left while looking into the engine compartment from the passenger side.

rustbucket: Yes, I have been holding off on the crank sensor replacement to this point, because I simply don't believe that's it. I probably *would* have replaced it earlier this week if not for the fact that the junk re-man ECM I got Sunday hadn't given me what I believe is an important clue. That clue is that the ECM (and maybe other systems too) is losing power temporarily. I say that because the Change Oil light appeared on the dash for 30 sec. or a minute like it does when you first start the car and the PCM has decided you need an oil change. That light was not coming on with my original ECM / PCM (which I now am convinced was not bad in the first place) because I had changed the oil recently and reset the counter. So I feel like the $120 I threw at the ECM--out of frustration, mostly--bought me this important clue. I think if you read back through the history, (I'm not recommending it, really) you'll see that the crank sensor has been on and off the suspect list at various times. I could be wrong, that the crappy re-man ECM was *so* screwed up that it was resetting itself or had an internal power failure, but right now, I'm really focused on making sure the ECM / PCM is getting good solid power and ground. And again, that's entirely because of what I read into that "Change Oil" light showing up and staying on after the glitch events Monday. The crank sensor is next on my list--if I have to go there, I will.

michelq: I agree with your opinion of re-man electrical parts. I have a fuel pump story I should tell sometime...after 3 aftermarkets, I coughed up the dough for a Delco, and no more problem. I will never do another re-man fuel pump. I was so mad, I complained to the parts house, and I called their rep that distributed the junk fuel pumps to that store and told him what I thought. He blew it all off, saying it must have been "crud in my tank." Yeah, right, jerk--that crud is called "gasoline." I might have bought his story if it'd been just one, but after three, no. Also, if it was "crud," then the Delco is somehow immune to it, proving his product inferior. If anyone wants details on that, send me a private message, and I will tell all so *you* don't get burned. I promised the guy I would tell anyone and everyone. The crappy ECM they sold me Sunday backs up your point. But I do have this second re-man in there, and I think it's OK. It's no worse than my original, at least. These re-man electrical parts look like an excellent way to keep maquiladoras in business. A buddy of mine had a PCM problem with his Camaro, and while he was researching that, he found out that some places get their units from junkyards and sell them without testing first. That may well be what happened to me! Perhaps I pulled the trigger "too soon" on the PCM change. I knew there was some risk I'd be wrong, but I thought that if I spent several hours hunting and cleaning wires (which I now *have* done anyway) and that was unsuccessful, well, the $120 expense seemed like a fair risk at the time. [Read: I was getting desperate!!]

Hey, I appreciate all of your comments. One thing about it, at least I don't feel alone. I can't wait to get to the answer so we can see which of you had this one pegged!!

06-26-2004, 12:32 AM
NO! It's still not fixed. Got me to work OK, but not home. It wouldn't start back up, and I had to leave it along the road and come back for it later. I did manage to get it home eventually, but it died twice more and restarted both times before I could get it here.

I confirmed again that there was no spark while cranking. I also confirmed that I have good battery voltage on the ignition feed signal going to pin "P" of the ICM.

My plan now is to take the car back to the shop, explain what I've done to it since they last had it, and give them another shot at finding it. At least this time it should act up for them, now that it seems to be getting worse. Last time around, that was the main problem--it never acted up in front of them.

I'm not so sure the problem isn't in the ICM that was replaced here a few weeks ago. If the shop was right and my original ICM *was* bad, then this one could very well be bad too, since the car acts exactly the same way. That would make me wonder if I don't have something wrong with the car that kills ICMs over a period of weeks.

06-26-2004, 04:29 PM
I am still having problems. I have replaced the crank sensor (agin), the ICM (agin), and plugs and wires. I am about to run this car off ofa cliff. if you findany thing else please post the fix.

07-07-2004, 08:42 PM
Having same problem here.. I was suspecting Ethanol screwing up the temps and such during warmup.. Did you replace the ECM yet?


07-07-2004, 11:06 PM
Well, I believe it is *finally* fixed. And not just because practically the whole ignition system has been changed out. I've been running a week now with no further problems.

Those of you who have said "crank sensor" turned out to be right. Even though the "pour cold water on it" test didn't work for me, the crank sensor was the culprit. I have scope printouts of the "32x" output of the sensor not transitioning between 8 volts and ground like it should. The slower, lower frequency output of the sensor remained stable throughout, but that higher frequency output was just flatlining at 8 volts. (pcmos and some of the other high-tech posters on the Forum can probably elaborate on this.) With the problem having grown so much worse since the last time I had it in, my shop mechanics didn't have any trouble making it happen and catching it in the act. They were as glad to get it figured out as I was.

So let's summarize what's been learned:

a) What should have been (and could have been—see item "c") a $50, three-hour repair in my own garage took about $800 and over 10 weeks to resolve.

b) Beware re-man ECMs from your local parts stores. You could be buying more problems than you started with. In my case, a flaky re-man ECM confused the diagnosis.

c) Never trust your ECM's codes to point you in the right diagnostic direction. In this case, not only did the ECM fail to set a *crank* sensor code, it gave a code that pointed *away* from the problem. As far as I'm concerned, some GM engineers have some explaining to do—if you're listening out there, I can't wait to hear it. Think about it: if the ECM is not going to throw a crank sensor code when half the sensor's outputs stop changing state, then when would it EVER throw a crank sensor code? I would have been better off if there had been no codes at all.

d) There's a very fine line between persistence and stupidity.

Of course there are some local people I know, who with the benefit of all this history, say "See, I told you it was the crank sensor." And that's a fair statement IF it was made back in the beginning. With just the initial evidence (a P0341 code) to go on, I don't think there's ten people in a hundred who would have gone to the parts store and bought a crank sensor instead of a cam sensor like I did. I think rustbucket, pcv, and BReynolds might have been in that group of ten people. The ECM / PCM idea seemed like it had a lot going for it, but this time, it's innocent.

My biggest regret is having paid for an ICM that I'm basically certain now that I didn't need. I wish I had asked the shop to keep the old part, because it would be possible now to prove its operation one way or the other. I guess the good news is that other than the plugs and wires, I have essentially a brand new ignition system.

Haven't decided what I'm going to do with the old crank sensor. Frame it, set it on a train track, tape it to a brick and mail it to the manufacturer, or cut it open carefully and try to figure out just what the actual failure mode was. I'm guessing there might have been a hairline crack in a circuit trace that opened and closed with temperature, or maybe one of the electrical components in there was going bad.

Anyway, thanks to all of you who posted, kept an interest in it, and stuck this thing out to the end. I don't consider myself an expert on the 3800 ignition system by any means, but I know a lot more now than I did when I started because of your help.

Hopefully what happened to me won't happen to you, and if somebody else runs into the same problem, this experience will save them some time.

07-11-2004, 06:22 PM
Well, I believe it is *finally* fixed. And not just because practically the whole ignition system has been changed out. I've been running a week now with no further problems.

Those of you who have said "crank sensor" turned out to be right. Even though the "pour cold water on it" test didn't work for me, the crank sensor was the culprit. I have scope printouts of the "32x" output of the sensor not transitioning between 8 volts and ground like it should. The slower, lower frequency output of the sensor remained stable throughout, but that higher frequency output was just flatlining at 8 volts. (pcmos and some of the other high-tech posters on the Forum can probably elaborate on this.) With the problem having grown so much worse since the last time I had it in, my shop mechanics didn't have any trouble making it happen and catching it in the act. They were as glad to get it figured out as I was.

So let's summarize what's been learned:

a) What should have been (and could have been—see item "c") a $50, three-hour repair in my own garage took about $800 and over 10 weeks to resolve.

b) Beware re-man ECMs from your local parts stores. You could be buying more problems than you started with. In my case, a flaky re-man ECM confused the diagnosis.

c) Never trust your ECM's codes to point you in the right diagnostic direction. In this case, not only did the ECM fail to set a *crank* sensor code, it gave a code that pointed *away* from the problem. As far as I'm concerned, some GM engineers have some explaining to do—if you're listening out there, I can't wait to hear it. Think about it: if the ECM is not going to throw a crank sensor code when half the sensor's outputs stop changing state, then when would it EVER throw a crank sensor code? I would have been better off if there had been no codes at all.

d) There's a very fine line between persistence and stupidity.

Of course there are some local people I know, who with the benefit of all this history, say "See, I told you it was the crank sensor." And that's a fair statement IF it was made back in the beginning. With just the initial evidence (a P0341 code) to go on, I don't think there's ten people in a hundred who would have gone to the parts store and bought a crank sensor instead of a cam sensor like I did. I think rustbucket, pcv, and BReynolds might have been in that group of ten people. The ECM / PCM idea seemed like it had a lot going for it, but this time, it's innocent.

My biggest regret is having paid for an ICM that I'm basically certain now that I didn't need. I wish I had asked the shop to keep the old part, because it would be possible now to prove its operation one way or the other. I guess the good news is that other than the plugs and wires, I have essentially a brand new ignition system.

Haven't decided what I'm going to do with the old crank sensor. Frame it, set it on a train track, tape it to a brick and mail it to the manufacturer, or cut it open carefully and try to figure out just what the actual failure mode was. I'm guessing there might have been a hairline crack in a circuit trace that opened and closed with temperature, or maybe one of the electrical components in there was going bad.

Anyway, thanks to all of you who posted, kept an interest in it, and stuck this thing out to the end. I don't consider myself an expert on the 3800 ignition system by any means, but I know a lot more now than I did when I started because of your help.

Hopefully what happened to me won't happen to you, and if somebody else runs into the same problem, this experience will save them some time.

Good job with the follow up and closure about the Crank Sensor. So many times the problems get figured out and we never hear what happened.
Your determination is admirable. Thanks for all the input.

07-11-2004, 11:50 PM
You're welcome, guys. Just today I was using the Park Avenue forum to research a problem with my blower motor circuitry, and I was thinking how nice it is when people put even scraps of factual detail in their posts--that's what makes the forum a useful tool.

With the ever-aging fleet of Buicks I drive, I find myself using this forum more and more, so I figure I should do my part to help everyone else.

07-15-2004, 07:05 PM
I'd like to second that ... it is very good of you to come back and post the "final" answer. I don't know how many times when I go looking for answers all I find is other people asking the same question, particularly with computer trouble.

Having waded through all these posts I believe I may just save myself some trouble and drive the car off a cliff now ... (Kidding!) I am having some similar problems to yours with my 94 Lesabre, ie running rough, occasionally stalling but starting up right away, I don't have a tach but I have noticed that the speedometer will jump (from 40 - 65 or so while the engine is bucking) and that the idiot lights will light up randomly (service engine soon, anti-lock brakes, temp, volts) sometimes staying lit and sometimes just flashing.

I was thinking that my main computer could be shot (I make my last payment in 2 weeks, sound typical?) but if it should turn out to be a $50 sensor, I'd be eternally grateful (or at least, until next Tuesday, whichever comes first).

All I can say is ... timrice, yudaman! Thanks for your verbosity ... too much information is better than not enough, it seems to me. If I replace the crank sensor and it fixes my problem, I'll be sure to post that information for future users as well.

07-15-2004, 11:16 PM
delhsn, I hope you get it right the first time (unlike me). My speedometer flaked out a little when I was having my trouble, too. For sure, let us all know how yours turns out.

Nice word, verbosity.

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