Electrical woes - possible PCM issue

[hammerheart]

I've been out of town for over four months due to a family emergency.

I just got back this weekend and the 1992 SSEI's battery is dead. After a few hours on the charger I tried starting the car - sure enough it fired up, BUT I saw smoke coming from under the hood from in front and behind the engine and it smelled like rubber/plastic/electrical stuff burning. I shut off the car and the smoke stopped.

I've already had to replace some wiring pigtails on this car (crank sensor and some other) and I'm no big fan of automotive electrical work. Would it be easiest/best for me to pull out the entire engine wiring harness (labeling as I go) and look for breaks or signs of damage?

Can an entire harness be purchased at once?

[CatmanFS]

I wouldn't pull the entire harness, getting all of that back into place is a pain.

Just make a list of the electrical connections and go down it, checking each one as you go. Find the problem area before you take anything apart.

[Tim's Buick]

Are you quite sure something didn't sieze up in your accessory belt area? I've seen alternators do this, burning up the belt causing what you describe.

[hammerheart]

I'll check the belt, and I'd thank my lucky stars if that ends up being the problem.

[RJolly87]

Was it right as the car started, or as it was warming up? Did the smoke stop right when the engine stopped, or a bit after? Any noises, or indications that something wasn't happy?

I ask, because the valve cover gaskets are known for leaking. When they leak, they leak down the engine block, and on the exhaust manifolds as well. Any other leaks that leak on to the manifolds, or any other parts of the engine that get really hot, will burn off as the engine/manifolds warm up, smoking in the process. Burning oil smells similar to burning rubber, especially if there is dirt/dust mixed in there too.

I would determine where it is smoking from. If there is no specific part that you can locate that is immediately causing it, and there is no impending destruction that you can tell, I would just let it run, and monitor it as it warms up. It will likely smoke for a few minutes, and then stop once everything is burned off.

[hammerheart]

I think the engine ran for about three minutes before I noticed anything. The smoke stopped very soon after shutting off the engine.

[spoiledred94]

I don't think letting it run for awhile longer is a great idea. Chance of a bigger and more dangerous fire is a potential. Other wise it would be easier to locate. So look around and follow the harness' and inspect all the valve cover gaskets

[hammerheart]

Well the smoking problem has been cleared up. I checked around and sure enough the smoke was coming from the exhaust manifold. Mystery solved.

There are other problems though. I took the car out to get it inspected and it stalled while cruising about four times. I'm in the process of getting a diagnostic scanner to check to trouble codes.

What's the likelihood that the car has trash trapped in the gas line due to it sitting for over four months that could be causing it to starve and stall?

[CatmanFS]

You might want to check the throttle body for excess buildup. Anything dirty, grimy looking around the mouth of the intake can mean there's a lot more further inside. I had an issue where the car would seem like it wanted to die, i took it to a shop and they did something like an intake purge and sprayed a bunch of throttle cleaner into the intake and vacuumed it out. Car ran great ever since.

[RJolly87]

It also could be bad gas or water in the gas

[hammerheart]

Well I ran it out of gas (on accident) and then filled it up. Still stalling.

Oy. I'll need to be thinking about this one while I'm under the dash replacing the headlight high beam switch.

When it rains it pours.

[hammerheart]

Dash off and back on again and huzzah, I have headlights again.

I looked under the hood and found evidence that a cat had been camping out under there along with a disconnected vacuum line. That may be the culprit as far as the stalling goes.

It's been a good day.

[hammerheart]

Well it wasn't that good of a day. The vacuum line was likely just blown off when the engine stalled at 60 mph. The thing left me stranded yesterday. Stalled and wouldn't fire back up.

I'm going to test the coil packs first, then I'll need to go rent/buy a fuel pressure gauge.

[hammerheart]

Well the coil packs check out okay and the fuel filter didn't seemed clogged.

I'm pulling the plugs and checking them all now. I'll check the throttle body/MAF afterward.

No testing in-between items because the battery is dead and charging atm.

[Bing]

Try starting it with the MAF unplugged. It should start and run even with the MAF unplugged if this is the culprit.

[hammerheart]

Roger.

While pulling plugs I found the O2 sensor wire has been chewed on and only has two internal copper threads still connected. I'm not sure that this would result in the car stalling/failing to start, but it's not good. Since (I think) it's a resistance based sensor, a weakened connection would raise resistance and provide junk info to the PCM.

[hammerheart]

I started the car and let it idle up to standard operating temperature. Unplugging the MAF sensor made no difference, sadly. It still died shortly after it got to operating temperature and wouldn't start back up.

I'm going to start pulling some wiring harness today and looking for breaks/melted stuff.

[hammerheart]

Alright just pulled codes using the paperclip trick. I got the following:

17 - Spark Reference Circuit and
34 - Mass Air Flow Sensor Circuit ( Grams Per Second Low )

I'm think that the MAF one is simply because I had disconnected the sensor.

Thoughts? Ideas? Recrimination?

[MattStrike]

ICM, its wiring, or PCM. Terminal GD6 on the PCM should have ~3v on it when at idle after 1 minute. That is 5v with key on engine off. If not, check wiring, ICM. If voltage is good, it's a PCM problem.

But this DTC won't set a SES light alone. And only impact the engine when operating below 1200rpm.

[hammerheart]

Whoever "organized" the FSM should be beaten with shoes.


Voltage checks out okay.

The ICM connector is in rough shape - lots of bare wires, but not the Spark Reference wire.

I'm idling it up to operating temp to see if it shuts off again or if some of the wires I replaced fixed it.