I have a 1990 gmc seirra 1500 4X4 with the 5.7 350 in it....im having trouble with it missing and backfiring thru the intake after it warms up...it runs fine cold....i 've replaced the plugs , wires , cap , button , and fuel filter and the fuel pump is about three yrs old...any ideas or experiences?

the EGR device is a pleasant little device what makes the car take exhaust gasses into the intake on DECEL that is when it is supposed to activate, but it has a filthy dirty job snufflin' these gasses to and fro, and so it gets broken in the halfway point and causes bad performance...also may be okay, and working okay but vacuum instructions to do it's job have fallen off, or perhaps the electrical signal to activate the solenoid, or the solenoid itself is bad....take a look at the EGR valve to see it's operation, whether or not it opens and closes alright, and be pleasantly surprised when you've fixed it, was just buggered up with carbon!

your last smog inspection would have spotted this in an instant as the inspection points are 1)smog equipment is there 2) equipment works properly 3) performs satisfactorily at removing smog 4) works okay under all driving speeds and conditions....okay like you'd have gotten as far as point two...it ain't workin' properly~

should have tossed out a CEL (check engine light) on acct of the smog problems~