1996 Lumina problem

[snappin]

We've got a 1996 lumina 3.1 that has been great until this year. We had the intake manifold gasket replaced, and soon after that we started having real problems. We would be driving along and then the car would go dead - no symptoms otherwise. We could wait a while, then it would start up and run fine for another two or three weeks. Took it to a shop and they changed out a bunch of things trying to find the problem: camshaft sensor, PCM, two reman injectors, new injector wiring harness, egr, crank position sensor. I've had the ICM checked and it's fine, and the coil packs are fine as well. For the last couple of weeks if the car was cool then it would crank right up and run very smooth and then after heating up it would die. It's now to the point where if the car has been cooled off you can crank it and it'll run rough for about a minute, then after it heats up the fuel pump stops getting power.
Fuel pump has just been replace, relay works fine. Something seems to be heating up and telling the computer to stop sending signal to at least the fuel pump if not the injectors as well. I was hoping it was the oil pressure switch not working right, but we've also bypassed it by sending a constant signal to the fuel pump and the engine still dies. Any ideas would be helpful.

[CNCguy]

I would be suspect of the CPS (crank position sensor) in the rear of the block or the ICM but there could be another cause. The engine has two crank sensors, do you know which crank position sensor they changed? A bad cam sensor or the crank sensor behind the dampener should not make it die. Has the fuel filter been changed? To eliminate the fuel supply issue, you can connect a fuel pressure gauge and watch to see if the pressure is dropping off and killing the engine. They have loaner gauges at Autozone if you don't have one.

[snappin]

I would be suspect of the CPS (crank position sensor) in the rear of the block or the ICM but there could be another cause. The engine has two crank sensors, do you know which crank position sensor they changed? A bad cam sensor or the crank sensor behind the dampener should not make it die. Has the fuel filter been changed? To eliminate the fuel supply issue, you can connect a fuel pressure gauge and watch to see if the pressure is dropping off and killing the engine. They have loaner gauges at Autozone if you don't have one.

When I get home I'll try to find out which crank sensor they replaced. I did changed the fuel filter and it's getting plenty of fuel when the pump is actually getting a signal. When it does run it's running really rich. You can really smell the gas in the exhaust. I have checked the fuel pressure and it's getting good pressure.

[snappin]

On the receipt it just says "Crank Sensor." The cost was $42.08 if that makes a difference. Also there was a shift sensor that was replaced as well.

[Tbay99Venture]

I don't know if '96 is MFI or SFI, but there was this post from some time ago that may be helpful:

http://60degreev6.com/forum/showthre...l=1#post359099

Though it will be hard to identify the offending injector. (How did the shop settle on the 2 they replaced?) You could try putting an empty can into a pot of water on the stove, bring the water to a low boil and warm the injector within the can. After about 5 or 10 minutes you could check it with (gloved hand) an ohmmeter for shorts or opens. Confirm all injectors are OK with heat.

[bszopi]

96 would be SFI. But remember, the fuel injectors only fire sequentially at lower RPMs. Whenever going WOT, the system converts back to batch fire.

[snappin]

I was told by the shop that they ran the car until it went dead and then they hurried and tested the injectors to see which ones were not at the correct ohms. I've never tested injectors before, but this sounds like a pretty simple test for the most part.
Also I noticed that they didn't put any dielectric compound on the ICM, is that something that I should do or is that something trivial?

[talon2swords]

Deleted.

[snappin]

I'm taking this week off working on it, I'll resume next week by taking out the injectors and testing them one by one

[CNCguy]

I wouldn't waste time pulling injectors at this point. You need to do some diagnostics first to narrow down where the problem lies. Does it have fuel pressure when it won't start? Do the coils fire? Will it start if you spray starting fluid into the throttle body?

[Joseph Upson]

I'm putting my money on your PCM as the problem. You describe an issue that gradually grew worse. Crank sensors usually don't come back to life when they go bad, injectors going bad in pairs is pretty much unheard of and if they did the results would be persistently bad for the most part and they wouldn't stop the fuel pump. The fuel pump will not prime if the PCM does not tell it to so if the pump and relay are good as well as the associated sensors I would start suspecting the PCM. My ECM blew its fuse a couple of times and occasionally made the car stumble before it finally made the situation clear when it started to burn and give off smoke.

The ignition module is the other suspect given your problem's sensitivity to temperature, the more assessories you turn on, the harder and longer you drive the car and the warmer it is outside, the hotter these two pieces of electronics get. I believe your PCM is under the hood so it will definately feel the heat along with the module. It appears the mechanics threw parts at it and crossed their fingers.

Here are two ecm related issues current on the Fiero forum now:

http://www.fiero.nl/forum/Forum2/HTML/111033.html

http://www.fiero.nl/forum/Forum2/HTML/107810.html

[snappin]

I was thinking it is the PCM as well, but unless I tow the car to the dealership and have them to hook it up to their computer there is no way, that I know of, to test the PCM. If we bypass the fuel pump relay and it's getting gas it still doesn't run until it cools off for a while, then it'll crank up and sputter. I figure if it's getting gas to the injectors, getting spark, getting air, then maybe the PCM isn't telling the injectors to fire. Like I mentioned before when it does run you can really smell the gas in the exhaust. I can get a remanufactured PCM for $100 and then it's another $50 to have it flashed. But I don't want to put another $150 into it when I don't know for certain this is the problem. I've put waaaay more into the car then what I wanted to. Anyone know of a way to test the PCM? I've asked a dealership if I could just bring it in and they said "no", no surprise there.

[snappin]

Well I finally got the car back from the mechanic and he ended up putting a used PCM from a salvage yard in and it fixed the problem. I'm still in the process of driving it and making sure it's fixed, but as of right now that's what the problem seems to have been.