Chasing Issues: P0523, Cyclinder 4, 7 Misfires
 

Hello all and hope you're enjoying the holiday season.

Subruban LT 1500, 5.3 with 230k miles. About a month back, caught a code for cylinder 4 misfire, accompanied by a rough idle. Replaced the offending plug, code and symptoms went away. Plug was borderline, gap looked a touch wide.

A week ago, code for cylinder 7 misfire. Manually cleared it and drover another ~100 miles for a week without symptoms. After a longer trip last Saturday, heard a consistent ping. Replaced the driver side bank of plugs; cyclinder 7 plug was fouled, dark brown and wet. Ping turned into a knock on startup and rises and falls with RPMs. Drove one day, yesterday, and knock persisted. P0523 code presented yesterday, but oil pressure gauge shows within normal operating range.

When I was changing the driver side bank of plugs, noticed a rodent nest on top of the block, in the channel between the head and centerline. Did not observe any obviously damaged wires, but it was late and dark. Unsure if the issues are related. Additionally, it's due for an oil change, at about 4k miles on the current fluids.

Thoughts on how to proceed, what the culprit to could be? No rough idle or misfire codes after changing the plugs out, just the knock. Thank you.