Cylinder 1 misfire

capncc

New member
2011 Rubicon
2.5 inch lift
35x12.50 NITTO ridge grapplers
5:13 gears
97500 miles
Superchips 91 octane tune

I was accelerating rating up the local toll road hill and she started shutting down , engine light comes on. Nurse it on home and DTC is PO301- cylinder 1 misfire. Replaced plugs, wires and coil pack cleared he code and test drove no problems. Drove to to next day it’s ok, heading home got on the same toll road accelerating up the hill she shuts down again same code and now it’s knocking and misfiring all the time. Time to get a compression check. Anyone have this problem?
 
Injector issue?

Do a compression and a leakdown test, but if you replaced all the ignition parts, I'd look at injectors next.

Also, possibly look at the ignition wiring, trace it back along with the injector wiring. Look for damage.
 

Noble Woodsman

New member
I haven't had this issue with a jk yet, but there are a few things you can try if the compression looks okay...

Check vacuum pressure

Check fuel pressure

Swap the new coil, spark plug, and spark plug wire with another cylinder, reset codes and check if misfire moves to the new cylinder

Swap fuel injector with another cylinder and see if misfire moves

Replace Camshaft position sensor. I would try this last, because it's less likely and it's more of a part swapping approach instead of troubleshooting.

It may be a good idea to return the programming to stock first. I'm not sure if the 91 octane program would complicate the search.


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cozdude

Guy with a Red 2-Door
2011 Rubicon
2.5 inch lift
35x12.50 NITTO ridge grapplers
5:13 gears
97500 miles
Superchips 91 octane tune

I was accelerating rating up the local toll road hill and she started shutting down , engine light comes on. Nurse it on home and DTC is PO301- cylinder 1 misfire. Replaced plugs, wires and coil pack cleared he code and test drove no problems. Drove to to next day it’s ok, heading home got on the same toll road accelerating up the hill she shuts down again same code and now it’s knocking and misfiring all the time. Time to get a compression check. Anyone have this problem?

Easiest thing to do would be to move the plug and wire to 2 different cylinders. If the misfire follows either one of those then that’s your issue. If it stays at cyl 1 then it’s going to be an injector issue.

Do you have any other codes popping up as well?
 

capncc

New member
Compression test results

I did the compression test and here it is:
Cylinders 1,3,4,5 and 6 are 185 psi
Cylinder 2 was 30 psi and the plug electrode-had oil on it
I’m not sure why the code was PO301
 

Noble Woodsman

New member
I did the compression test and here it is:
Cylinders 1,3,4,5 and 6 are 185 psi
Cylinder 2 was 30 psi and the plug electrode-had oil on it
I’m not sure why the code was PO301

Wow. Any idea why compression is bad on cylinder 2 only?


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30 psi isn’t really enough to run. You sure you got a good seal on the hose?
If it’s actually at 30 you should’ve had a hell of a lot more codes.


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