Do you have a 12 or 13 by chance? If so you may want to check with your dealer to see if it may be related to the cylinder head issue, if it is it may be covered by the extended cyl head warranty.

 

That is a cylinder 4 misfire code.

There is no reason to replace anything at this point since you will likely just be throwing parts at random without fixing the problem. You can however pull the plugs and inspect them to verify that the #4 cylinder is not firing correctly. Remember these engines have 100k mile plugs in them and it is not common for them to fail this early.

There are may things that can cause a misfire code including a plug, plug wire, coil pack, fuel and air mixture. A visual inspection should be done first to make sure nothing is unplugged. Next would be to use a quality scan tool to pull all codes. Something else that should be done is to graph the spark pattern on each of the plugs near and including #4 to verify exactly what is going on and narrow down your search for the problem. Once you know exactly what the problem is, then you can start testing components and replace what is actually wrong.

 

Got it. Will pull the plug this weekend and take a look. Our Sahara is 2014, so should be outside the range of the head issues.

 

I have a P 0303 misfire here in my 2016. Rubicon. Difference is mine is a little rough at idle. I replaced spark plug and coil and it did not fix it. Next stop is the dealer


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Getting back around to fixing this issue - Almost no discernable misfire felt in normal driving. Wife reported maybe once off the line she felt something, but wasn't sure.

I'm reading limited reports that some 2014-2015 are getting replacement heads with the same problem that was apparently fixed in the 2013/2014's.

Is there some way I can check if I have a bad head myself before throwing it at the dealer and it not be a warrantied-covered item?

 

My 14 through the 304 code at 36k miles and it ended up being the head. Took it to the dealership and they replaced it under the extended warranty for the issue.

 

Thanks. I reset the CEL again and will see how long it takes to come back on. I’d think if it was the head it should come on quickly. Once it does I’ll probably take it to the dealer since any diagnosis would require me to remove the intake manifold to gain access...and my research shows only a leak down test will confirm if the head is bad. I’ll report back once I figure out what it is.

 

CEL back on within 50 miles. No driving issues. Pretty confident it’s probably the head as a bad plug or coil pack would have a noticeable misfire...so going to drop her off this weekend at the dealer

Will report back. Hopefully I can get details on what failed.

 

I'm not sold on it being a head/ head gasket issue...
Have you tried to swap out the #4 spark plug with a plug from another cylinder to see if the misfire chases the plug? Just taking it out and looking at it won't tell you much. Unless it is covered in baked-on coolant or oil. You can compare it to other cylinders, but again, I doubt you will find anything conclusive.
Try swapping out the coil pack with another cylinder to see if it chases that.
Another thing you can try is to spray down the coil packs with a light mist of salt/water from a spray bottle. Salt water is more conductive than just water and can find voltage leaks better. Could be a coil housing, could be the wiring.
Make sure to hose all of it off with clean water when you are done.
Injector could be intermittently leaning out that cylinder. You can move those around too.
Watch the fuel trim numbers or each bank's O2 sensor value to see if the misfire is a lean misfire, or a rich mixture misfire from a leaking cylinder head/ gasket. Cracked or warped cylinder heads don't suck air in, but pull in coolant or oil and kill the flame, causing a misfire.
A bad crank sensor will also cause a false misfire reading, but usually its not that dead consistent with only one cylinder...
The next step would be to leak down check that cylinder, cold and hot.

If you could capture data from the misfire, that would help. Check to see if timing is being pulled from the knock sensor, or any big swings in a/f ratio, are there other cylinders with misfires, but didn't trip the CEL, etc.

I would imagine that these are the steps that a dealer tech would take before they would move forward on a cylinder head fix. On the other hand, the dealer would charge you to have their guy do these tests all over again anyway.....
Good luck and keep us posted.

 

Dropped car off and got the call today - head bad as I suspected. So I can confirm this issue includes 2014’s as well. Hopefully just a minority after 13...

They are telling me the opposite head is gunked up and Could do with cleaning. I’m very suspect because I’ve done perfect 0-20w Mobil1 Synthetic oil with factory filter every 8k. I think this is a money ploy to “flush” the engine. Maybe I’ll ask for a photo of the gunked up head because that’s very concerning.

Also said needs new thermostat...no CEL for this, nor is running temp off. So unsure about that one as well

 

Well quick turnaround, dealer got the left head replaced today.

Work report says Cylinder 2 had 40% leakdown result. My code was for Cylinder 4, so I assume the head had issues on multiple cylinders.

Problem solved!

 

Had the CEL come on my 2016 Rubicon at 36,400 miles. Just heard back from the dealer that they are replacing the cylinder head. Maybe they limited the issue after 2013, but it still happens it seems.

 

My CEL came on yesterday. 2016 JKU. my scanner said cylinder 4 misfire detected. I checked youtube on how to replace plugs and coil. OMFG. who made these engines? All the crap that has to be removed just to replace a plug is ridiculous. I have a dealer appt next week. I don't want to do all that work just to find out that I didn't fix the problem.

 

So, I had AAA flatbed my Jeep to the dealer. Three days later I get my Jeep back after paying the $1,100 ransom. They replaced cylinder 4 fuel injector and added some BG fuel induction (?) cleaner. It runs good as new. That's a lot of money, but if it's fixed for good then I'm ok with it. Had I tried to do this myself, I bet I would have replaced the plug and the coil on cylinder 4 and been done with it only to do it all over when it still misfired. That's a lot of work to do twice.

 

Just had this happen with my 16 JKU.
75k miles. Dealer is saying cylinder #4 needs to be rebuilt as the misfire is due to loss of compression. Car was a daily driver and never been off-road or driven hard. Anyone here know if Jeep is extending the coverage on this issue for newer model years? Dealer is quoting me $3500 for the repairs. Other mechanics i have spoken with recommend rebuilding the entire engine as they say it's only a matter of time before the other cylinders go too.

 

Just had this happen with my 16 JKU. 75k miles. Dealer is saying cylinder #4 needs to be rebuilt as the misfire is due to loss of compression. Car was a daily driver and never been off-road or driven hard. Anyone here know if Jeep is extending the coverage on this issue for newer model years? Dealer is quoting me $3500 for the repairs. Other mechanics i have spoken with recommend rebuilding the entire engine as they say it's only a matter of time before the other cylinders go too.

My 2016 is doing the same thing…P0302 code first which is the #2 cylinder misfire. Ended up replacing the head ($2900). Check engine light came on and it is now showing ode P0304 which is #4. They can’t find anything wrong…I’m at a loss of words and funds. Let me know how your issue turned out.

 

Welcome to the Forum, from Cave Creek AZ. Other than the 2012, and early built 2013’s, there is no extended warranty on the left cylinder head. As far as the new JL’s, the power train warranty is 6 years, or 60,000 miles whichever come first. Mopar does sell extended coverage, at the customer cost.

 

Been getting an intermittent 0304 code for a couple of weeks on my 2012. Jeep dealership won't test for head issue unless they go through entire trouble shooting tree (at my expense). I am going to go ahead and change spark plug and coils so I can rule that out, anything else I need to change in regards to this code?

Do I need an ignition capacitor / is it a good idea to change it out? Any wires to change out?

Thanks.

 

This p0304 was a head issue. Replaced under warranty.

 

Hey man. Saw you have a 12 with the same issue as me. I just bought a 2012 one owner with only 46k miles for my daughter. Drove it 12 hours home from Dallas to Florida with no issues. Next day I get engine light for same code while setting at stop light. No drivability issues at all. Reset it twice and it keeps coming back. How many miles/years does this extended warranty cover?

 

10 years, 150k miles. You will be right on the edge depending on your in-service date. You should contact a dealer and have them check your vin.

 

Thank you sir. Went to the dealer today to confirm. 1st owner bought it in April 2012. Just a few months left on warranty!

 

Depending on dealership they may want to change spark plugs, ignition coils, fuel injectors first. If you know when those may have been changed that might help speed up the troubleshooting. Supposedly once they start the process, you will still be under warranty even as they troubleshoot.

 

None of those have been done, only had 45,752 when I bought it

 

Jeeps, Same here! but at 142k in NZ. Mine's a 3.8, 2011. Just wondering: Is the left head issue a 3.7 one only? I'll be swapping, then replacing the plugs, then leads, then coil pack as first steps, and check back here for advice beyond that and will also post findings.
Cheers.

 

Head issue and extended warranty is 3.6l for 2012 and some early 2013.

 

If they do find out it is the head, While they are in there I would have them change out spark plugs and ignition coils at least on the drivers side. Passenger side is easy.

 

Here is the TSB

 

Th

Thanks heaps for the TSB doc. Mine's a 3.8 so I'll do the process of ignition component swap/fault elimination/ relocation & report back for advise. I'll grab a compression tester too.

I really hope I haven't blow a head gasket or warped a head.......fingers crossed.🙂

 

Hi. Have a 2016 Wrangler that has the Jeep Cylinder Head issue. Does anyone know whether Jeep extended the warranty on the 2016?? Pls let me know if you have any info on this. Thanks

 

No, the TSB above only applies to 2012 and some 2013s.

 

I have a 16 Jeep wrangler JK that's had the cylinder 4 misfire(1). Had dealership change the heads once under warrenty.. then 1 year later got the code again. Paid out of pocket 6k to replace heads(2) out of warrenty. MIsfire came back so they changed the v same parts 3x. Now we're fighting for them to fix it since they're saying we need a whole new engine bc it's cracked. Changed the same parts 4x should've shown that it was a problem enought...The problem with them fixing it is bc no one else is bringing in their jeeps to show it's a known or reoccurring issue.