08 hummer h2 misfire

[afatouraee]

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 .

 

[alrock]

How do you know it's on cylinder 7 if you're not getting a code?

 

[afatouraee]

How do you know it's on cylinder 7 if you're not getting a code?

thanks for the reply. i can see it in the scanner in misfire count. no other cylinder has miss fire and it is only on cylinder 7. spark plugs and wires are new. coil is new i even swapped ignition wire and plug with other cylinder to make sure they are not defective. same i swapped injectors also with other cylinder. i think the misfire number has to be in thousands for it to through check engine light.

 

[apollo18]

thanks for the reply. i can see it in the scanner in misfire count. no other cylinder has miss fire and it is only on cylinder 7. spark plugs and wires are new. coil is new i even swapped ignition wire and plug with other cylinder to make sure they are not defective. same i swapped injectors also with other cylinder. i think the misfire number has to be in thousands for it to through check engine light.

hmm swap coils and wires with a known good cylinder. get someone to rev the vehicle and see if you notice any odd noises when you are in the engine bay area. lastly try a brand new fresh plug in cylinder 7. other then that not sure what it could be. it could be intake gasket etc.
i would do a leakdown test and maybe if you can look inside the cylinder with those cameras
chceck the fuel injector again and make sure the plug wire ohms are good

 

[Dgez]

thanks for the reply. i can see it in the scanner in misfire count. no other cylinder has miss fire and it is only on cylinder 7. spark plugs and wires are new. coil is new i even swapped ignition wire and plug with other cylinder to make sure they are not defective. same i swapped injectors also with other cylinder. i think the misfire number has to be in thousands for it to through check engine light.

Hi
Did you mange to fix the problem? If yes what was the problem
I have the same issue with my 2008 H2
Thanks

 

[Exodus]

i've had the exact problem on older gas fired engines, installing supposed better then OEM plugs. which ran great for a little while and then mis fires

since then i've rarely used non OEM plugs

 

[Big2dabank]

Did you check the knock sensor? I have had to replace those a time or two?