1990 Grand Prix 3.1 V6

It's possible that the transmission itself is shifting into neutral from drive. It could be something as simple as a linkage problem. It could be about a lot of other things.. But the problem needs to be identified as opposed to simply swapping parts, especially expensive ones.

Computers are expensive. Replace them only if they can be identified as the fault and can then figure out why it failed. Did it fail due to an electrical short? If the short still exists, it'll just kill another computer.

Go to a real mechanic (ask your state's equivalent of the Bureau of Automotive Repair to recommend somone if you don't know of anyone) and ask them to "diagnose" the problem. Expect to spend for about 2 hours worth of labor, but its cheaper than dealing with people who just blindly replace parts.

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Thanks, Barry, for the info. I guess that I wasn't clear. We have had it hooked up to a computer a few times. The mechanics have (supposedly) changed what they thought was the problem and it still didn't fix it. Of course, the Chevy dealer said that they would replace the injectors and that it would only cost $1000. That was mighty nice of them. But I just have a strong feeling that if the injectors were the problem, it would be running like crap all of the time.

They have tried changing the crank sensor, the fuel pump, and the ignition module -- all to no avail.

Hope this helps some, Chris

$1000 -- Based on what? They never ID'd the problem.

I had an early 90s Saturn throwing a "knock sensor activity high" code. The knee jerk reaction would to replace the knock sensor. After poking around with a stethoscope for about 2 hours, I found that the bearing on the alternator was intermittently knocking. The bearing was going bad. I also found that the power steering pump was also on its way out. The alternator was the ultimate culprit though. It was actually causing a knock which the knock sensor and computer picked up.

I once had a dead injector on a 4 cylinder Nissan. The thing vibrated like hell. It was also quite obvious when I looked at the spark plugs that one hadn't been firing. I then checked the 4 injectors with an ohmmeter. 3 were at 12 ohms. (within spec) 1 was at 1 ohm. One injector was shorted out. 1 injector is a lot cheaper than 4 and I was able to narrow it down to just that one fuel injector. Replaced the injector and the engine stopped vibrating.

In this case, a '94 Nissan Altima. The computer said everything was fine.

Computers are no substitute for thinking on the part of mechanic.

It sounds like you need a real mechanic, not a parts changer. May I suggest contacting your local community college automotive technology problem and see if they'd be willing to diagnose your car or see if they can refer you to someone who can actually identify the car's problem. State agencies that regulate car repair may also have recommendations.

Regards, Barry

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This may be a silly question, but have you checked the ignition modules, and plug wires, a plugs? My 90 olds with a 3.1 was running like crap etc, I gave it a good ole tune up, and it runs great now.

Never hurts to improve grounds. Stainless Steel bolts repel electrolisys.

" If your going to critize my spelling, get an English Teacher to fix your car "

I used to have a 89 grand prix with a 3.1 L. I had to replace all the ignition coils on it...there should be three of them. I also and to replace 2 injectors. I haven't had too much problem with this cars just your normal repairs (brakes, alternators...things of that sort). But I have noticed that the ignition coils have been moved to a different location on newer 3.1 motors..but not sure where it is on your 90 GP. Mine were kinda under the front of the motor near the radiator.

Good Luck

This may sound weird but are you experiencing a coolant loss? I have a 3.1 with the all to famous coolant leak caused by the intake manifold gasket problem. Unfort, though I found out almost too late. My car ran fine and then gradually started to run worse, like yours. then it developed a a knock. then it is now starting to mis fire because of crap (coolant and oil) in the cylinder. this spring I am going to pull the engine apart and see if it may be salvagable. luckily it hasn't snapped my camshaft like you can read about on gm-v6lemons.com. I have had mechanics check out all sorts of stuff, no codes, no fuel problems, but we never pulled the intake off. I was told it had a leaky gasket but I didn't know about the mass problem with them so my mechanic tightend up the bolts some and it got better but some damage had already been done.

Anyway, I would look there. It can cause lots of problems that look like other or unknown things,