the main prob is that its not my truck. its my brothers. i only get it for a couple hrs 1 wknd a month. its his only transportation. once the throttle is tapped, the misfires stop completely no matter how long the engine is running. you can shut it off, let it set for LITERALLY 1 min, fire it up, it runs fine until the ecm goes in2 closed loop then starts misfiring, tap the throttle and the engine runs normal.

 

Sounds like a non-issue then, if simply tapping the throttle solves the problem..... you could spend a lot of money trying to solve that one, and its rather a minor annoyance.

 

is it poss that once the rpm's return to idle, the ecm adjusts the pulse width modulation of the injectors to compensate for a small vac leak caused by the plenum gasket? because it will stay running just fine only after the throttle is tapped. it will ONLY misfire if the engine is shut down, restarted, then go into closed loop.

 

Does it still miss while driving and the rpm's fluctuating, or is a tap of throttle "needed"?

 

no misfire @ idle OR in gear. it requires a tap of the throttle to make it stop misfiring. once the engine starts to misfire, tap the throttle, misfires stop completely for as long as the engine is running.

 

what im not understanding is that if it WAS the plenum gasket suckin air, shouldnt it misfire all the time & not b temporarilly cured by tapping the throttle? once the rpm's come back down after the "tap", it runs fine.

 

What I'm trying to say is, is the tap required or when it is missing, can it be put into gear and driven, and the miss goes away or does it stay until a tap is made?

Me getting confused.

 

my MasterTech scan tool shows no misfires while driving down the road @ any speed or rpm. the misfires immediately start once the ecm switches from open to closed loop.

 

the misfire will stay when its put into gear. the misfire will go away once the rpm's increase. if its in park, the tap is required to make it stop misfiring.

 

The engine creates greater vacuum at lower RPM, so it makes sense that tapping on the throttle, thus decreasing over all vacuum would stop the miss fire. I am leaning heavily toward vacuum leak now. AS THE CRANKSHAFT TURNS.............