Had a P0304 and a thermostat code for awhile now but never a flashing CEL. Finally got around to new spark plugs and a new thermostat which seemed to have fixed all of my codes until tonight (about 1 week). During my original diagnosis I swapped around the coils to eliminate them and learned that over 1500 rpms the misfire goes away and it only misfires below 1500 rpms after the engine has warmed up. Its also on its second bottle of lucas fuel injector cleaner and a tank of premium. Any help would be greatly appreciated. Thanks!
NEED HELP P0304
- Thread starter killer cougar
- Start date
djthumper
Administrator
Just over 94,000 miles, second owner, standard maintenance, been running full synthetic since I got it with about 45,000 miles on it. First owner was little old lady how serviced it religiously at the dealer. I still have the original sticker that was on the window when it was sold. Didn't change out any of the coil packs, as I didn't think it was necessary since I had swapped them around and the misfire didn't move.
2005 Trailblazer
2005 Trailblazer
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Mooseman
Moderator
Maybe a compression test will eliminate anything mechanically wrong with it. Then, check fuel pressure before looking at the injector.
Was planning on doing a compression test this weekend but on Thursday morning headed into work the CEL was on but when I left that afternoon it was off and hasn't returned since. Hopefully it was just a hiccup, but I'll keep an eye on it and thanks for all of the helpful info.
Finally got around to doing a compression test. All cylinders were between 130 and 150 except for number 4. It was at like 10 or 15 for the dry test and hit 70 - 75 on the wet test. This is pointing me to the piston rings, correct? Other than a rebuild, anything I can do to get compression up high enough to fix the misfire and pass inspection in a couple months? Been looking at Restore. Anybody ever use it?
Mooseman
Moderator
This is definitely pointing to a mechanical issue with the engine. Just to be thorough, you could do a leakdown test to definitely say it's the rings in that cylinder but in any case, it's rebuild or replacement time. Loss of compression can't be fixed by a band-aid solution and this is a big loss.
And Restore has been proven to screw up our VVT system.
And Restore has been proven to screw up our VVT system.