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94 Lesabre starts then stops; crank sensor?

11-02-2004, 03:16 PM
94 Buick Lesabre 3800. Starts, then stops immediately. Fuel pressure seems good. I've had conflicting theories on the function of the crank sensors. One mechanic says if the car starts it can't be the crank sensor, others say it probably is . Check engine light has been on for some time. Any ideas? Thanks.

11-02-2004, 04:06 PM
Test to see what codes are present. I think the 94 still has the ALCL connector, right? If it does, go to this website, and it will tell you how to read the codes.


Thank pirho451 for this link.

11-03-2004, 05:28 AM
The data from the crank sensor is not read until the engine is at operating temperature.

I've seen several post of people with cars that will run fine until the engine warms up to operating temp. The crankshaft sensor usually is to blame.

There was one test that was proposed. I believe letting the car come to operating temp and die. Then pouring water over the crankshaft sensor to cool it down, and attempting to restart the engine.

11-03-2004, 08:22 AM
In 87 manual, it says below 400 rpm. the spark is controlled by the crank sensor and ICM. Above 400 rpm, the ICM yeilds control of the spark to the ECM, so it can do things like retard spark.

11-03-2004, 08:53 AM
In 87 manual, it says below 400 rpm. the spark is controlled by the crank sensor and ICM. Above 400 rpm, the ICM yeilds control of the spark to the ECM, so it can do things like retard spark.

Thanks for the input. The car has a 16 pin connector, can I manually get the codes? Another thing the alternator gauge shows no charge, but a meter shows about 14 volts at the battery when it momentarily runs. I checked all grounds -seem ok.

I have always have Chrysler products - have rebuilt several and know them inside out, but have very little knowledge of GM's, this is actually my daughters car. The Haynes manual is limited. I really appreciate your help. Where are the ICM and ECM located?

11-03-2004, 09:11 AM
Below 400 RPM? So... the only time that would occur would be when you're starting the car right? I don't think I've ever seen a car idle at 400 RPM... then again, my LeSabre doesn't have a Tach.

I need a Tach. I also want one of those neat little displays that caculates instant MPG, avg MPG, range, etc, etc. Too bad I haven't been able to find an aftermarket version... you'd think someone would make one.

11-03-2004, 10:32 AM
My 87 idles at 725 RPM in park. Again I dont know a 94, but on 87, the ICM is under the coils packs the whole assembly is above the rear valve cover. The ECM is in behind the glovebox and is about 7" X 4" X 2".

11-03-2004, 02:41 PM
Thanks. Is an ECM from a 93 3.4 compatible with 94 3800. I have an olds with the 3.4 Are any other sensors compatible?

11-03-2004, 03:22 PM
I am guessing not compatible.

11-03-2004, 04:08 PM
Is any portion of the engine and powertrain diagnostics and driveabilty system from a 1993 3.4L engine compatible with a 1994 3.8L engine?

No. Absolutely not. Do not even attempt it. 1) The sensors won't fit. 2) There will be different sensors on each engine. 3) The wiring harness will not connect to any other sensors or diagnostic module, and if it does the wires will likely be in the wrong places. 4) If the sensors do fit, they will be calibrated with the wrong values and resistances. 5) The PCM/ECM/engine and powertrain diagnostic module is programmed to operate a 3.4L engine and associated transmission, not a 3.8L engine.

11-03-2004, 04:19 PM
To get the error codes from a 1994 pre-OBD-II car, equipped with an ECM, but pinned on a 16-pin connector instead of a 12-pin ALDL....

1) Ignition off.
2) Short pins 5 and 6.
3) Ignition on (don't start the car, just switch the car on).
4) Diagnostic read out should begin via flashing the Sevice Engine Soon, Check Engine, or similar light.
5) First code flashed will be 12. 12 is simply the "handshake" code to basically confirm the code readout is functioning properly.
6) All codes will be repeated 3 times, including code 12.
7) When code read out finishes, turn off ignition and remove jumper wire. To clear diagnostic codes, remove power from the ECM for at least 30 seconds. I.e. Disconnect the negative battery cable or remove the ECM fuse.

If you do not have a pin 6, your car does not conform to the non-standard GM pin out. The diagnostic codes are likely not manually retrievable. Send me a picture or list of the pins you have, and I'll reference the materials I have compiled on GMs use of the 16-pin OBD-II type connector in non-OBD-II cars with non-OBD-II pin outs.

View my recent post about this phenonmenon here.


11-03-2004, 10:25 PM
In general, but NOT always, GM mid-sized and full-sized sedans with the v6 have the exact same O2 sensor. Some have the same coolant temp sensor, and also the MAT sensor. If these sensors, all of which are on my '86 (3.8), are the same as the ones on a '94 Grand Am (3400), I am pretty sure that I can safely make that statement.

Interesting fact. The MAS from an '87 3.8 is not compatable with the one on the '86. The '87 has about 140 hp and gets 31mpg (non-asparated) and the '86 has about 150 hp and gets 30mpg (also non-aspirated).

11-04-2004, 12:12 PM
Thanks everyone. I ckecked the sights you referred to AVARTAR301, should be very helpful. I'll check the connector tonoght and get back

11-04-2004, 12:15 PM
Right, but how do you know if they are compatible? You have to check the part numbers on ever sensor. The O2 sensors might be compatible, they are both likely non-heated. The crankshaft and cam shaft sensors most likely are not, as they are from two different sized engines. The MAS, MAP, MAF sensors most likely will not even fit, because the engines likely use two completely different intake styles. The EGR might fit, but it's best not to mess with the EGR systems.

1994 is the year a lot of changes started happening as far as engine sensors and diagnostics. It's more likely that the sensors from a 1995, or 1996, engine would be more compatible. Then again, there are a lot of things about 1994-1996 Buicks/Olds that are completely different from other Buicks/Olds. Even within the same model year there are huge variations.

My 1995 is more compatible with 1996 parts than it is with 1995 parts. There was a huge shift mid-year 1995, and a lot of the new design for the 1996 was implimented on the 1995 to test it, as it had to be incorperated by 1996.

This is mostly due to the requirement that all cars be certified OBD-II complient by 1996. OBD-II goes beyond a standardized plug and pin out for diagnostics. It involves a huge amount of sensors and engine/powertrain diagnostics. All relating to emissions control, monitoring, and making efficent repairs of cars possible to emissions problems caused by cars needing hard to diagnose repairs.

We all think of a PVC valve as that thing that screws up the idle. In fact, it's one of the first emissions control measures. Now, it's another thing that has to be monitored. Starting in 2004, all cars must use the CAN protocol for diagnostic communication... that means no more of this 4 different adapters depending on which car you have.

Anyway, the general rule is, never mess with anything that has wires coming out of it unless you know eactly what you're doing (and have a multimeter).

Some parts will migrate between years, many parts will migrate between models of the same years, but it's very touch and go. Most sensors are related to emissions, there was a huge federally manidated emissions control systems change in 1996, manufacturers started changing in 1994. I've begun to see parts compatibility falling into these groups: 86 to 93, 94 to early-95, late-95 to early-96, 96 to 2000, 2000 to 2003, 2004.

I think one thing we can agree on is the answer to the question that was actually asked. "Thanks. Is an ECM from a 93 3.4[L] compatible with 94 3800 [3.8L]?"

Even if they use the same model and part number ECM/PCM/computer, they would be programed for two very different engines. At the very least, they use two different fuel loads, thus MOST of the sensor varibles will be different.

11-06-2004, 12:18 PM
Here's an update. The car is OBD1. 16 pin connector, pins 4,5,8,9,14,16 used. I tried the cooling down with water trick. Seemed to work first time, but second time nothing. Let it sit overnight. Started this morning and ran quite a while 10-15 min. Did not stall. Finally turned it off. Something else is happening. The gauges are going crazy. The tack goes from 0-about 5000, temp shows red , ammeter shows 0, red light is on. Fuel gauge seems ok. I tried all fuses- ok. The under dash fuses are not labelled. The two banks under the hood benieth windshield ok. Are there any others? From what has been posted I'm thinking crank sensor, but the problem with the gauges worries me. How long to change CS? Thanks.

11-06-2004, 12:39 PM
There is another set of fuses and relays behind the passenger glove box. Things like the driver door, fuel pump, and trunk release relays and fuses are back there. The fuses under the drivers dash should be labeled on the inside of the fuse box cover.

You're car actually has the same pin out as my car, it's not OBD-I or OBD-II standard, it's something else that I have yet to get completely figured out. I believe it's probably OBD-II and the wires are just in the wrong place.

FYI, on GMs with the 16-pin connector.....

OBD-II - pins 2,4,5,8,16
OBD-I - pins 4,5,6,8,16. Short 5&6 to get error codes

Our connectors do not match either of those, yours is the second 1994 LeSabre with a connector like mine. It seems the LeSabre and the Regal are the cars GM started experimenting with and sticking things in the wrong order for no known reason.

I can tell you that you will not be able to get OBD-I style error code readouts via the Service Engine Soon light blinking. I've tried shorting every combination of pins in a futile effort to find the right ones. Doesn't work.

I was actually pretty sure the car was OBD-II at that time too, but I it was an exercise in futility one night I found necessary. My best answer is that pins 9 and 14 are in the wrong place. At least one of those should be in pin 2, as that is the pin GM is standardized to use for OBD-II communications.

Now if GM actually started out using a different OBD-II communications protocol, pins 9 and 14 may also need moved to 2 and 10 or 7 and 15. They might even belong in 6 and 14, but it's highly unlikely. Mine you, I have no idea what order they connect in, those are just the pairs.

On day I'll get a wiring diagram, a 3 protocol code reader, and a week of free time, then I'll have it all figured out for good. One day, one day.

Anyway, to change the crank sensor. Well... you'll most likely have to pull the harmonic balancer off to get to the sensor. Which means you'll need a puller. You may also have to take the front axis engine mount and bracket off. Don't know, depends on the year and engine. Grab a Haynes or Chilton manual for $10 when you buy the sensor, that will be more help than someone here explaining it. LOL

Also, the lights and gages will flash and act stupid when the engine dies. As the electrical begins to drop below 8 volts everything will flash and bounce because it can't get enough power. I experienced the same thing when I had a bad battery, the tech was running an alternator test, and my engine died in the process.

11-08-2004, 09:19 AM
Thanks again. The sticker beside the rad says OBD1 compliant. Saturday I went over all connectors, removed the coil pak, checked for frayed or loose connectors, etc. Car started up, ran good at low rpm, but bad miss at mid range. The gauges went crazy, but alternator showed around 14 volts when measured with a meter, so seems to be charging ok. Car did not stall. Whlle I was sitting in it, contemplating various methods of destruction, hair pulling, the gauges all started working, the service engine light went off and it ran normally. I took advantage of the situation to drive it about 10 miles to a shop where I could work. Ran perfectly. When I shut it off and restarted same problems returned. I have a Haynes book, but from my experience with Chrysler products found it doesn't always tell the whole story. Nothing beats hearing from someone who's done it first hand. I'll go at it again.

11-08-2004, 11:46 AM
Yeah, so doesn't my sticker. But it doesn't give out OBD-I style error codes or blink the SES light. All OBD-I compliant means is "We can't say it's 100% OBD-II compliant for one reason or another."

Sierra has a 95 Regal (I believe) with a 12-pin ALDL OBD-I connector that only gives OBD-II error codes via a scan tool... that alone it just hilarious. I bet you his ELVI tag states OBD-I on it.

Read the section of the Haynes book related to Driveablity and Emissions Control Systems. That's where the crankshaft, camshaft, EGR, EVAP, MAP, MAF, O2, HO2S, and all the other sensors are discussed. Most likely your problem lies with one of those sensors. Just about every one of them functions differently depending on the temperature of the car, and just about all of them were still having the kinks worked out in 1994.

As far as Chrysler products and Haynes manuals. It's not that the Haynes manual doesn't tell the whole story because it is a Chrysler product. It doesn't tell the whole story because it is a Haynes manual. Haynes and Chilton manuals take the 2000 page factory service manual for 20 years of multiple vehicle models (I.e. 2000 *20= 40,000 pages) and condense it into 200 pages. That would be where all the really important information gets lost.

11-08-2004, 01:43 PM
Thanks. I'll continue plugging away at it. You're right on about the manuals. I'll post results.

11-12-2004, 10:59 AM
I was able to get an ECM from identical car at wrecker. Plugged it in and car functioned perfectly. Put old one back in & it continued to run perfectly. It's been fine for a couple of days, several on off cycles and several km. I assume there was a bad connection at ECM. Service engine light still comes on, but hopefully I can get it scanned. I'll take it to the dealer. What a place to put the fuses, under the glove box!! Thanks for the help.

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