5150mechanic

iTrader: (6)

Hey guys , finally had to go to the keyboard for some ideas on this one. Here's the case. 2005 yukon lm7 120k. Cold start it starts and idles great. Once it gets to operating temperature it forms a mis on #5 at idle. Off idle it disappears. No mis under load, cruising, or full throttle. The last 6 feet coming to a stop you feel the yukon chugging almost like its loping , a real shitty feeling like its trying to push thru the brakes. No codes present , passed smog, but counts up misfires on #5. What I've done so far; acdelco iridium's, red acdelco wires, flip flopped coils, intake gaskets, another gm intake, replaced injectors, cleaned tbody and maf, crank relearn. I thru the parts at it cause they're typical and I'm time limited. If the gov. makes us shut down then I can get into the lifters, cam or maybe do a 6.0 swap. I'll go ahead and do a compression test and leak down this weekend. No ticking, at least nothing I can hear. Any values I should look at on the scanner? If #5 is low thru the rings I guess I call lkq. Thanks in advance for thinking on this one.

G Atsma

Sounds like a valve slightly hung open, possibly a lifter plunger stuck at the top of its travel. Or a slightly burned valve.
Do a compression check and see if #5 comes up short.
I'm in central Calif. too, in Hanford. Where are you?

5150mechanic

iTrader: (6)

I'm a little north of you in Modesto. That was my next move maybe this afternoon or in the morning. I forgot I did cut that injector off with the scanner and it did make a difference. That lobe or lifter is probably trying to go bad.

G Atsma

Unless it is totally gone, a bad lobe lobe won't show as a miss. It just won't open the valve as much. That's why I'm thinking burned valve or stuck lifter plunger. A small compression leak hides once revved up.

5150mechanic

iTrader: (6)

Higher idle when cold would cover it up, even a ring issue.