P0308 Misfire Code while road tripping

[wjburken]

Ran seafoam through the TB and drove her hard as recommended for 10 minutes. CEL came on blinking after 300 miles on return trip. 41k miles. Checked the code and it was a missfires on more than cyl 8 now. Leaving to move and need to trailer with the suburban so took it to the dealer to let them dig into it. DID NOT MENTION SEAFOAM TO DEALER.

They found nothing in their diagnostics and want to do a $485 fuel rail and TB flush (much higher concentration than seafoam and requires an oil change). I said it sounds like a powertrain issue with that approach and they said not yet. The counts they showed were:

cyl 5 364 mf
cyl 7 590 mf
cyl 8 1040 mf
cyl 3 22 mf
cyl 6 15 mf

I am unsure of how long the tech ran the car and in what rpm to get these numbers.

Freaking out a bit because I gotta leave the state and need to take this car - I think I might wait until I reach my destination to do such a flush.

Thoughts?

What is the condition of your plugs?

 

[swathdiver]

Ran seafoam through the TB and drove her hard as recommended for 10 minutes. CEL came on blinking after 300 miles on return trip. 41k miles. Checked the code and it was a missfires on more than cyl 8 now. Leaving to move and need to trailer with the suburban so took it to the dealer to let them dig into it. DID NOT MENTION SEAFOAM TO DEALER.

They found nothing in their diagnostics and want to do a $485 fuel rail and TB flush (much higher concentration than seafoam and requires an oil change). I said it sounds like a powertrain issue with that approach and they said not yet. The counts they showed were:

cyl 5 364 mf
cyl 7 590 mf
cyl 8 1040 mf
cyl 3 22 mf
cyl 6 15 mf

I am unsure of how long the tech ran the car and in what rpm to get these numbers.

Freaking out a bit because I gotta leave the state and need to take this car - I think I might wait until I reach my destination to do such a flush.

Thoughts?

We used to hook a can of Echlin up to the fuel rail and let the engine run on that until the can was empty. That was GMs fuel injection service way back when and they still sell it.