1994 gmc k2500 5.7 tbi \auto \111k

[mike426]

the problem im having with my truck ,is when the truck warms up[only when its warm], when u put it in gear reverse,or drive and hold your foot on brake,like at a stop light the truck takes a few seconds but then starts to miss,shake goes away for a couple seconds and then keeps on doin it but never stalls,it wont do it if its in nuetrual or park. when i go to take off with truck from a stop, is starts breaking up,pooping and backfires a couple times but then clears up higher in the rpms and then drives fine until i go to floor it again or come to stop, no smoking and oils clean and oil press is 40-45psi

i replaced so far and no changes
new gas tank\no dirt or rust
new fuel pump,screen[filter in tank]
new inline fuel filter 3times in past month\all new gas lines
cut catalyic converter out and put stright pipe\brand new muffler
new spark plugs
wires/almost brand new
new cap\rotor
new map sensor
new egr valve\cleaned out manifold where sets in
new egr valve selonoid
rebuilt tbi [all new gaskets]also trhottle body base gasket
new pcv valve
new coil
replaced ground from block to frame\was broken
new idle air control sensor
new coolant temp switch
replaced all new vacum lines on manifold/thottle body

[2000CAYukon]

Originally Posted by mike426

the problem im having with my truck ,is when the truck warms up[only when its warm], when u put it in gear reverse,or drive and hold your foot on brake,like at a stop light the truck takes a few seconds but then starts to miss,shake goes away for a couple seconds and then keeps on doin it but never stalls,it wont do it if its in nuetrual or park. when i go to take off with truck from a stop, is starts breaking up,pooping and backfires a couple times but then clears up higher in the rpms and then drives fine until i go to floor it again or come to stop, no smoking and oils clean and oil press is 40-45psi

i replaced so far and no changes
new gas tank\no dirt or rust
new fuel pump,screen[filter in tank]
new inline fuel filter 3times in past month\all new gas lines
cut catalyic converter out and put stright pipe\brand new muffler
new spark plugs
wires/almost brand new
new cap\rotor
new map sensor
new egr valve\cleaned out manifold where sets in
new egr valve selonoid
rebuilt tbi [all new gaskets]also trhottle body base gasket
new pcv valve
new coil
replaced ground from block to frame\was broken
new idle air control sensor
new coolant temp switch
replaced all new vacum lines on manifold/thottle body

1st of all, welcome to this forum. Lots of knowledgeable folks on here.

2nd, hows the weather these days in Wappingers Falls? I use to live in Poughkeepsie 30 years ago.

Looking at your list of replacement parts, I don't see 02 sensor which may or may not be related to your issue.

I am having a similar issue on my 90 GMC K1500. What I think is happening is that the ECM thinks your truck is running rich (due to rings, valve guides and/or valve seals, or 02) and leans out the mixture. The problem is that it is not really running rich so when it leans it out, it actually leaned it out too much (backfire is a good indication of this) and the truck runs like crap.

Again this is only my theory at this point. I felt the issue was more ignition/ecm so I replaced a bunch of parts (many that needed replacing) only to find that it was not the root cause of the problem.

In my case, I have the blue smoke screen at startup (and only at startup) so I think my issue is valve guides and valve seals. Don't know when I will get a chance to prove this theory but I will be working on this during the spring.

Does yours smoke at startup? Have you done a compression test?

Good luck and if you find anything, please post the results.

//2000CAYukon

[mike426]

thanks for reply ,the truck doesnt smoke at all,and i didnt replace o2 yet i was thinking of doin it but i didnt get around yo yet

[MyTOY]

I could be totally wrong but I thought I read a while back, a bad booster vacuum check valve can cause some probs. I see you replaced the lines.
just another thought. Good Luck