Mysterious condition????????????/

[Morphius]

Ahhh, I need some help.

Condition best described: It only happens when the car has set and cooled totally down. Such as the next morning. Ambient temp below 30 degrees. Happens every morning now that winter has set in here in Michigan. The car is started and it runs very ruff. Best described as unplugging two plug wires. It will run like this for a period of time. It differs everytime. Sometimes 10 seconds, sometimes 2 minutes. Then, like it never happened, it starts to run normal.

ECU scan shows nothing wrong. To quickly, root cause the issue I've changed the ECU, Fuel relay, Power transistor, and coil pack. (all out of another running car) Thought process here is to change most everything elecritcal or fuel related and root cause it later when it's warm. I'm in the process of changing the CAS, throttle body and potentially the fuel pump. I might also change the air cleaner assembly also.

I ran across an artical some time ago about a mysterious electrical clitch that happens on DSMs after cool down. Upon restart, it runs ruff for a period of time, as I described, then "fixes" itself after a period of time running. But, I don't remember where I saw this. Has anyone had this condition?

 

[turboholic]

-I would suggest you check the coolant temp sensor, for the ECU send more fuel when the motor is cold but it doesn't know that if the coolant temp sensor is bad. $.02

 

[Plague]

I had a similar problem. My car thought that it was starting and running at its coldest tempuratures. I had changed the coolant temp sensor with no results, shot it down to the ECU contacts. Make sure the pins to the ECU are making good contact. Ran like a champ afterwards.
Good Luck...

 

[Morphius]

I haven't checked the coolant sensor, but I never have issues when it's hot. Only cold.

Where I'm at now:

Again, ECU scan shows nothing wrong. I've replaced the following from a running car:

ECU
Fuel Relay
Power transistor
coil pack
plug wires
Complete fuel rail (rail, injectors, regulator)
Throttle body

Things yet to try:
Plugs
Fuel pump
Air cleaner assy (airflow meter, IAT)
CAS

Can anyone tell me the tell tale signs of a faulty fuel pump? (short of it not running of course) I don't have a fuel pressure gage to check it.

How about a symptoms of a CAS going bad?

The car will set a while and you key it on, it'll start and run for a short amount of time, just fine. It runs 30 sec or so and dies. You try to start it and it acts like it's going start but is firing on 2 cylinders. Not quite enough to start.

Yes, I could systematically go through the book to root cause this, but someone at some time must have had a similiar situation that could save me some time working on this. (its cold out there!!)

Anyone???

 

[Doug99RS]

I see you said you swapped out wires but what about plugs? Frequently spark plugs act up when cold, wires when hot. I'd double check the gap on them as well if they are new/known good.

The engine coolant temp is also a good suspect. If the engine doesn't know what the engine coolant temp is at start up then it won't know which fuel trim to put it in to at start up.

Typically if a fuel pump that is not totally dead, then the symptoms of it dying normally only exhibit themselves at wide open throttle or as I experienced this week, when turning. When it starts to go out, it typically won't be able to supply enough fuel for WOT pull. But it will supply enough fuel on casual driving. Also, fuel pumps that are on their way out will get worse once the pump has run a while (after the engine warms up and you're half-way between BFE and Nowhere, which happens to be too far from civilization).
Doug

 

[Defiant]

Yeah, I would have started with the plugs and wires.

 

[Morphius]

Thanks for the input guys.

Order of what I'll try next:
Plugs
Coolant temp sensor
Fuel pump
Fuel filter
Air cleaner assy.
CAS

Short of that, I'm not sure what else could keep it from running. I just hope that one of those fixes it and it's not some sort of wiring harness short. Chassis has 189K on, so it's possible.

As a side note, I do recall lately i've had a number of WOT "back fires" (as if running lean) or half throttle "bog". I wrote it off as the cold causing Fuel cut of sorts with my boost set at 14-15psi with a MBC. Now that I think about, and after you'd mentioned it doug, maybe my pump is bad. Wasn't my first thought as I replaced it just 2 years ago, or 30K miles. Hmm, maybe I should start with the pump tommarrow.

 

[Doug99RS]

I would strongly recomend more diagnostics before replacing an expensive part like that. A simple fuel pressure check at multiple acceleration points will rule out a fuel pump problem. Plugs are cheaper, easier... and you can still smoke while replacing them and won't spontaneously combust.
Doug

 

[Morphius]

I've parted numerous cars and have an abundance of electrical and fuel hardware. That would include numerous fuel pumps, so it won't cost me anything but the time. In the time it takes to run a diagnostic on it, I can replace it.

 

[Doug99RS]

ok

 

[Morphius]

OK, got the damm thing running. At least the major culprit was the fuel pump. Swapped another used one in for temp, while I go exchange the other. Why couldn't this have happened months ago while it was warm?

Now I just need to work backwards through all the other parts I installed to be sure something I already changed didn't have issues also.

Thanks to all who replied for the help!!!!

 

[Doug99RS]

Glad you found the problem and even more pleased to see you share the solution with everyone.
Doug