intake backfire 1989 gmc 7.4 tbi

My truck runs great untell it warms up.
Then ( seems intermentent )starts to backfire through the tbi.

Things i had tryed ,
plugs,wires,cap rotor,reman dist.
The only code i ever got was for the tps,replaced it with no change.

any ideas ?

Kelly

Sounds like still a timing issue, distributor in right and timed right ? maybe a bad coil ?

Well I did run the base timing up to 8 btc,calls for 4 btc.
But advancing it helped it not to backfire as much.
Set at 4 btc it will not hardly pull out of the driveway.

panicx

Sounds to me like the distributor is worn out and moving around when it spins, missing the plug wire terminals occasionally when it fires.