P0306 Misfire Help

Artisanau

New Member
Joined
Sep 15, 2020
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2
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Australia
Hi Forum Members.

Just got home from a trip to the stealership with my 2013 JK throwing out the P0306 code randomly. Can go for weeks or days before replicating with the EML light coming on?

Out of further frustration of the dealer telling me what I already knew for $150, I decided to continue the hunt online with a hot coffee. First post I came to was one from M Duncan 'Matt'.

A thorough explanation and almost similar to mine. Firstly I wondered if he'd resolved his issue as I can't seem to send a reply to his thread? It's probably me, I'm not used to going on these kinds of forums to engage so it's all new, apologies to those who are tech savvy😂 Anyway back on track, I got fed up trying to trace a likely wiring fault with no clue as to what wires were going where with a multimeter, although I did separate clean and check I think, all of the multi connectors. The engine has only done 75'000Km which is nothing. I replaced the plugs due to 4 having a higher resistance than the specs suggest despite the low Kms and changed out the coil but no change as with Matt's JK. I take it to the dealer and end up with them tellIng me what I told them. I think they just put it onto the code reader and didn't look beyond that. I tried talking to the desk supervisor but they don't seem to have the old fashioned people skills they one did. They get easily offended if you try to discuss logic and your car with them.

I assumed when I took it in, it would be put on a tuner where they'd actually look at an oscilloscope etc to determine wether or not it was actually misfiring which it doesn't seem to be, it purrs as it's always done. They want $500 to do a bypass test and compression but I think if I had an issue with the mechanical side you'd know about it, ie, the left cyl head issues re' Mexico builds etc and the fact it's intermittent too makes me think wiring or maybe PCM?

The PCM On occasion seems to get very hot behind the screenwash bottle with the heat coming up from the exh manifold and I'm wondering if maybe that's effecting the coil switches or switch for cyl 6 inside especially at idle in traffic with limited air flow through the engine etc. Any help or suggestions likewise I'll investigate. Apologies for the long winded explanation, next time I'll try and abbreviate as best possible. Like Matt, I feel the same about owning my JK, I won't part with it and want to persist in finding the fault but without the help of the dealership. I'm going in! 👊

Thanks Mark.
 

cpwolf

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Aug 17, 2020
Messages
72
Location
Cedar Park, TX
If I’m not mistake , P0306 means specifically a misfire in 6.
Main causes from easy to find to harder Plugs-Plug Wires-Coil Pack.

Then I’d look at a fuel injector on 6 (It runs well, there are ways to clean, maybe it’s that)
This is a generic “chase down vacuum leaks article I’ve used.
then a vacuum (which actually Is a place I’d look).

Last is crank shaft position sensors. They can go and read wrong and start causing issues.
Unfortunately this isn’t a here’s the symptom, here’s the issue.

You’re gonna have to “go on a walkabout” in the Jeep to find it - see how I my the Croc Dundee reference there? Ha

Good luck and let us know, I know the frustrations, wish I was able to pinpoint More.
 
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Artisanau

New Member
Joined
Sep 15, 2020
Messages
2
Location
Australia
😂 thanks for your input 'cpwolf'. Yeah it's bit of a mine field. I thought if it was the crank sensors a code would of been picked up by the dealer earlier today but I can't rely on them. I'll get stuck in over the weekend and see if I've over looked something and I'll double check for vac leaks but like I say it runs as smooth as silk so it's a mystery but I'll re post if I cure it. 👍
 

BLACKJKU

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Feb 22, 2020
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Huntington In
If you do replace parts don't go cheap because they probably will still throw codes. Buy OEM and you won't have problems.