Backfiring, 454TBI

87crew4x4 · September 9, 2006

I am not sure what to think, It runs fine, for say, the first 20 minutes as soon as the temp gauge hits operating temp 185ish or so, (instant piece of junk) severe backfiring at part throttle. I had replaced the distributor 4 months ago due to its age, I am pretty certain that it is in correctly (not a tooth off) ("maybe") timing light shows good, and it runs fine until warm. in fact it ran fine all weekend camping and then the second we hit the valley floor it started again.

I know there are temp switches and vacuums, but where and what exactly i am not sure. What does the computer change at operating temp? It does not act like an egr problem (idles fine and runs good other than backfire). I know its old and most of you guys have moved on to the next century and all but I really need to keep her running. Thanks for any help you can provide, even if you are just thinking through it share with me maybe its the right direction.

(Throttle Pos. switch seems fine) already checked,( besides only has trouble when warmed up) Coil, Dist, pickup and spark control all new,

It seems to be worse at about 1/3 throttle only when it hits operating temperature.

Thanks again.

Charles Salt Lake, Utah

2500HD4X · September 9, 2006

as soon as the temp gauge hits operating temp 185ish or so, (instant piece of junk) severe backfiring at part throttle.

Well man, I feel your pain, I still haven't gotten mine figured out. I am fighting an 88 TBI problem....

I don't know exactly what could be causing your backfiring, but from doing a lot of research trying to figure mine out, I know that the ECM goes to completely different parameters for the engine when it warms up and goes into "closed loop" mode. Most GM's have a 195 thermostat in them, so that would be about where it swaps up to closed loop mode and your problem occurs....

Is it giving you a service engine soon light when this happens? Or just hiccuping/backfiring? If its giving you an SES, at least you could pull the codes and get a place to start diagnosing....Probably not much help, but good luck with it!

desrtrat · September 9, 2006

only back fires at operating temp, i would say check all your vac. lines. there use to put the vac. diagrams on the fan shroud. if not get it up to temp and take a can of carb. cleaner and bring your rpm's up to about 1500 and spray ALL the lines/fittings. you don't need to spray much, just a little, and listen for any rpm change. also intake manifold. and TB

OLD SCHOOL...there use to be a vac. switch on the therostat houseing, i think there was 2 lines comming off of it, and one in the intake manifold, and one in the air cleaner. more of a vac. motor than anything. if all checks out good then i would do a compression test in it, BUT i think you will find it to be a vac. issue..

hope this helps, i'm not good with a key board so i hope this helps.....

good luck