okay so ive been having weird symptoms now for a while...the cab of my hummer getting really hot on long trips...power loss...a hard jerk randomly when accelerating. so yesterday i was sitting at a redlight and it started idling horribly. rpms dropped..i had to give it gas in order to keep it from dying. so i checked the live data to see what was going on. everything looked good except for my o2 sensor bank 1 sensor 1 kept dropping out to 0 mv...then it would jump back up to normal then fall back out again...but im getting no check engine light. im not sure if i should replace the sensor or what at this point. im not the one to throw parts at a vehicle but without a mil light im at a stand still. im about to check the wiring and go from there. anyone else had any issues like this?

 

#SeaFoamWorks

https://seafoamworks.com/

 

replacing a near 20 year old O2 sensor (and why not all of them) is not a bad investment, bad or cheap sensors dont always trigger the MIL you could test it with a DVOM or swap it with the other bank and see if the readings transfer or stay.

 

Rich conditions can be caused by dirty Air Filters...... easy stuff first. Inspect the Air Filter and wash it if it is a washable aftermarket unit.

Inspect the wires & harness to the O2 sensor.

How old is the sensor, and miles on it?

I just replaced one yesterday on my winter beater, but it was an easy no brainer throwing 5-6 codes for two days and over 100K miles on it. Runs perfectly again. 15 minute job.

 

your symptoms point to clogged catalytic converter. if you have more than 2 psi at the front O2 sensor bung the cat or exhaust has restriction or both if chunks of cat passed through.

 

so not really thinking about coil packs bc this is my 3rd set in 3 years i decided to check the coils with the old water mist trick and sure enough all of bank 1 was arcing not sparking. i know the 6.0s have to have their oem sensors and spark plugs or they'll pitch a fit but has anyone had trouble with aftermarket coil packs? bc apparently this hummer has a hard time with them. i bought some O'Reilly coils just for bank 1 and holy cow what a difference. ive gotten all but 2 out of 8 replaced at this point but this hummer has its good days and bad. never know what mood it'll be in...some days it drives like a dream and then others even with new spark plugs....oh and i replaced the plug wires just for peace of mind...and brand new coil packs im still misfiring on random cylinders. not bad enough to trip the mil but its noticeable...usually no more than 2 or 3 up to 5 misfires at a time. is this just normal? ive been told it is but i dont think misfires constantly are normal.

 

i have 216k miles on my 03 h2 and i do not get random misfires. the coils are still the originals that are pretty heavily rusted. they work fine so no sense in replacing what a'int broken.

 

My 3 had random misfires when I bought it 10+yrs ago. I swapped the plugs and coils due to the previous owner threw generic parts at it. After installing acd plugs & coils, misfires still occurred. I performed an induction service to clear sticking valves. Never had a misfire since!

 

see the thing is with mine is it seems to occur long after warm up. usually sticky valves are more noticeable on a cold motor. i have no misfires on start up...as the temp goes up i get more misfires and even loss of power

 

hot carbon on the valves can cause pre ignition.