ive tried everything, no leaks, new ignition system(coils, plugs etc.) it seems to get worst with high temps, or at operating temp i should say. live data shows 02 sensors and fuel trims perfect. although my evap system is always incomplete. could that be a sign. ive been battling this fight for a year and dumped 6k in it. it seems to just get worst. any ideas guys?

 

have you checked the coolant temp sensor above the #1 plug behind the alternator.
or checked for intake leaks.
or cleaned the throttle body and MAF sensor.
or checked the engine wire harness grounds.
or replace the ignition coil wire harnesses when you replaced the coils?

 

changed the coolant temp sensor, no intake leaks cleaned the TB and MAF 30 times, i even had to change the camshaft position sensor when i first bought it, i didnt do the relearn though and thought maybe it was that, so i did the relearn that literally changed nothing. however i got to looking in the dark last night and all 4 coils on the driver side are sparking between the magnet part of the coil and the coil itself. the passenger side isnt. does that sound familiar to anyone? how do all 4 coils all of a sudden spark at one time in the same place and i was still misfiring before this happened but now the hummer barely runs

 

the cables could be bad the plugs might be shorted or the coils are crap. they do sell GM . acdelco counterfeits of all of them especially on ebay and amazon. buyer beware. they are very convincing fakes

 

well the plugs are ac delco rapid fire i bought from oreillys, the plugs i bought from advanced, they're ac delco, but the coils i bought off amazon, they've been okay for a year now but its just weird all 4 on bank 1 spark at the same time. oh well im replacing the coils and harness

 

still multi mf on all cylinders. not an ignition issue
so an update. bought new stock coils and harnesses and it changed nothing. ive checked o2 sensors and cats and all are running perfectly. it misfires soon as i crank it while cold and while idling or deaccelerating the most ive noticed. 🤦‍♂️

 

Get those crappy #6 ACDelco Rapidfire plugs out. While most part guildes call for them as being compatible (including the ACDelco catalogs), they are terrible in our engines (as well as the 4.8 and 5.3 in the trucks and SUV's). You can find hundreds of posts and reviews on various GM truck forums and retailer reviews on them... one of the most common issues is frequent misfires and overall poor running.

Get a set of ACDelco 41-110 Iridium or 41-962 Double Platinum plugs. Very good chance that if you have those #6 rapidfire plugs, that is why you are having so many misfires. I have the 41-110 plugs in mine (as well as in my 99 GMC, 04 Silverado, and 02 Tahoe).

Also not sure if the 4WD selector switch from a GM truck will work the same unless it comes out of one of the very very few models that are full time 4WD like our H2 (98% of the trucks and SUV's are not full time 4WD). The selector switch in them, physically at least, is different in that the main mode button is 2wd (possible that the buttons are just labelled different though and functionally they work the same).

 

ive looked all over for reviews on the rapidfires. i only got them bc they're the only ones the store had at the time. im going right now to get new plugs but i can tell you that wssnt the issue. i actually fixed the multiple mf on all cylinders. i did the crank sensor variation on it yesterday and so far not one misfire. i thought this procedure had been successfully completed before when i paid a shop $50 to do it. i guess i got stuck with a lube tech doing it bc when doing it with a scan tool you must hold the brake pedal down the entire process. then do a WOT(wide open throttle) and the scan tool cuts the fuel off at 4000 rpms...release brake. done. the shop i took it to just pressed some buttons on their snap on and said it was done. i assumed they knew what they were doing. never assume.

 

Ah - yeah crank sensor off can cause a lot of misfires for sure! Good to hear you got it resolved.