"Dreaded" P0304 *HELP* - JeepForum.com
 
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post #1 of 9 Old 09-10-2019, 06:15 AM Thread Starter
Shane361
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"Dreaded" P0304 *HELP*

So my wife has a damn near mint 2016 Jeep Wrangler, no mods, babied and 36,880 miles. The only thing I have done to it is change the battery out last week due to a dead cell.

Yesterday she tells me her check engine light came on and when I checked the code it was a P0304 or misfire in Cylinder 4. Now it's my understanding this could be an air leak, bad coil pack, spark plug, head, bad fuel, gas cap lose or pretty much anything that has to do with the combustion chamber on cylinder 4. When I did my engine visual I noticed her coolant level in the overflow tank was at the very bottom, not good. Now I have thoughts of a blown head gasket. The level in the radiator was fine, not milky. Other than checking the gas cap, airbox for leaks I swapped #4 and #6 coil pack to see if I got a swap in code to P0306. I had also disconnected the batter before doing so. Reconnected the battery and started the vehicle up, seemed normal as before. Drove 5 miles and to be seemed normal with a small notice of shake around 1K. The check engine light never came on nor did any code when I ran them, just "Done" which means no codes on the self diagnostic test the Jeep has. I would have pulled plugs for a visual but from a video I watched this guy took half the engine apart to get to them, not ready to do that just yet. I told her to drive it normally tomorrow and look for any difference is sound, vibration or power. If the light comes on let me know asap. I will also contact the dealership but as we are JUST out of our warranty(of course) not sure what they will do.
Thanks for any help which is greatly appreciated. She likes her Jeeps...3rd or 4th one in a row. -Shane

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post #2 of 9 Old 09-10-2019, 07:17 AM
jtec
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Ok you swapped coils, and are waiting - fingers crossed- the CEL remains off. Sounds like a reasonable plan.
Yeah hear that often - I have to remove WHAT to replace plugs - often a few choice words are added...

Add 1 can of 'seafoam' a fuel system cleaner. As good a time as any.
Do not erase codes or remove battery as you dump information that the computer stores, some will be usefull in diagnostics.

FYI with increased use mode $0A $10 they (codes) are 'pertinently' stored only techs with jedi powers can see them, ok maybe a good scanner is also needed. BIg brother .

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 9 Old 09-10-2019, 07:24 AM
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wanted to add - might want to review attachment with your friendly local jeep dealer...

As for adding a little coolant- keep you eye on it - I doubt you paid attention before this issue... think positive
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File Type: pdf p0305.pdf (30.9 KB, 6 views)

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #4 of 9 Old 09-10-2019, 07:48 AM Thread Starter
Shane361
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Quote:
Originally Posted by jtec View Post
wanted to add - might want to review attachment with your friendly local jeep dealer...

As for adding a little coolant- keep you eye on it - I doubt you paid attention before this issue... think positive
Thank You Very Much, I will get ahold of dealer with this.
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post #5 of 9 Old 09-10-2019, 08:22 AM
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OOPs I think my fat finger typing may have entered wrong numbers, your issue is #4 - I think TSB was for #5 ....sorry if I caused confusion.

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 9 Old 09-10-2019, 01:38 PM Thread Starter
Shane361
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Originally Posted by jtec View Post
OOPs I think my fat finger typing may have entered wrong numbers, your issue is #4 - I think TSB was for #5 ....sorry if I caused confusion.
No worries. Code still has not come back. I did order a leak test kit to see if its the head.

The Jeep should still be under the valve train warranty and if any issues come back it's going in.
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post #7 of 9 Old 09-16-2019, 07:38 PM Thread Starter
Shane361
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Update...
So the Code P0304 did indeed come back even after swapping Coils. So the coil is good, I pulled the spark plug and will post that picture. Not 100% sure what they should look like good and bad so any insight there is appreciated. I noticed when pulling the plug the two silver tubing going down the passenger side just above the plugs were very hot, especially for being parked for two hours with the hood up. I wouldn't think anything would be able to burn you after two hours. Also tonight I did throw some Lucas in the tank with some Premium just in case it was bad gas from that gas station she had never been to before. Thoughts on the plug? -Shane
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post #8 of 9 Old 09-16-2019, 08:05 PM Thread Starter
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Bought some new plugs, the old plug looks bent up and more of a gap than a new one. Not sure it's sufficient enough of a difference but we shall see. Bought 6 and I'll get around to changing them all out. Who ever designed this engine hated you guys.....lol.
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post #9 of 9 Old 09-19-2019, 02:47 PM Thread Starter
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Leak Tester came in and I tested the vehicle for a blown head gasket which it did not have luckily. Currently going with bad gas but it has only been a few days since we treated the tank and cleared the code. I'm optimistic.
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