Cylinder misfiring and ghost P0303 code
- Thread starter 0121whit
- Start date
OP
Ntk’s and walkers. I think. I work at O’reillys so I get what I can find. I know for a fact they aren’t bosch
Have you gone through your wiring loom back to the PCM? TJs are notorious for chaffed and broken wires at the back on the engine where the loom turns.
-Mac
-Mac
OP
Yes have been through it multiple times, also wrapped it in an old shop rag a few times and zip tied it off the valve cover so it doesn’t rub
Do you by any chance have to run a higher octane gasoline than 87 to prevent it from pinging, if it ever pinged?
OP
I’ve tried 87, 90, and 93 octane all three throw the code. I’ve even tried non ethanol
OP
Grasping at straws again with that last question. Was hoping perhaps the engine was just carboned up which could cause a misfire. Excessive carbon-buildup, which is easy to get rid of, can cause the engine to ping on 87 octane.
Can you feel the misfire? Did you clear the code after putting in these new parts? And finally, when you removed the number three plug, did it look any different than the others?
OP
Plug looked slightly more fouled due to misfire and yes I can feel the misfire. I have cleared the code and all after every part change. I’m literally pulling the invisible hair out of my bald head trying to figure this out.
OP
new symptom @Jerry Bransford
Flashing CEL on random cold starts. I can clear it, and the jeep runs totally normal. Wait for about 5 minutes then all of a sudden misfiring again. I’m thinking since we are all grasping at straws, replace the ECM?
Flashing CEL on random cold starts. I can clear it, and the jeep runs totally normal. Wait for about 5 minutes then all of a sudden misfiring again. I’m thinking since we are all grasping at straws, replace the ECM?
OP
If unfixable where is the best place to get a remanned or new?
Same spot. Mark is the best. I'd rather have someone tell me a part is just fine rather than just shipping a replacement.
-Mac
@0121whit You can call me anytime to discuss your pcm issues. All testing and repair cost go towards replacement if yours is not repairable.
Thanks,
Mark
Thanks,
Mark
The random misfires problem occurred on my '01 4.0L for quite some time and no matter what I did; the problem persisted....
Several months ago I needed to replace a badly worn clutch throw out bearing.
At the same time I replaced the clutch, pressure plate, flywheel and cleaned the transmission shaft.
While replacing the flywheel I noticed the CPS triggering blocks had a lot of surface rust and the CPS had rusty dust on the pickup surface.
I wiped off the rusty dust from the CPS and the new flywheel CPS triggering blocks were rust free.
Since that time the random misfires have disappeared other than a brief period when I found the #1 spark plug misfiring which I cured by replacing the spark plug.
Remove the CPS and inspect the CPS pick up surface for rusty dust or metallic dust and try to inspect the flywheel triggering blocks for rust thru the CPS mounting hole (difficult to see, but it can be done).
Several months ago I needed to replace a badly worn clutch throw out bearing.
At the same time I replaced the clutch, pressure plate, flywheel and cleaned the transmission shaft.
While replacing the flywheel I noticed the CPS triggering blocks had a lot of surface rust and the CPS had rusty dust on the pickup surface.
I wiped off the rusty dust from the CPS and the new flywheel CPS triggering blocks were rust free.
Since that time the random misfires have disappeared other than a brief period when I found the #1 spark plug misfiring which I cured by replacing the spark plug.
Remove the CPS and inspect the CPS pick up surface for rusty dust or metallic dust and try to inspect the flywheel triggering blocks for rust thru the CPS mounting hole (difficult to see, but it can be done).