89 burb stalls at 40-50 mph, help

[california-kiwi]

Hi there, My wife usually drives the 89, recently it started stalling at highway speed, sometimes slower around the neighborhood. It left a code 42 so I went through all the test steps in my GM manual and nothing I did seemed to fix it. When it dies, it is immediate, as you pull over you can hear the motor dieseling for 10 seconds or so until it stops. Then you can smell like a plastic burning smell for a little while, Then it starts and runs ok again. I have changed tons of parts , plugs , leads, cap, rotor, Ignition module, ECM, thermostat, temp sensor. Im ready to find a cliff for it to fall off.
I did observe one unusual thing, just after it stalled, the temp gauge went up pretty quickly from its normal spot to 210 or so. Back down again on restart. Im losing it on this one guys so if you can help please do. Thanks, pete.

[dirty dan]

Refresh my mind, is code 42 a knock sensor???
Temp rising on an engine which has just been shut down (and is still off) is normal.

[california-kiwi]

Hi Dan, The code 42 is the EST (electronic spark timing), this thing is running on a bit after it has died. I should say it just stops responding to the throttle and the truck starts slowing down. When you get off the road it is rattling and running on like an old 70's car when it deisels after being turned off. It smells like a pretty rich mixture and eventually stops after 20 or 30 seconds. Pete

[dirty dan]

First thing to do is to re-set your base timing. Disconnect the black and tan wire by your brake vacuum booster and set the ignition timing to 0. When the ECM codes 42, the ECM and EST let go of the ignition timing advance resulting in the spark going back to the base timing. When your base timing is set correctly, you will still loose a lot of power, but the truck should be driveable.
As far as the problem... you say that there is the smell of plastic burning. Have you checked the wiring from the knock sensor to the EST module? It runs by the starter and up behind the exhaust manifold through a sleeve. It is a common failure. The smell could just be the engine heating up due to fighting it's ignition timing.
You should be able to test your knock sensor with a timing light to see if the ignition timing is retarding when you lightly tap on the exhaust manifold above the starter. I'm not sure if there is a way to check the EST module to see if it's working correctly.

[california-kiwi]

Thanks Dan, The base timing is on zero with the connector disconnected so at least its starting out in the right place. ill take a look and see if that wire is ok and test the knock sensor. Theres another small sensor on the left near #1 plug, do you know what that one is? Maybe there are two knock sensors on these 89's. Pete.

[dirty dan]

The single wire sensor between the 1 & 2 plugs is for your temp gauge. The temp sensor on top of your intake (by the thermostat) is just for the ECM.

[Redonthehead]

I had an '89 burb that the wife drove. She said it was real doggy at 40+ mph. I blew her off for a couple of weeks until she really whined about. I drove it and jeez, it had no power. Mash the pedal and it would puke. Turned out it was the fuel filter. Maybe not your problem but if it hasn't been changed in 50K I would certainly do it.

[california-kiwi]

Originally Posted by Redonthehead

I had an '89 burb that the wife drove. She said it was real doggy at 40+ mph. I blew her off for a couple of weeks until she really whined about. I drove it and jeez, it had no power. Mash the pedal and it would puke. Turned out it was the fuel filter. Maybe not your problem but if it hasn't been changed in 50K I would certainly do it.

Thanks, I hadnt even thought about the fuel filter. It has been a darn long time since that was changed. regards, pete.

OK Guys, I got the darn thing. The stalling after running for a few minutes was being caused by the distributor pickup coil. I live near the ocean and the coil had been corroding for a long time. As it warmed up a bit, the coil insulation was breaking down and causing the spark to stop intermittently. Then it would half run at really low revs (bringing up the code 42) and die. It has run great for a whole week now. Quite a relief. Im putting this here in case anyone else is having a similar problem. Thanks for all the input, its always helpful to hear other viewpoints. Pete.