Lookin for some input from the gurus!
06 jeep tj sport 4.0 auto, 23k original miles - Inherited 2 years ago and have been tracking a P0300 random misfire from day 1. Only happens on cold start/first start of the day, runs great otherwise (although power seems like it should be better, not my first TJ).
Have been reading every forum possible and trying everything I know, but nothing changes. Jeep is currently at it's second mechanic shop, so I'm turning to my experienced Jeeper pals here for any recommended approaches.... here we go...
What's been done so far:
Spark plugs- 3 different types (per forums, aware of temperamental issues when trying to get fancy here - current NTK's gapped to .035, plugs not the issue.)
Crankshaft sensor
Opda - kept original CPS sensor
All new 02's
Fuel system flush (first mechanic)
Fuel stabilizers through tank twice (was a lake jeep, so just in case)
Current mechanic notes:
I looked at historical misfires and cylinders 1,4,5,6 all had misfires, I monitored misfires while idling and only cylinder 4 had minor misfires, I used coil tester while idling and all coils we’re lighting tester. I pulled ignition coil off and inspected coil boots no issues found, I removed spark plugs and inspected them no issues were found, I performed compression test and found cylinder 3 to have higher compression than the rest and cylinder 6 to have lower compression than the rest.
Cylinder 1 compression; 136
Cylinder 2 compression; 136
Cylinder 3 compression; 145
Cylinder 4 compression; 136
Cylinder 5 compression; 131
Cylinder 6 compression; 109
Lower compression on cylinder six is concerning but is not enough to confirm this is the issue causing misfire. At this time I would like more diagnostic time to continue diagnosis and monitor fuel trims and test for vacuum leaks and watch for rich or lean conditions, I would like to lab scope main sensors, like cam, crank, map sensors.
Why I'm here:
Before I give the green light to triple my bill for the above-mentioned continued diagnostics, curious if anyone has experience with this issue or suggested areas to start additional diagnostics? I've had suspicions with the Catalytic converters (bluedriver readings on bank 2 down 2 02), but temp tests proved Pre cats fine and rear cat mayyyybe suspect. Also, the jeeps use was strictly at a lake to drop in Water-toys for a decade, so carbon buildup/stuck valve, maybe?...
Thanks for any suggestions/direction, all! Questions welcome also, would love to have a confident plan of attack for Monday morning to try to fix this once and for all.
06 jeep tj sport 4.0 auto, 23k original miles - Inherited 2 years ago and have been tracking a P0300 random misfire from day 1. Only happens on cold start/first start of the day, runs great otherwise (although power seems like it should be better, not my first TJ).
Have been reading every forum possible and trying everything I know, but nothing changes. Jeep is currently at it's second mechanic shop, so I'm turning to my experienced Jeeper pals here for any recommended approaches.... here we go...
What's been done so far:
Spark plugs- 3 different types (per forums, aware of temperamental issues when trying to get fancy here - current NTK's gapped to .035, plugs not the issue.)
Crankshaft sensor
Opda - kept original CPS sensor
All new 02's
Fuel system flush (first mechanic)
Fuel stabilizers through tank twice (was a lake jeep, so just in case)
Current mechanic notes:
I looked at historical misfires and cylinders 1,4,5,6 all had misfires, I monitored misfires while idling and only cylinder 4 had minor misfires, I used coil tester while idling and all coils we’re lighting tester. I pulled ignition coil off and inspected coil boots no issues found, I removed spark plugs and inspected them no issues were found, I performed compression test and found cylinder 3 to have higher compression than the rest and cylinder 6 to have lower compression than the rest.
Cylinder 1 compression; 136
Cylinder 2 compression; 136
Cylinder 3 compression; 145
Cylinder 4 compression; 136
Cylinder 5 compression; 131
Cylinder 6 compression; 109
Lower compression on cylinder six is concerning but is not enough to confirm this is the issue causing misfire. At this time I would like more diagnostic time to continue diagnosis and monitor fuel trims and test for vacuum leaks and watch for rich or lean conditions, I would like to lab scope main sensors, like cam, crank, map sensors.
Why I'm here:
Before I give the green light to triple my bill for the above-mentioned continued diagnostics, curious if anyone has experience with this issue or suggested areas to start additional diagnostics? I've had suspicions with the Catalytic converters (bluedriver readings on bank 2 down 2 02), but temp tests proved Pre cats fine and rear cat mayyyybe suspect. Also, the jeeps use was strictly at a lake to drop in Water-toys for a decade, so carbon buildup/stuck valve, maybe?...
Thanks for any suggestions/direction, all! Questions welcome also, would love to have a confident plan of attack for Monday morning to try to fix this once and for all.
