Donni

I bought this Jeep new in January '15 with only 37 miles on it. Took it on a trip from Texas to California in June of the same year. Didn't have any issues with it until I got into New Mexico when the check engine light started blinking. Pulled over and checked things out and found no issues at all. Engine was running smooth and I was getting the expected gas mileage. The light went out and we headed out again. It later came back on and blinked for about 30 seconds and then went solid and stayed on. Found a Jeep dealer in Las Cruses and they ran the codes which read misfire. Since the engine was running smooth and there were no noticeable issues with it, they cleared it and I went on my way stating that it was probably just a fluke and if it persisted, take it to the dealer when I got home unless I experienced more serious symptoms. The code didn't show up again until I reached the AZ/CA state line. I took note of what the engine was doing and what I was asking it to do when it came on. This only happens when I'm traveling at 70 to 75 mph and reach a steep grade up while in cruise control. If steep enough, the Jeep will down shift and as the RPM rise to over 3000, the CEL will alarm and blink until I reach the top of the grade. If it's long enough and the Jeep has to downshift again, the light blinks again and then stays on permanently until the code is cleared. Again, no audible or visual symptoms seen and the gas mileage was still what is expected for the Jeep.

After returning home, the dealer flashed the ECM for a recall and said that everything checked out fine in early July. The CEL never flashed or came back on until mid February of this year and it happened in New Mexico entering into a steep grade where the Jeep was asked to down shift at 75 mph on cruise. It was the exact same issue that I experienced the year before. Again, there was no audible or visual symptoms and the Jeep was still getting the same gas mileage. After returning home I took it back into my dealer and informed them of the same issue. I also have done some exhaustive searching all through the internet looking for a similar issue and a possible cause. I've found many complaints of this very issue with just as many "causes" but often this issue keeps reoccurring. Yesterday, I get the Jeep back and this is what I was told: They replaced the intake gasket, Tappet-valve Lash, Arm-valve, then took it for a test drive where there wasn't a misfire with the tester still plugged in. When the tech came back to the garage, with the reader still plugged in and the engine in idle, it pinged 160 misfire codes on cylinder 6, just in idle. But you can't feel the misfire or hear it. They swapped the coils, plugs, roller rockers, and injectors on cylinder 6 and test drove without anymore codes.

When I got it back, I started having unrelated issues with the cooling and heating of the Jeep, of which, I know is not related to this problem but more likely related to a connector that was bumped or reconnected wrong when they were working on it. My point, I had to take it back and not able to go and recreate the steep grade scenario to see if it will throw another misfire code. Here's my issue with this, I have 2 '15 JK Ruby's that were bought on the same day. The one I'm having issues with is the Unlimited. I have a 2 dr soft top that hasn't been in the same conditions that I put the unlimited in and I'm afraid I might have the same issues with it. My intention is to get find a steep enough grade that I can get the Jeep up to 75 mph and ask it to downshift. When I do, I'll come back on here and post my results of the "test".

My question is, has anyone else experienced this same issue with the newer models? All of the posts that I've successfully found, are older models '12 and earlier and if so, was the issue resolved and how. With that being said, the service manager told me that this was a very unique issue and that the tech had to call Chrysler to help them trouble shoot the issue, and my problem with that is that this issue seems to be a bit more common than his "unique" tag placed on my current situation. He also said something that was rather disturbing and with my history with all cars and trucks, a misfire is something very obvious and is audible and can be seen visually with the vehicle tremor lightly but can also be pretty severe. He said that on these Jeeps, the computer compensates for this issue and that the misfire can't be seen or heard. This made absolutely no sense to me at all but seeing that my experience is with older model vehicles, I'm in no position to argue confidently.

Thanks for the time and help!


OK, I tried to recreate the problem in my '15 2 dr JK Ruby this afternoon and was not able to get the CEL to ping a misfire. Which, is good news. Another idea that I have, every time the CEL lit up the Jeep was above 1200 ft above sea level. I took the problem Jeep on the same route I took today, which should have caused the same misfire, last December and did not have the issue then. It's an interesting concept, but one worth investigating further.

Hopefully, there will be someone out there with similar issues and experiences, or has worked on one that knows the scenario that caused their issue.

sikm3

Did they tell you whether the spark plug in cylinder #6 was indicative of whether you were running lean or rich?

It look as if they replaced everything ignition related plus the fuel injector (the usual suspects in a misfire scenario). I would probably run fuel injector cleaner from your local auto store for a few fill-ups to ensure the fuel injectors are clean. If the CEL code returns, it could be due to other things:
Could also be a bad coolant sensor
Could also be an air leak which can occur in vacuum hose connections, the throttle body or intake manifold gaskets, or the PCV
Check the MAF sensor to ensure it's clean....clean it with electronics cleaner
Check fuel pressures to ensure you're not running lean
You may also want to get your compression reading to ensure you don't have a leak in the head gasket

There's really no magic bullet for finding misfires. It takes a certain amount of detective work to isolate the fault and determine the underlying cause. Good luck!!!

Donni

Well, supposedly they were on the phone with Chrysler doing the trouble shooting and they had them run through several senarios, pulling and moving coil wires and such. What baffles them, it's popping the misfire codes randomly. Sometimes, they're popped during the test drive and at other time, popping only when it's in idle. However, they did say that if it's not "fixed", the next step would probably be pulling the engine and replacing it. Just kind of scary knowing that a Jeep that was just months old when this all began and still not "fixed", could potentially have issues from now on. At least there are lemon laws, worst case of course. Hopefully, it'll all be taken care of and I won't have anymore issues but only time will tell. Thanks for your input, I'll be sure and add this to my list of questions, if forced to take them to the wall. Trying to stay positive here but when they really don't know the issue and are just replacing parts willy nilly, kind of makes a person twitch!

Donni

I forgot to mention this.... In all my own research into this, cylinder 6 seems to be one that is mentioned the most. They never mentioned the condition of the cylinder or the plug for that matter, nor is it mentioned in the notes on the service order. One can only assume, after Chrysler asked them to preform certain procedures, they just replaced what they were told to replace without noting the condition of the parts. After all, they don't have to live with the problem, just attempt to fix it as per Chrysler's instructions. Factory warranty can be a great thing but it can also be a nightmare, especially if they don't want to spend the money for the repairs.

Donni

I went to pick up the Jeep yesterday and asked to speak with the mechanic that was working on it. He's not a young man and has been a mechanic for nearly 30 years, working for Chrysler for about 20 of those years so, I knew that he had the knowledge and the training and if there was a "fix", he would be the one that could do it.

When I started asking the questions that I've been asking all along, he quickly realized he wasn't dealing with an idiot and was at ease as well. To make this short and sweet, the parts that he replaced as per Chrysler's request, was one of those "lets cover all our bases, just in case" scenarios. When he was told by Chrysler to replace the parts on the 6th cylinder, it didn't make sense to him, nor me for that matter, but he is required to replace those parts in an effort to please the customer. It was one of those things that if you show an effort, the customer feels more secure that they've bought a dependable vehicle. Well, that's all fine and good but a REAL Jeep owner knows what they are buying and getting, before walking into the dealer. The only thing we're concerned with at this point in the process is color and $$$.

So, the conclusion is exactly what I told the service rep, the issue with the Jeep isn't any mechanical issue, it's a software issue that is being dealt with and a firmware upgrade is in the works as we speak. All I have to do is call every now and then and inquire about it because it's not going to be a recall, as it doesn't pose any threat of damage on the vehicle. If the code is thrown, you take it in and they do the flash, if not....bully for you. For this code to be thrown, circumstances have to be right and one of those was exactly what I stated. You have to be traveling at around 70 to 75 mph, hit a steep uphill grade which, asks the computer to downshift to maintain that speed and as the RPMs rise to around 3000, the Jeep thinks it's reading a misfire even when there's not one present. He was impressed that I took the time to read a topo map to get the elevation when this happened. Every time the CEL was activated, I was at at least 1200 feet above sea level and that's why we don't see many of these issues here where I live. We don't have all the right conditions around here just in our everyday driving.

I hope this thread helps another Jeep owner that is having similar issues and wish I would have found information such as this, when I first had the problem. I sure would have slept easier! Oh, just in case anyone is wondering, the bull crap the service manager fed me about not being able to feel a "misfire" was complete rubish but then again, I already knew that. Just because I'm a woman doesn't mean I can't run circles around you under the hood of an automobile. One thing I do know, computer and the knowledge on exactly how and why an engine of any kind operates. Never judge a book by the cover, you'll get stung eventually.

mr72

I hope you are right, that it's just some kind of software issue. But I doubt it. Mostly because if it was software, all of them would do it, at least all of them with that rev of software. And not all 2015s do this.

If it was me I'd demand they do a compression test on that bank.

If it is misfiring due to ignition failure, then you risk fouling the catalytic converter by driving it while it is misfiring. If it is misfiring due to a poor fuel injector or an air leak somewhere (lean condition), you risk a burned valve by driving it while it's misfiring. Also if it's misfiring while running lean, you probably also have a risk if pinging and you might risk bending a valve or damaging a piston. You'd be able to tell by looking at the spark plug. If it was misfiring due to insufficient valve lash, then only the out-of-adjustment valve is at risk of being burned. It sounds like they suspected all of these things and preemptively fixed them. I'm not surprised, since misfire can be extremely difficult to diagnose.

Could be a dozen other things but most of them would cause a P0300 rather than or in addition to a P0306 so I would tend to rule them out.

Fortunately, if it's misfiring due to a cracked head, it basically won't risk anything else. Unfortunately, it's got a cracked head. And even though they hope the >2012 heads fix the problem, there's plenty of evidence out there that cracked heads exist even in 2015s, and the symptom is always a misfire that eventually becomes common and eventually also leads to an audible tapping sound. Your steep grade aggravation of the issue makes me think the cracked head is the more likely cause, because cylinder pressures are very high under those conditions (low rpm, high load, high throttle).

sikm3

I'm not so sure it's a software issue....hope it works out but I'd be testing that scenario again to see if the problem reoccurs.

Huss

My 2012 was doing that and it ended up being the dreaded replace left cylinder head ordeal. But that must have been sorted by now, right?

It was an ordeal as it required three visits to my dealership. To replace the head, then to bring it back to fix the oil leak they had created. Then to bring it back to fix the coolant leak they had created.
And since that fix it immediately had a harmonic buzzing vibration between the dash and the firewall. I'll never go back to that dealer again.