Engine misses, occasionally dies, getting worse

[RodBarnes]

1999 Montana with V6, engine misses sporadically and sometimes dies after stopping.

The missing first became noticeable as it was shifting into 2nd. We took it to our usual mechanic and the computer indicated the camshaft sensor was questionable so replaced it. Cleared things up for a few days and then it started happening again.

Things progressively got worse so we took it to the dealer. They were able to experience the vehicle behaving this way but they said the computer registered no error codes at all.

We've had the injectors cleaned, replaced the spark plugs and wires, and fuel filter.

It starts right up in the morning and runs fine but at temperature begins misbehaving again. Warm days are even worse.

It has continued to get worse, increasing in frequency of miss, duration of miss (sometimes it feels like two or three misses in succession), and even to now it dies when we come to a stop. It starts right up but will often die when we put it in gear again.

[Tech II]

Are you telling me, you took this to a GM dealership, the problem occurred for them, and all they could say was:"the computer registered no error codes at all."

I'd call GM customer assistance, and give them a piece of your mind......

[RodBarnes]

LOL. Yeah, that's what I thought. The van is actually my son's (was ours, given to them) so I wasn't there for the conversation or they would've heard from me directly.

My son replaced the plugs/wires and fuel filter before he took it to them. He told me that, without the computer input, they didn't have a clue -- which led them to to the injector cleaning.

[rkvons]

Did the dealer check the fuel pressure when it was misbehaving?

[RodBarnes]

They didn't at that time but it was checked yesterday and found to be normal.

Called the dealership again yesterday and asked about cost of test/replacement of the O2 sensor, CPS, and the PCM. Discussed the symptoms, the increase in intensity and frequency, and what had already been done. The mech was sure that any problem with the O2 or CP sensor would have been registered by the PCM. And that if the PCM were bad it would automatically trigger a check engine light (which has never gone on in any of this, btw). Nor was the mech aware of anything regarding those sensors that could account for missing AND stalling.

So he recommended checking fuel pressure which was done and it was normal. Check off the fuel pump/pressure.

Plan is to take it in and get the CPS replaced. Another post mentioned the MAF with similar symptoms so that may be a possibility.

[JabbaTHutt]

Tell him the next time it happens to get out and take off the gas cap and see if it again starts

[RodBarnes]

Hey, removing the gas cap is great tip - never thought of that.

Here's an update:

• He decided to take it to the dealer again with the intent of having them replace the crank sensor. It died twice on the way, missed repeatedly just as it has been.
• The tech said that just replacing the CPS would be a waste as the PCM checks out as good and it says the sensor is good. So they kept it all day, tested, it drove it, let it sit in the hot sun for 45 minutes and drove it some more --- and never had a single miss or die on them in the entire time they had it.
• Driving it home from the dealer it missed repeatedly (just as it has been) and died three times.
• Out of futility, he just gave up and used it for a minimal trade in on a new van.

Really poor situation. I have no explanation but I guess this saga is over.