Persistent P0307 (also a P0420)

[turbojimmy]

Okay - compression test results on the left bank are:
1 - 180 psi
3 - 155 psi (!)
5 - 180 psi
7 - 160 psi

So compression is okay in the #7. And, the insulator on the #7 spark plug is cracked. I know I swapped that from the #5 a couple of months ago and it did not correct the problem. I'm going to change the plugs anyway. They all looked good with no real difference in color among them.

Falling under the "you can't make this s*** up" category, I changed the plugs and it was worse. Very solid misfire (as opposed to the intermittent one I had previously). Immediate "Service Stabilitrak" and "Stabilitrak Disabled" messages. I double checked my work (even though it's tough to mess up a spark plug change) and it was good. Further investigation revealed no fire from the #3 coil. What are the chances? I happened to have a new one and popped it in. NOW it's 100% fine. No misfiring at all.

So I don't know what started the whole thing. I'm thinking a bad injector. When I swapped plugs between #5 and #7 they were okay but it didn't fix the misfire. Continued driving with the bad injector probably generated a lot of heat in #7 that cracked the plug (and probably cooked my cats). Replacing the injector helped a bit, but the plug was damaged unbeknownst to me.

Now to see if the 420 comes back. It probably will. I'll get to the cats before winter since that's when I'm really going to need the truck.