88 astro stalls, trouble code 42

I'm stumped guys! Please help!:screwy:

88 Astro, TBI, it consistantly stalls after about 15 minutes of running it, whether at idle for 15 min. or driving it for 15 minutes. The error code right now is #42 and #43 - the Electronic Spark Timing, and ESC. Previously it also showed code #33 - MAP sensor. In the last short while its had a new MAP sensor, Ignition module replaced twice, EGR valve replaced, alternator replaced (earlier), new plugs and wires, new dist. cap and rotor, new air filter. The local mechanic who replaced the ignition module doesn't seem to have a clue.

I read on one forum that 80% of the time this code #42 has to do with a faulty EST circuit, such as a damaged wire, or plug-ins. This still MAY be the problem, I don't know. I unplugged all the electrical connections involved with the ignition module, the ESC module, etc, and cleaned them with electrical cleaner, hoping to fix a short. STILL stalls after 15 minutes of a cold start. I also thouroughly cleaned the throttle body and injector casing with cleaner. Oh yes, and the fuel filter has been replaced twice just in case. Observing the injectors with the air cleaner assembly off, I'm fairly certain they're functioning properly.

Is it a wiring problem? A ignition module? TPS sensor? ESC module? knock sensor? ECM computer failure?

How would I use a voltmeter to test these? Or what other tests should I do? I DON"T want to start replacing everything like some others have done, to no avail.
:banghead: PLEASE HELP!

I should also mention the way it stalls out, does feel like its mis-firing, but I know its not the fuel responsible for that - cus I'm watching the TB injectors as it stalls out. I think it is a timing problem caused by the communication between the EST, ESC module, and the ECM. But what CAUSES it??? And what should I replace?

If you have or can borrow a timing light you can test the knock sensor.
Helps to have an extra set of hands-
Observe the timing marks with the timing light, then rap on the block near the knock sensor with a big wrench, you should see the timing retard slightly. If not it's likely the knock sensor is gone.
If the voltmeter happens to be a multimeter, you can further test the knock sensor. The resistance between the center terminal and the outer body of the knock sensor should be about 3900 Ohms. If it's not close to this it's toast.
As electrical circuits heat, resistance increases. Since it's running ok for 15 minutes or so, this leads me to the knock sensor since it's screwed into the block - first suspect component to heat up.

That taps my thoughts...next?
good luck

I'm stumped guys! Please help!:screwy:

88 Astro, TBI, it consistantly stalls after about 15 minutes of running it, whether at idle for 15 min. or driving it for 15 minutes. The error code right now is #42 and #43 - the Electronic Spark Timing, and ESC. Previously it also showed code #33 - MAP sensor. In the last short while its had a new MAP sensor, Ignition module replaced twice, EGR valve replaced, alternator replaced (earlier), new plugs and wires, new dist. cap and rotor, new air filter. The local mechanic who replaced the ignition module doesn't seem to have a clue.

I read on one forum that 80% of the time this code #42 has to do with a faulty EST circuit, such as a damaged wire, or plug-ins. This still MAY be the problem, I don't know. I unplugged all the electrical connections involved with the ignition module, the ESC module, etc, and cleaned them with electrical cleaner, hoping to fix a short. STILL stalls after 15 minutes of a cold start. I also thouroughly cleaned the throttle body and injector casing with cleaner. Oh yes, and the fuel filter has been replaced twice just in case. Observing the injectors with the air cleaner assembly off, I'm fairly certain they're functioning properly.

Is it a wiring problem? A ignition module? TPS sensor? ESC module? knock sensor? ECM computer failure?

How would I use a voltmeter to test these? Or what other tests should I do? I DON"T want to start replacing everything like some others have done, to no avail.
:banghead: PLEASE HELP!


Here is a good link on code 42.
http://www.troublecodes.net/articles/gmmsundrstd42.shtml

Also give the old pcm a tap or twist test when it does it.
MT

:grinyes: I'm thrilled to say, my knock sensor failed the ohmmeter test. Instead of the expected 3900 ohms, I got about 100,000 ohms. Gonna replace it in the morning when there's daylight. Hope it solves the problem...

Well, it seems to have fixed the problem. I switched the knock sensor and the ESC module, and reset the ECM by disconnecting the battery. And note that carefully - I learned the hard way, that you MUST reset the ECM trouble codes by cutting out the power to it. Even after replacing the parts, I found it was necessary to clear the trouble codes before all the symptoms went away. Figure that one out!!

Well, it seems to have fixed the problem. I switched the knock sensor and the ESC module, and reset the ECM by disconnecting the battery. And note that carefully - I learned the hard way, that you MUST reset the ECM trouble codes by cutting out the power to it. Even after replacing the parts, I found it was necessary to clear the trouble codes before all the symptoms went away. Figure that one out!!

Glad you got it fixed.
And yes you always need to clear codes after a repair.
A lot of times when a code is set the computer runs on a fixed or subsitute value.
And on a 96 up the codes need to be cleared with a scanner.
The have a memory like a elephant the old battery disconnect will not erase codes on them.
MT

well well well,

I spoke too soon. STILL haven't got this thing to stop stalling. The van runs alot better, most of the time. I drove it around to test it, a few times. Each time it ran great for the first half hour, on the highway, stop-and-go, it was fine. Then while driving along at about 50 kph (35 mph) it "hiccups" once, and so I pull into a gas station. After idling there for about 2 minutes, the idle then started to lope/surge a few times. Seconds later it stalled out. It started up fine, drove it down the block, kept it slow, pulled over to idle and it stalls again. So I tried this a few times during the day, and same thing each time. Once or twice when stalling the engine even tried to recover the idle, but died seconds later.

I get no error codes now. I guess the EST and ESC circuits are fixed. What else could be the problem???

My best guesses:
Vaccum lines? MAP sensor (already replaced I think, but who knows)? O2 sensor??? Ignition coil? Distributor coil pick-ups? ECM wires? PCV valve?? fuel filter (again???)?

PLEASE HELP ASAP!

well well well,

I spoke too soon. STILL haven't got this thing to stop stalling. The van runs alot better, most of the time. I drove it around to test it, a few times. Each time it ran great for the first half hour, on the highway, stop-and-go, it was fine. Then while driving along at about 50 kph (35 mph) it "hiccups" once, and so I pull into a gas station. After idling there for about 2 minutes, the idle then started to lope/surge a few times. Seconds later it stalled out. It started up fine, drove it down the block, kept it slow, pulled over to idle and it stalls again. So I tried this a few times during the day, and same thing each time. Once or twice when stalling the engine even tried to recover the idle, but died seconds later.

I get no error codes now. I guess the EST and ESC circuits are fixed. What else could be the problem???

My best guesses:
Vaccum lines? MAP sensor (already replaced I think, but who knows)? O2 sensor??? Ignition coil? Distributor coil pick-ups? ECM wires? PCV valve?? fuel filter (again???)?

PLEASE HELP ASAP!

Give us time here . Good help is like good wine it takes time.
A lot of people here have regular jobs to take of so be patient.
Bear with us.


You need to do some proper testing.
Recheck for codes.
When it starts acting up or quits.
Check that fuel pressure.
What is the fuel pressure reading?
Check for good hot blue spark to plugs.
Is it losing spark or fuel or both.
Give the old pcm the tap or twist test.
MT

with the engine idling, spray some starting fluid around the base of the throttle body. If you notice a change in rpm, the gasket is leaking.
Being an '88 my bet is that the gasket has turned to mush.
If you find this to be the case, I recommend rebuilding the throttle body while it's removed to install the gasket.
The pcv port in the model 220 takes a 90 degree turn just inside the TBI that collects a lot of carbon. Injector cleaner and spray carb cleaner won't remove this.

I am with MT. Check that fuel pressure. I'm betting you have a failing fuel pump, fuel pump relay or ....what's that other thing in the tank with the pump called...... a pulsator?

I don't think the '88 has a pulsator, at least my '89 doesn't. (maybe I'm missing a part...)
but along that same line of thinking, the fuel pressure regulator might have failed.

Like MT and CD I recommend getting the fuel pressure tested.
It's more likely the fuel pump is giving out. mine kicked the bucket at 86K.

Since you're already painfully familiar with the distributor, remove the doghouse (yes, again) and distributor cap and rotor. Unplug the small two-wire connector from your new (second time) ignition amplifier/switching module, and test the resistance between the two wires in the connector (the pickup coil). That should indicate between 500 and 1,500 ohms - 850 is perfect. Also test the resistance of both wires to ground - There should be infinite resistance (no continuity). Inspect the wires themselves for damaged insulation or cuts. While you're there, inspect the condition of the pickup coil, looking for signs of damage, overheating, missing insulation, etcetera. Also inspect the reluctor (the six-legged pole piece) for cracks, damage, and interference with the pickup coil. Verify that the reluctor is firmly attached to the distributor shaft and is not slipping.

Before you reassemble and close everything back up, check the radial and axial play in the distributor shaft. There should be almost no radial (side-to-side) play, and between 0.018-0.025" of axial play. I've seen them run with almost 1/8" of axial play, but that can make a reliable pickup signal difficult to generate under the right (or wrong) conditions. If the axial play is out of tolerance, you can remove the distributor, remove the lower (driven) gear, and install shim washers to correct the cleanance and position the reluctor to the pickup coil properly. Mr. Gasket, Accel, and several other aftermarket companies offer distributor shim kits just for this purpose.

Repair anything you find wrong. Install the rotor and distributor cap, and start and run the engine until it's warmed to operating temperature, or until it stalls. Once it is warmed (or has stalled) remove the distributor cap again and check the pickup coil resistance again. If it has changed more than 200 ohms (usually less) the pickup coil is suspect. You can heat the pickup coil and reluctor with a heat gun or hair dryer and continue testing. If at any time the resistance increased to 1,500 or above, the pickup coil is failing.

thank you guys for your ideas. "Blue Bowtie", I like your idea of testing the pickup coil wire resistances. Excellent thought. I'm gonna try that right now.

The van ran great for a few days, then crapped out again and again. It finally gave the trusty old code 42, again.

So as for fuel pressure... I'm fairly certain that it has nothing to do with fuel. When the car stalls out, it starts up again immediately. And what's more, when I start it up, the excess fuel from the stall is blown out the exhaust - hence indicating that there's no spark when stalling. This is clearly a timing/spark issue.

And as I read more and more about this code 42, and some other posts, I'm figuring it wise to thouroughly examine the BYPASS and EST wires running from the ignition module to the computer. Either the ignition module is failing (perhaps due to a bad pick-up coil), or the wiring harness isn't doing its job, or the wires are shorting out, or the ECM is hooped. Still a good possibility that the ECM is the culprit, but first things first I suppose. I'm gonna go to some ohm meter tests and report back...

thanks again!

Well I tried a few tests. Nothing I could find to be wrong. I checked the resistance on the pickup wires. It was about 900 when cold. I checked it again after it stalled (after 20 min. of running), and it was about 1000. Not a big change, so I suppose that works ok.

The pickup coil is kinda rusty. Don't know if that's normal. And it looks different than any picture I've seen of a pickup coil. Its got this metal "sleeve" overtop of the coil, that I can't seem to remove. I don't know if I should be able to remove it, but it blocks my view from examining the rest of the pickup coil. And the "sleeve" has a 1/4 inch of rotational play around the coil. I have no idea if this is normal.

Anyways, I'm once again at my whit's end. :banghead: :shakehead :frown:
The distributor and coil have the right amounts of lateral and vertical play.
I gave the 6 connectors pins for the ignition module a little bend so that they'd stay snug in the connection. There was also a separate single-wire connector on the EST Bypass wire (tan and black wire) that I checked and cleaned. I also pulled out the ECM and wiggled all the wires there. Heck I wiggled as much of that whole EST circuit as I could, to see if it had any noticable effect. NOTHING!

What do I do guys? After clearing the trouble code memory, when it stalls its still giving me code 42. Can the ignition module (already the 2nd one in there) be failing again? More importantly, can it fail intermitently, and esp. when the van is running hot??

How easy is it to remove my ECM and put in a new one? Is it just plug and play, or is there programming involved? I realize the ECM's are very model/make specific...

Well guys, the van is FIXED! Halejuljah!
I spent most of Sunday with a guy in my area who has a few of these Astro's in his yard. What really set me off in finding the true problem was listening to what a real Astro is supposed to sound like, in many different states. Most particurly, in diagnotic mode (when you connect ALDL terminals A + B). Since I bought it, it had made this funky sparking sound, coming somewhere from the TBI unit, but I coudn't pinpoint it. I assumed that it was a natural sound during diagnostic mode. But then I noticed that after the van stalled, and I left it with ignition still on, I could hear this muffled sparking sound. It sounded irratic and random, sometimes going for 20 seconds before it'd sound again. Guess what it was. The sparking noise was coming from the injector electrical plugs! So at first we thought, why not swap in a whole TBI unit since we got one sitting here. Van ran better, but the "sparking" sound soon reoccured after a short test drive, then it stalled. So really there wasn't any other choice - it had to be the ECM brain. And so we threw in the closest model we had sitting around. Same service number, from the same type of engine. VOILA! Holy crap we did it! Have driven it all day and night since, and its running fantastic.

I'm telling you guys, if any of your vans are giving multiple trouble codes, suspect the computer. And if you can try another used ECM in yours as a test, I'd highly recommend it. These computers, honestly are far too finicky. The trouble code 42 had nothing to do with the actual problem. I may or may not go get my computer reprogrammed. It should be worth it, for $100 or so, to have a spare working ECM around...

By the way, thank you all for your help and advice. I know you all have lives and busy ones at that. I'll be sticking around this forum... its a very helpful site.:grinyes: