Question : 2.8 Stall

[89Hatchback]

Oh great. A new problem in my daily driver. Driving home late last night, the engine started bucking and then stalled. I rolled over to the side and stopped. I was able to re-start with no problem and slowly drove away with no problems, but as I picked up speed on the hill it started bucking again.

When I say "bucking" I mean the engine just died for a split sec. The tach would dive toward zero and then it would just resume again. This occurred about 10 minutes into my trip and continued for another 5. Once I got to the top of the hill everything was OK, and I drove another 15 minutes with no problems.

I'm not sure why things were OK after that. It was a humid night, but no rain or puddles anywhere. My only guess is this is a long steep hill where the RPMs climb the highest - up close to 3000 RPM. The rest of the trip is nothing close.

I replaced the crank sensor just a few months back (see my other messages for that adventure). I did notice the insulation on the wiring was cracked when I was done, so that's a concern.

My question is what are the likely suspects? If I remember correctly, it's the crank sensor, the ignition module and the ECM all all possibilities. Since the engine is running now, there's no tests I can do to find it. I did check for codes, but none were set.

[WrathOfSocrus]

No. If it was stalling out as u hit the bottom of an incline then it was likely fuel. The usual culprit is the fuel filter. It's the cheaper of the two to replace anyway. If that doesn't do it then it is likely the fuel pump. I've seen it happen on both carb and fuel injected setups where it would run like a champ on flat ground but any incline and it would sputter just like you described.

[89Hatchback]

The cut in/cut out seemed too clean for fuel starvation. It either ran or it didn't. No stumble. It seemed more electrical, as if I cut out the ignition. Ugh. I guess I can added ignition switch to the list.

The fuel pump was replaced not all that long ago. But it's probably time to change the filter on general principle. Can a clogged filter cause cut-outs that clean?

[jmgtp]

I'd disagree that it is fuel related and say that you hit it right on the head with the CPS or CPS wiring.

Here is why:
If the fuel was cutting out intermittently the rpms would drop and the tach would reflect that drop, BUT if the tach is seriously plummeting along with the engine cutting out and spontaneously jumping back up it is because it lost the CPS signal. You even mentioned you noticed cracked insulation on the wiring.

This happened on my car a few years ago and it too was failed CPS wiring. I'd start there for sure. The GM manual indicates you need to braid the wiring to shield it from electrical interference. I believe it calls for no less than 9 'twists' per foot.

[89Hatchback]

This happened on my car a few years ago and it too was failed CPS wiring.

How did you fix it? I'm wishing I could just buy a replacement cable and skip the harness.

[jmgtp]

A lot of the weather-pack connectors come apart and you can repin them - I don't remember if that is the case with the CPS though. I've done it with the TPS.

It's been a few years since I replaced it, but I believe for mine I cut the wires and left a short lead on each connector to solder in new wire. Should work ok pending your faulty wiring is not in the first few inches of each of the connectors. If it is then you'll have to repin with new wire or find replacement wiring with the connectors already on it.

I wrapped the one I made in the self adhesive wire tape that factory harnesses use and then ran that through a length of heater hose for an additional bit of protection. I ran it from the CPS right to the ignition module with a few securing points inbetween.

[89Hatchback]

Yup. It's the wiring. 1 ohm? I don't think so.

Now I have to figure out how to bandage it up until I can get the pigtail to fix it right.

[89Hatchback]

Got something wedged between the wires, so hopefully that holds until the pigtails arrive. No one in town stocks them.

Off hand, does anyone know if the CPS is polarity sensitive? Because of the loss of insulation, I'm not sure if I'm going to be able to get the same wire to the same terminal. Not a problem if it's not polarity sensitive.

[bszopi]

No, but it does have to be twisted a specific amount! 9 twisted per foot, minimum.

[89Hatchback]

I wrapped the one I made in the self adhesive wire tape that factory harnesses use and then ran that through a length of heater hose for an additional bit of protection. I ran it from the CPS right to the ignition module with a few securing points inbetween.

What kind of wire did you use? I was looking to use some microphone wire I have, but it's only rated to 75C. Just automotive wire is easy to get, but I'm not sure about automotive grade shielded. Is your replacement harness shielded? I know the original one is.