2010 YUKON DENALI CODE P0304

[David Ott]

Misfire code for cylinder 4, (#2 on right side), replaced spark plugs, cylinder 4 plug fouled out. Cleared codes, P0304 came right back. Removed plug, found some debris on plug, disconnected coil, started engine to blow out any contamination, checked compression, 110lbs, reinstalled plug, code came right back. Swapped cylinders 1 and 4 coils, still have P0304, swapped cylinders 1 and 4 plug wires, still have P0304, and it comes back within 30 seconds. I would think, if I had a bad injector on cylinder 4, I would get a code for an injector, not a misfire code? Added over 10 gallons of Shell Premium, and a can of 44K, drove truck for at least 25 miles, clearing codes each time it set, to no avail, but it was taking longer for the code to set, close to a minute. Each time code is cleared, once check engine light goes out, truck clears out and runs okay, then starts to miss and resets the code. Any ideas?

 

[swathdiver]

What kind of debris? Compression seems low, did you check the other cylinders to see if there's a variance between them and #4? This is an AFM cylinder. Do you have access to the shop manual via AllDataDIY and an advanced scan tool like the Tech2? How about one of those little usb bore light camera to look inside the cylinder? Have/can you perform a Crankshaft Position System Variation Learn procedure?

@randeez

 

[gpracer1]

I would hope to see at least 150 with all plugs out.