2015 6.2 misfire on #8 Help please.

[RayRaysJukeJoint]

I have a 2015 yukon xl with the 6.2. It started misfiring on 8 and so far I have done the following.

1. New Plugs
2. New Plug Wires
3. New Injectors

Still, the misfire is there. I get the P0300 and then the P0308 code and I am at a loss as to what to try next.

Oh and I swapped the coil out with another cylinder and that did not change anything. The only thing I can think of now is the wiring harness and I am not sure how to test those. I can figure out the coil probably but how the heck can I test the injector wiring without taking the intake manifold off again?

Also, I don't think it is the lifter issue because #8 is not a DOD cylinder.

Any help would be greatly appreciated!

 

[exp500]

Do a compression test first, Then put it on a scanner. Report back.

 

[1BADI5]

Could still be a broken valve spring, pretty to check

 

[bob3700]

I have a 2015 yukon xl with the 6.2. It started misfiring on 8 and so far I have done the following.

1. New Plugs
2. New Plug Wires
3. New Injectors

Still, the misfire is there. I get the P0300 and then the P0308 code and I am at a loss as to what to try next.

Oh and I swapped the coil out with another cylinder and that did not change anything. The only thing I can think of now is the wiring harness and I am not sure how to test those. I can figure out the coil probably but how the heck can I test the injector wiring without taking the intake manifold off again?

Also, I don't think it is the lifter issue because #8 is not a DOD cylinder.

Any help would be greatly appreciated!

I second the compression test as ultimately, it could be a broken valve spring or a burned valve!

 

[RayRaysJukeJoint]

Update. I was going to do a compression check as exp500 suggested but I do not have a compression tester and I decided that I was getting in over my head. I mean that I dont think I would be willing and able to complete any work that would be indicated by low compression... and as it turns out I was right. I took it to a good shop and then found low compression on 8 and determined it was the head gasket by pressurizing the coolant system. Anyway, they are pulling the heads and replacing the head gaskets so we shall see if this does the trick.

Thanks for the help guys and sorry for getting back to you all so late.

 

[Boatguy272]

what is the mileage out of curiosity ?