Have something i have never run into prior-when cold under ANY load it backfires

[stlbob]

well not guessing..lol..i did pull the plugs and they didnt look bad at all.Did a combustion byproduct test it all stayed blue..was concerned i might have had a leaking head gasket that when cold was open and as it warmed it closed..no evidence for that..i dont put down everything i do because a lot of it are things i have done untold times and i just do it.Like sealing off the rad only vent left is overflow have 12lb cap. I t into line with a homemade pressure set up..if i exceed 12lbs when the cap opens i am pressurizing the coolant system from somewhere,BUT didnt have that issue.So tomorrow i am checking for unmetered vacuum leaks..then i will ck for leaks above the throttle plate...far from guessing just a lot of typeing to go thru all i am doing.I will find it,i have never NOT found what an issue is this is just being a royal PITA and i asked here for fresh ideas,things i may have just not thought of.

 

[austinado16]

No need to look for a leak "above" the throttle plate, you already have one.......it's called incoming airflow.

Leaks after the throttle plate are what cause lean running issues, because that is unmetered air (as you know). Those leaks will only affect idle, and won't be noticed when the choke is "on" because of the falsely richened mixture.

"Looking" at spark plugs does not tell if they are performing poorly when cold and under load. So that is not a diagnostic step. I see spark plugs almost weekly, sometimes daily, that "look" great, and spark great, but will either not fire at all under the squeeze of compression, or they fire so strangely under compression that the engines will barely run.....popping out either the exhaust, or the intake, or both.

 

[stlbob]

your right on the plugs but i was looking for some blisters on the porcelain i really think i have a lean issue..so im pulling off the carb and doing a rebuild,its been on 3 years ( cant hurt ) trying to find something that is exposed cold and isnt warm/hot..like today this am its 70 outside hopped in it,let it idle for about a minute and just took off.Jumped on the highway which is like 200 yards from the house and it pulled like a bear..Listen i was NOT
trying to be a smart ass so you seemed to be a little testy ..You dont know me i get that but in St.louis i was one of the best worked my butt off to get good and then this old 91' Burban is kicking my ass,so as the wife is right to point out pride goeth before the fall...or to paraphrase ' Bobby humble remember humble God didnt say the smart would inherit the earth ' ...so if i came off wrong sorry about that didnt mean to i just am a tad frustrated..

 

[Oldrider]

You said the popping goes away after it warms up. Interesting.
I had trouble with my GMC after someone swapped two plug wires while it was parked in a parking lot.

 

[stlbob]

OR like today.Nice 75 and he ran great.Its a heat thing making me nuts.I am pulling the carb off and going to freshen it up and ck for anything that looks at of place.

 

[crazy4offroad]

Have you ran a vacuum test while the engine is cold?
http://www.gmsquarebody.com/forum/showthread.php?t=1570

Have you tried the propane torch trick to try to find a vacuum leak?
http://www.gmsquarebody.com/forum/s...ighlight=propane+torch+vacuum+leak#post105569
Might read the rest of that one and double-check your firing order lol.

You could get out the auto ranging multimeter and check your ignition components. I'm not real familiar with the TBI stuff but this sounds like something a coolant sensor could induce.