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.

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[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?