Just thinking out loud here. I've had brand new spark plug wires out of the box that did not have good spark plug retention. Even though it clicked onto the spark plug tip all the way, if I wiggled the wire, I could feel that it was actually loose on the tip of the plug. It's happened to me more than a few times. Now I check every time to make sure it clicks and is actually tight on the plug. Chasing your tail sucks bigtime when you fix one problem and unknowingly create a new problem.

 

Not necessarily...if the MAF readings are within spec it may still be bad and not throw a code. Easy enough to swap in another MAF (if you have access to one), or disable the MAF with tuning software and run speed density...

Since it's an intermittent problem, I'm leaning more toward an electrical issue than a mechanical one, even though there are no codes...possible intermittent open circuit or open ground? How about throttle body/TAC module, anything that you can monitor with scanning software...while the problem is happening?

 

I kind of think its a faulty injector. Even if the impendence is on (what tech2 checks), they could still not be fully functioning. Do you have another set you could swap in? FIC can test yours for you...

 

Sorry Bill, thanks for the reply, but no MAF here.

 

Thats also on the list of things to check. If i pull the injectors they're getting sent to FIC to be tested, etc.

 

I had an 05 Silveraldo kick my butt with this issue. Root cause was a gauled up lifter. It would missfire when the roller on the lifter rolled into a bad spot and not miss when it was on a good spot. My thoughts is to pull the heads and check lifters.

 

Do you still have egr? If your valve is hanging open it will cause backfires and mimic a vacuum leak....

 

Did you figure out what caused the lifter to get messed up in the first place? Was it throwing any misfire codes? How many miles did you have at the time?

No EGR on my '03

 

I mean who would think a bad lifter would work sometimes and not others. Holy crap, that would suck.

 

This is a strong possibility also, and from what I've seen, faulty/clogged truck injectors are fairly common. I've seen pics of lifters with this rusty looking gunk in them, either completely or partially clogging the injector.