2000 GMC Jimmy SLE- misses under light load when COLD

Hey Guys-

My Jimmy misses under light load when its cold...

It only got bad enough for a random misfire code once, and I ran a can of Seafoam in it, and its been much better....but it still does it....only when cold...

I'd suspect the ignition system, but the temp affect makes me suspect the fuel system...

Any experiences to share?

Hey Guys-

My Jimmy misses under light load when its cold...

It only got bad enough for a random misfire code once, and I ran a can of Seafoam in it, and its been much better....but it still does it....only when cold...

I'd suspect the ignition system, but the temp affect makes me suspect the fuel system...

Any experiences to share?
Good secandary ign?
How long or how many miles since good ac delco tune up?
Fuel pressure?
Any other codes?

The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.

Hey Guys-

My Jimmy misses under light load when its cold...

It only got bad enough for a random misfire code once, and I ran a can of Seafoam in it, and its been much better....but it still does it....only when cold...

I'd suspect the ignition system, but the temp affect makes me suspect the fuel system...

Any experiences to share?Yes I had the EXACT SAME IDENTICAL PROBLEM. READ THIS THREAD:
http://www.automotiveforums.com/vbulletin/showthread.php?t=975186

Don't let anyone fool you. Ac-delco parts only! Anything else is a waste of time and money.

Thanx for pointing me to that thread, Rick! I could have written it myself word for word....

This truck is new to me, so I don't know what ignition parts are on it now, but you can betcher ass I'll be replacing with AC Delco....

Thanx again...you guys are awesome!