hi everyone, i have a 2008 hummer h2 sut that has a misfire on cylinder 7. it’s not enough to through a code but when idling or cruising at highway speed with low rpms around 1500 i can feel the misfire and the car feels like sputtering but when i press the gas pedal it goes away. i have changed the spark plugs, wires and put a new coil as well still same issue. did compression test and it has same compression as other cylinders. i did replace the injector with another cylinder and still no difference. the fuel pump is new and pressure is within factory specs.
i’m truly puzzled and any help will be appreciated .

 

I have an 07 SUT and had the same issues with 7 & 8 coils. I replaced ALL of the coils, because when 1 goes they are all probably going to go eventually, as well as the plug wired AND the coil harnesses. The harnesses looked okay but changed them out anyway. That fixed the issues. Hope this helps you!

 

I had same issue with my 08. I had to change the Phaser, oil solenoid and magnet sensor. After replacing these no more misfires and mine didnt throw a code either. The timing belt cover needs to be removed to replace these parts. BTW, the new oil solenoid has more holes for the oil flow than what came oem on the H2. I guess GM knew they made a mistake with the original part and changed it now.

 

intake or exhaust manifold leaks can also trigger misfires as well as the solenoids in the intake valley. also do you notice a ticking coming from that area of the engine? could be stuck lifter or exhaust manifold Leake due to broken bolts.

 

thanks for your reply. it has new headers, gaskets and header bolts. no intake or exhaust leak. i did a compression test and compression is same as other cylinders 145-150.

 

thanks for your reply. is it a possibility for you to explain more or provide me with part numbers. many thanks

 

these are the 3 things I had my friend who is an awesome H2 mechanic change out. He figured it out and since changing these parts if I go 70 mph I’m getting over 13 miles a gallon. If I do 55mph I was getting 18 average on highway. Hard to believe but before changing out these parts I would only get 8-9.5 mpg on highway.




I went all AC Delco, you can call any GM dealership and get the part numbers. Only the phaser I listed is the actual AC Delco part.