Thread: driveability, engine cutting out - help diagnose

My son got the 2001 GTP hand-me-down. We just finished some maintenance with a new crank sensor, (CKP) harmonic balancer, water pump, supercharger isolator and belts. We did this maintenance because it died and wouldn't immediately restart. When it did restart, it would run smoothly, then the engine speed would occasionally drop and nearly die. Got it towed home and changed parts.

It no longer dies. However, both before and after changing the crank sensor the engine will occasionally cut out under acceleration, for no more than 1/2 second. Other than that it runs fine. The check engine light hasn't come out, I have not yet scanned it for stored error codes though. One thought that occurs to me is the throttle position sensor (TPS) may have a dead spot. I'll check this with an ohmmeter in addition to the code scan this evening.

Anything else I should check for? Do these symptoms describe a well-known common problem for this car?

Start the car and tap with your finger nail on the maf sensor. Anything happen?

Also check that the connector going to the ICM is on. The 7mm bolt should be just snug. No need to crank it, just snug. Those would be the couple of things I'd check first if nothing is obvious and from your post, nothing is.

I tapped on the MAF sensor yesterday while it was idling, no response. The engine wasn't that warm yet, don't know if it had gone into closed loop, or if that is even required. I think the PCM reads the MAF even when cold. Then later that day I drove the car 20 miles and the Service Engine Soon light came on, P0401 - EGR insufficient flow. Apparently there can be a number of causes for this; MAP not reading the manifold pressure increase when the EGR opens, no crank sensor signal, even the vacuum solenoid that operates the EGR valve, and of course the EGR valve itself. Although the only one of these the corresponds with they symptom of the engine cutting out is the crank sensor.

I haven't check the ICM connector yet, will locate it in the service manual and check.

Necro alert, you posted this 7 years ago: "Check that egr to lim tube that always has a crack in it around the edge by the LIM. Ok, 80% of the time. Ask me if you don't find a crack and I'll describe better where it's located."

I've had an exhaust leak for years, only when cold. When the exhaust heats up it closes up. Sounds like a single cylinder tick, like you would get from an exhaust manifold gasket leak. Probably unrelated . . .

The right topmost white wire on the Ignition Control Module connector looks severely kinked. I tried to look up the wiring diagram for the ICM connector, but couldn't find it in the factory service CD. Are they not there, or am I blind?

Can't edit posts . . . ?? Another post then: EGR tube isn't cracked, at least the parts of it I can see.

I tried wiggling the wires at the ICM connector, as there appears to be a sharply kinked wire there. This did not cause the engine to stumble or die. I'm not keen on changing out a $220 (online price) ignition module without some evidence it is causing the problem.

At this point the car is not safe to drive. It runs most of the time, but having it die while pulling out in to traffic could be a Bad Thing. But it is too intermittent to troubleshoot in a rational way. I guess I'll start taking the plastic split loom off the wire harness and inspect for breaks or shorts.

I should mention this car has had a very rare electrical issue: the horn will honk on very rarely when going around a corner. I always just chalked this up to an issue with the clockspring under the steering wheel. I did not see it as particularly important on this old car, and left it alone. I'm not sure any engine-critical wiring runs through the clock spring, or if there is any way an occasional un-commanded horn honk could be related to the problem causing the engine to briefly cut out or die.

Are wiring diagrams for this car available? I thought they would be in the Factory Service Manual (FSM), but have not been able to find them.

A clone Tech 2 scanner will be here Friday. I can use this for my 2009 Cadillac CTS as well, so it is easier to justify the cost.

A CKP re-learn will be performed. If this does not help with the cutting out problem, and my guess is it probably won't, live monitoring should be useful to help narrow down the source of this intermittent problem. It will usually fail briefly once or twice in a ten minute drive, so having a Tech 2 set up to monitor some key signals should help.

If the wires to ICM are in poor shape, the you likely just need the harness. It's $90 on Amazon. I had to replace mine a few months ago. Link is below. If you're gonna replace the ICM itself, or the coils, hit up a junkyard. That's the consensus around here anyway.

Amazon.com: Dorman 645-688 Engine Camshaft Position Sensor Connector: Automotive

From the research I've done, a bad ignition switch on these cars can cause all kinds of strange things to happen. Reading about the horn hoking made me think of that. Lights not turning ON, lights flashing, radio ON & OFF, interior light issues, car stalling momentarily. All these strange symptoms have been attributed to a faulty ignition switch.

Originally Posted by CHI2000GTP

If the wires to ICM are in poor shape, the you likely just need the harness. It's $90 on Amazon. I had to replace mine a few months ago. Link is below. If you're gonna replace the ICM itself, or the coils, hit up a junkyard. That's the consensus around here anyway.

Amazon.com: Dorman 645-688 Engine Camshaft Position Sensor Connector: Automotive

From the research I've done, a bad ignition switch on these cars can cause all kinds of strange things to happen. Reading about the horn hoking made me think of that. Lights not turning ON, lights flashing, radio ON & OFF, interior light issues, car stalling momentarily. All these strange symptoms have been attributed to a faulty ignition switch.

You're points are all valid. Thanks for the link to the harness, it is an inexpensive repair - if that is what the car needs. I think a fault in the harness can be found monitoring the crank and cam position sensor outputs with the Tech 2, so this doesn't need to be a guess at a repair. I'm not sure if the Tech 2 will aid in diagnosis of an intermittent ignition switch. One would think it could notice the "key" switching on and off, I guess I'll find out. Wiggling the ignition key has not produced any clues, but that isn't where the electrical switch is located.

Some quality time with the Tech 2 plugged in live showed the MAF maxing out, then falling to zero when the car stumbled under acceleration. Finally set the P0102 code during these events, like it couldn't have done that before I bought the Tech 2. Good tool to have, though. Ran the CKP relearn too, although this had no effect on the engine cutting out.

Any troubleshooting suggestions before I drop nearly $200 on a GM MAF for this car? I unplugged the connector and didn't see a hint of corrosion thanks to good ol' weatherpak seals. I know it could possibly be a wiring problem, but given the intermittent nature I don't think ohming out the harness with a multimeter is going to tell me anything. I'll be disappointed if I change the MAF and the problem is still there.

I guess I should go drive it around after reseating the connector.

Replaced the MAF with an OEM unit. Not only did the intermittent cutting out problem disappear, but it runs smoother now!