P0306 Code and P0456

aidanm

TJ Enthusiast
Joined
Jan 18, 2023
Messages
200
Location
Virginia
Hi all,
So I’ve been having this p0306 code for several months and it’s driving me crazy because I can’t find the solution to it, I’ve tried basically everything I can think of to fix this misfire code. I’ve changed the rail, I’ve changed the spark plugs and changed the #6 plug again to make sure that one wasn’t bad, swapped #5 and #6 injectors to see if the problem followed and it didn’t, sprayed around with brake cleaner trying to find a vacuum leak, did a compression test, did a fuel pressure test, all looked good. I just checked my 2 smaller cats and there’s about a 60 degree difference between inlet and outlet of one and about an 80 degree difference in the other. Every time I scan the code is says it’s right around 700 rpm that the misfire happens. Also I can feel it when I’m idling - it’s kind of like it has a small cam but when I’m at higher rpm for a while it’s fine. Any ideas would be appreciated.
 
If it was completely failed sure. You'd also get no RPM at crank.

You're CPS is either dirty or old and intermittent. Or an off brand...we typically recommend Mopar, I used a Napa Echlin on my 97 and others report good luck with Standard Motor Products.

I chased random misfires on mine for months and replacing the CPS fixed it.

Or it's wiring and nothing is wrong with the CPS.

-Mac
 
If it was completely failed sure. You'd also get no RPM at crank.

You're CPS is either dirty or old and intermittent. Or an off brand...we typically recommend Mopar, I used a Napa Echlin on my 97 and others report good luck with Standard Motor Products.

I chased random misfires on mine for months and replacing the CPS fixed it.

Or it's wiring and nothing is wrong with the CPS.

-Mac

Okay thank you! It is the original CPS so I’m sure that may have something to do with it
 
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