Cold start problems with 1992 GMC 5.7 liter

[Anchor]

I have tried to find in old discussions anything that applies and can't to this point. Have truck running quite well after a few months of headaches. Suddenly it started running super rough when cold started. I can rev it up for a bit and it straightens out. If I disconnect the wire for timing adjustment up by firewall it starts cold just fine. I assume that it has started wildly moving the timing when the wire is connected. I will put timing light on it when cold but i think this must be a common problem. Any help appreciated. Got to go help wife with sheep but will check in later. Sure would appreciate some help. Thank You.

 

[Anchor]

I can't find this thread in engine performance and maintenance so lord knows where I sent it but will add this anyway. Hopefully someone will find it. "With my computer skills I might as well drive down to the coast and put my question on a message in a bottle. I started the truck this afternoon with my timing light all hooked up with the magic wire hooked up to ecm. I expected it to be retarding but it was advanced way up almost out of sight and flickering. As soon as it smoothed out, about 30 seconds it came back down to around 12 btdc and smoothed out. Taking it for a 40 mile or so drive tomorrow to fuel up ang get some jerry cans of fuel for around the place. Will see if the computer corrects itself. Really need to drive the truck for a bit and see if it smoothes out though I doubt it will without some more tweaking.

 

[WICruiser-97]

Sounds like you initial/base timing is off and it recovers when the ECM goes to closed loop and starts controlling the timing. Try resetting the base timing (wire disconnected) to spec (not sure what it is for that MY).

 

[Anchor]

Sounds like you initial/base timing is off and it recovers when the ECM goes to closed loop and starts controlling the timing. Try resetting the base timing (wire disconnected) to spec (not sure what it is for that MY).

Thank you wic. Set at zero with wire unhooked but will recheck today.

 

[caminonut]

Not sure if this will help your problem, but it sounds like a similar problem I had with mine a few years ago pretty much doing the same thing it turned out to be the temp sensor in the top of the intake not to be confused with the temperature sensor that is in the head.
After replacing the temp sensor, it straightened it right out and it’s been running perfect ever since.

 

[Anchor]

Not sure if this will help your problem, but it sounds like a similar problem I had with mine a few years ago pretty much doing the same thing it turned out to be the temp sensor in the top of the intake not to be confused with the temperature sensor that is in the head.
After replacing the temp sensor, it straightened it right out and it’s been running perfect ever since.

Thank you caminonut. I recently replaced the cts but you know how the new ones are sometimes defective. Will try to ohm it out to check.

 

[Sean Buick 76]

Does the issue persist once fully warm or only from cold to operating temp??

 

[Anchor]

Does the issue persist once fully warm or only from cold to operating temp??

No, does not continue after about a minute or when I goose the throttle a bit.

 

[Anchor]

Thank you wic. Set at zero with wire unhooked but will recheck today.

I should add that the rough running clears up well before it kicks into closed loop, according to my scanner

 

[Schurkey]

First thing I'd do is to connect a scan tool, record any codes that may be present, disconnect the battery for thirty seconds, then reconnect and go for a drive.

I have heard of goofy timing problems getting resolved by temporarily killing power to the computer.