94 Jimmy, 4.3 with CPI, wont idle cold

[SlugHog]

In May of 2007 I had replaced the CPI and the Jimmy had been running fine until it got really cold here. I am in central Alberta, Canada. The Jimmy would start fine, idle for about 20 seconds, then extremely rough, then stall. I would then start the truck again and would more or less repeat the scenario.

I dropped the Jimmy off at my mechanics shop and the only thing they could determine is that it is running very lean and off the computer when cold. They tried heating up all pertinent sensors and could not find what is causing the problem. They found that if I were to use the block heater, then it would start and idle fine. Having access to power for the block heater is not always available. I should note they also checked to see if it was the computer, fuel pressure, and voltages where applicable.

So here I am asking if any of you fine folks have ever had this problem and if so, is there a fix.

Hoggy

[old_master]

If it were igniton related, it would run rich. Yours running lean, I would check the fuel pressure first. Key on, engine off, fuel pump running, must be 60 to 66psi. Pressure must remain above 55psi for 3 to 5 minutes after the pump shuts off. Post your results.

[SlugHog]

They had already tested for that even though I had replaced the fuel pump and filter back in May 07 when I replaced the CPI.

Hoggy

[Chris Stewart]

Try putting it in gear during the good 20 seconds and see if if the motor dies before the 20 seconds are up...I'm just guessing a sticking Idle Air Control Valve(IAC).

[SlugHog]

Just tried what you had suggested, other than the engine revving up for about 5 secs, it then proceeded to stall again. And it did idle for a total time of approximately 20 seconds.

Hoggy

[SlugHog]

Well I confirmed with my mechanic just now that everything you had suggested was already tested or done. My mechanic believes it to be the CPI and that the cold is somehow causing it to fail. I have ordered a replacement CPI from a company in California which has no way to test my current CPI at -28C, -22F. And yes, we have had a few nights much colder, then factor in the windchill.....

Will let you folks know how I make out but if you have other ideas on what could be the problem, keep them coming.

Thanks in advance and Happy New Year

Hoggy

[Chris Stewart]

Does the oil pressure show good while the motor is running....seems like there's an oil pressure requirement but I may be wrong, what do you remember about that OM?

[old_master]

Chris, I think you're right, 94 does have the fuel pump circuit in the oil pressure sender, but it's a redundant circuit. Losing it will not cause the fuel pump to quit, if that's what you're thinkin'. Not quite sure why GM did it that way. When the engine is running, two 16ga wires are used to power the fuel pump. By using 2 wires the same gauge, it doubles the load carrying capacity of each wire, why not just use one larger wire??????

I've seen it where the electrical connector at the CPI gets loose, I suppose that's a possibility.

[SlugHog]

It appears the culprit was indeed the CPI. The only thing I can conclude is that when it gets really cold, some part is contracting and restricting movement inside the injector. But all now is well. I thank all for their input....

Hoggy

[old_master]

See post #8, the connector to the CPI has been a problem in the past. It tends to do exactly what you suspect, contracts when cold, and opens the circuit.

[SlugHog]

That was checked originally as my mechanic has seen that happen, more on Dodge trucks then GM's, but was aware. I am just happy I am no longer restricted to going to locations where I have to plug in my vehilce if intend on spending any time there.

Hoggy