Hi Folks,

Looking for your expertise.

The problem: Random Misfires on cylinders 1,3,5 - Confirmed with Scanner
The Jeep: 2012 JKU 6-Speed, 108K miles
How long: I've been trying to fix this: 9 months

It's hard to feel the misfire when under throttle, but you can hear and feel the slight misfire trembles when at idle.

What I've tried so far:
- New Spark Plugs: (2 set's - 6 NKG & 6 Champion) Properly Gapped
- New Coils: MSD
- New O2 Sensors (all 4 - both sides)
- New Crankshaft Position Sensor
- New MAP Sensor
- All new Rocker Arms and Lifters on that bank (Cyl 1,3,5)
- New Camshaft Position Sensor
- New Injector on Cyl 5 = No change still misfiring
- New upper and lower o-rings for injectors
- New upper and lower o-rings for Lower and Upper Manifolds

Tests Completed:
- Leakdown Test Showed Normal
- Rotated Coils - No Change
- Rotated Plugs - No Change
- Camshafts inspection - no flat spots found

Additional Modifications Possibly Affecting Performance:
Mishimoto Oil Catch Can
Banks CAI
Odyssey Battery

Additional Fixes Completed on Motor:
- New Oil Pressure Sensor


Friends,
Please help. I love my jeep, and I want to drive it to 300k miles and drop in a Hemi and keep driving it.

(Wave),
Matt

 

Matt, check your profile, visitor messages..

 

HEY, I WAS JUST WONDERING IF YOU GOT YOUR MISFIRE ISSUE RESOLVED? I RUN A SHOP AND WE HAVE A 2012 JK WITH SAME ISSUES AND WEVE REPLACED EVERYTHING YOU HAVE AND WERE STUMPED. ANY INFO WOULD BE APPRECIATED. THANK YOU

 

I've got a similar problem, although mine had been cylinder 4 misfire, PO304. Good compression to cylinder 4. I replaced the 6 spark plugs with Champion (Mopar), the 6 coils with Mopar, and all 6 fuel injectors. I cleaned the Mass Air Flow (MAF) sensor in the air intake and replaced the Mass Air Pressure (MAP) sensor near the throttle body. Still no luck, kept getting P0304. Then I just recently replaced the lower intake manifold and replaced all 12 rubber gaskets, 6 on the bottom and 6 on the top and correctly torqued all bolts as I had found 2 of the long bolts going from the upper intake manifold to the bottom couldn't be correctly torqued (they were stripped into the plastic lower manifold). Interesting now that my check engine light code has switched to P0300, random/multiple cylinder misfire. The car feels like it drives fine and idles nicely. Thoughts on why the code has changed? Maybe one of the lower gaskets twisted or something during the lower intake manifold install?? Hate tearing it apart again, however now that the code has changed I'm thinking I'm making progress? Next step might be to perform a smoke test to see if I have a vacuum leak somewhere?? Help please!!

 

First, your profile shows a '20 model, or a JL. I presume you still have the 3.6L engine in it so lot could still be relevant. take a look at this thread cuz seeing the valves on cylinder 4 on this engine were surprising -

https://www.jk-forum.com/forums/stoc...ooting-360742/

 

Thanks, fixed my model year to 2016 JK. Read the post in the link lots of things to consider, almost all of it over my head so the next stop is likely my mechanic. The one thing I noticed that bothered me was when installing the new lower intake manifold it didn't seem to sit flush, it moved about a bit, all the bolts lined up and were easily torqued but now I'm wondering if a piece of debris got between the manifold and the mounting area or one or more of the gaskets fell out during the install. Thanks!

 

it is really hard due to lack of space to get anything down under that upper intake, but you might try to see if you can get any starter fluid down in that area with the engine running. If one of those gaskets was compromised, the intake should suck that starter fluid right in and you'd hear the engine rev up. but, it would be pretty tough. sitting at work, i can't envision if there is enough room to get a straw past the oil filter housing or not to reach down in there. Maybe a "custom" small hose hooked to straw on the can?? idk, the thought of removing all that to inspect hurts my head. I've been in my engine enough times to feel that pain.

 

Thanks, I removed the lower manifold once again and did find a piece of debris, removed it, cleaned the mating surface super good, checked the lower and upper gaskets as all were new, they looked really good. Put it back together and properly torqued all bolts. Cleared the code and drove it for about 100 miles over 5 days and the damn code came back. P0300. I notice when I first start it up and it's revving a bit higher there is a slight miss but as soon as the rpms drop down to idle it's nice and smooth and the Jeep drives fine. I'm also getting what I think is good gas mileage at 19.5 (which nice wheels and 33" tires). I have since replaced both cam positioning sensors. The passenger side looked terrible, all full of oily gunk whereas the driver's side looked super clean. I also replaced the vapor canister purge valve. Drove it for a while and the code P0300 came back again. The only thing I haven't replaced yet are the valve cover gaskets and the PCV valve (which looks brutal to replace). Any further suggestions? Thanks, Rich