I've read all 49 threads that pop up when searching for p0306 in the tj section. I have a 2001 4.0 manual with about 225000 miles. I bought the jeep with about 220000 about 2 years ago. It was a very clean 1 owner jeep for the miles but had some cylinder misfires when I bought it. Come to find out it had a leaking valve and cracked head. I put a rebuilt head on and the problem went away for a while. Now I have a cylinder 6 misfire popping up. It seems to run okay for a while, then my CEL starts flashing for a minute then just stays on. I've cleared codes several times, but it keeps coming back.
Things I've done and changed
-Completely Cleaned Intake
-Replaced IAC
-Replaced TPS
-Replaced Coil Pack
-Replaced Spark plugs with Champion 985's gapped at .035
-Checked electrical plugs and connections
-Swapped spark plugs between cylinder 6 and 1 to verify I didn't have a bad one
-Swapped injectors between cylinder 6 and 1 to eliminate a bad injector, changed the orings when I put the new head on
-Had a smoke test done recently for an evap leak, fixed the vacuum leak
-Tested fuel pressure and check valve, it checked out good
That's all I can think of for now. Do you think a bad O2 sensor or CKP could cause a misfire? I'm open to suggestions. Thank you for reading and for all the other good info I've picked up from this forum.
Things I've done and changed
-Completely Cleaned Intake
-Replaced IAC
-Replaced TPS
-Replaced Coil Pack
-Replaced Spark plugs with Champion 985's gapped at .035
-Checked electrical plugs and connections
-Swapped spark plugs between cylinder 6 and 1 to verify I didn't have a bad one
-Swapped injectors between cylinder 6 and 1 to eliminate a bad injector, changed the orings when I put the new head on
-Had a smoke test done recently for an evap leak, fixed the vacuum leak
-Tested fuel pressure and check valve, it checked out good
That's all I can think of for now. Do you think a bad O2 sensor or CKP could cause a misfire? I'm open to suggestions. Thank you for reading and for all the other good info I've picked up from this forum.