bartonz
TYF Newbie
- Joined
- Feb 17, 2016
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This will be long, trouble some bastard... any thoughts will be greatly appreciated.
Info:
96 GMC Yukon with the vortec pushing 290,*** miles. Many parts have been replaced along with engine rebuild. I have a backfire and shudder problem that arose over summer. On cold start up there is usually an intermittent backfire that won't stop until driven accompanied by a blinking SES. The idle is very rough on start up and the motor is sluggish once in gear and going, I've found that babying it up to ~35 MPH the engine smooths out and it is like the problem never exists. Once the backfiring episode is over there is an idle fluctuation in gear at a stop from 650 to 500 rpms and once it dips there is a shudder. I have noticed this shudder a hand full of times while 65+ MPH but goes away with some gas. I have had nothing but problems with this vehicle from day one. I have done a tune up since the rebuild with AC Delco plugs gapped accordingly, Taylor 8mm wires, Delco rotor, Accel cap (didn't have Delco in stock), MPFI spider update, timing retard set within spec of +/- 2 degrees. Everything under the sun to get misses and BS over with. All was well until the summer.
What I have tried since:
Half bottle of MMO in crankcase for possible sticky valve. Little in gas tank. This quieted up some small ticking and seemed to help the backfire as well but it is still there on start.
Cleaned MAF, IAC, EGR, checked for vacuum leaks didn't catch any.
Really stumped. I plan on changing the cap and rotor again this time all AC Delco and maybe the coil. Heard accel's caps can cause crossfire which could be my whole stinking problem. Again thanks for any insight.
Info:
96 GMC Yukon with the vortec pushing 290,*** miles. Many parts have been replaced along with engine rebuild. I have a backfire and shudder problem that arose over summer. On cold start up there is usually an intermittent backfire that won't stop until driven accompanied by a blinking SES. The idle is very rough on start up and the motor is sluggish once in gear and going, I've found that babying it up to ~35 MPH the engine smooths out and it is like the problem never exists. Once the backfiring episode is over there is an idle fluctuation in gear at a stop from 650 to 500 rpms and once it dips there is a shudder. I have noticed this shudder a hand full of times while 65+ MPH but goes away with some gas. I have had nothing but problems with this vehicle from day one. I have done a tune up since the rebuild with AC Delco plugs gapped accordingly, Taylor 8mm wires, Delco rotor, Accel cap (didn't have Delco in stock), MPFI spider update, timing retard set within spec of +/- 2 degrees. Everything under the sun to get misses and BS over with. All was well until the summer.
What I have tried since:
Half bottle of MMO in crankcase for possible sticky valve. Little in gas tank. This quieted up some small ticking and seemed to help the backfire as well but it is still there on start.
Cleaned MAF, IAC, EGR, checked for vacuum leaks didn't catch any.
Really stumped. I plan on changing the cap and rotor again this time all AC Delco and maybe the coil. Heard accel's caps can cause crossfire which could be my whole stinking problem. Again thanks for any insight.