1996 Camaro 3.8 V6 RPM drop/stall problem

[quote=”eHowitzer” post=76747]My son’s Camaro intermittently drops RPM (about 1500) for a split second, or stalls if at low RPM. This can happen after a few minutes of driving, or much longer. Sometimes when this problem occurs the engine will not start. It cranks but doesn’t catch. There are no codes on the OBD.

When in the failed state, I can hear the fuel pump run when I turn the key to the “on” position, and there is fuel under pressure at the fuel rail (manual check, not with a fuel pressure gauge yet).

If you let it sit for some time (30 minutes?) it seems to start just fine.

I am a novice, so what is the best way to go about diagnosing this problem? As always, any help would be appreciated.[/quote]

Next time it will not start check and see if you have spark.

Those engines were known to have coils that would get hot and stop functioning until they cooled back down. If you do not have spark dont go out and buy a coil just yet, let us know and we can help walk you through the next steps to ensure it is a coil problem.

Good find College,

Yeah those systems were plagued by issues, for a GM bypass system they sure were not reliable.

In the 3.8 series engine I have seen coils short and shut down the ICM, ICMs go bad, cranks sensors fail when hot and even the cam trigger magnet fall out of the cam gear and cause strange running issues and horrible mileage as the PCM is forced to go from sequential firing of the injectors to continuous firing.

You know Bill, this case reminds me of why I went into drive-ability and diagnostics. In the first month at my first repair shop we had a identical case come in, a 3.8 that would get hot and stall. The head tech said “That’s easy, crank sensor” we did that and the next day the car was back with the same problem. So the tech said “no problem, it’s the control module” so we replaced that and sure enough the next day it was back. So he said “well, got to be the computer” and once again the boomerang car was back the next day. So he called another tech that worked at a specialty shop to come in, the specialist hooked up a scope with remote leads and went for a drive. When it died he started running tests based on what he saw and found the 1/3 coil was shorting when hot and shutting down the ICM. After seeing that, I was so impressed I went out and bought a graphing meter (OTC Perception) a bunch of college text books on automotive computer systems and started studying.

[quote=”wysetech” post=76799]Raistian77, You are absolutely correct but without these cars and owners in front of us and have thousands of dollars worth of tools and test equipment at our disposal and hours of time to spend all we can do is give an educated guess and the best advice we can based on Eric’s videos, the internet and our own experiences. Sometimes we give the right advice and sometimes we don’t.[/quote]

I know, it is a weird new way of looking at repair for me.

In another thread I recommend replacing a part to test the old one and my wife (lurks now and then) asked me latter “You always recommend testing over replacement” and I had to tell her the cost of the parts was much less than the cost of the tool to test the part.

I guess if I was the OP and really was unsure of testing I would replace the crank sensor first, it is the most common failure Item and costs the least amount of money.

Like Ford used to say
“substitute known good part and recheck”

The main crank sensor is a known failure point.

[quote=”eHowitzer” post=76875]Update: Since I don’t have all the tools I need to troubleshoot properly, I thought I’d take a chance and replace the crank position sensor. It’s an inexpensive part, so I thought I’d roll the dice.

No joy. 🙁

Behavior is the same, although this time it happened only 5 minutes after driving.[/quote]

Try this
http://easyautodiagnostics.com/gm_ignition_3800/test_ignition_module_1.php

The only tools needed are

1. A Multimeter.Either a Digital Multimeter or an Analog Multimeter can be used

2.An LED light.
You can buy this bad boy at any auto parts store (like Auto Zone, O’reilly, Pepboys) or do like a do.. I buy mine at Radio Shack (they’re cheaper there).

3. 12 Volt Test Light.
When testing for power (12 Volts), you can use the test light instead of a Multimeter.

In a no-start condition is the accelerator pedal left untouched or will the engine not start even if the pedal is depressed a bit?

If the pedal is left untouched it could be that this problem is related to the Idle Air Control valve. If the pedal is depressed and the engine will not start anyway then it’s not likely an IAC valve problem.

I’m in full agreement about testing but sometimes problems exist for which no amount of testing will diagnose.
Shotgunning something on a wing and a prayer is distasteful but sometimes there no alternative and many car manufacturers resort to the replace and hope methods.

An example could be a Toyota service bulletin about coil failure in which they recommend moving the coil around to see if the miss follows it or Volkswagen stating that if all tests show good then to try replacing……. 🙁