Random Cylinder Misfire

So my random cylinder 6 misfire has returned. Back in August 2016 had a problem with check engine light coming on due to high RPM in 3rd gear. Would push to 4000-4500 RPM and then the check engine light would flash multiple times then it would upshift. It only happens at times from acceleration up steep grades. At that time they re flashed the PCM and no issues. But I live in the flat land of the Midwest.

Now last week it has returned. Finally got a chance to get the JK back out to the hills. Spent a few days in the Black Hills, and every time we were on an uphill grade from a start, I had a choice push to 4000-4500 RPM and wait for the light to upshift or take the hill at 45 mph. Spoke to my dealership in Wisconsin today and obviously they have never heard of it, due to our lack of hills.

So my question, has anyone dealt with this in the past in mountainous areas? And if so what can I tell the dealership to do to fix it?


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Also it's a 2016 Rubicon


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Not that it is a fix, but a workaround may be to manually upshift in those conditions.

WiscoHR said:

So my random cylinder 6 misfire has returned. Back in August 2016 had a problem with check engine light coming on due to high RPM in 3rd gear. Would push to 4000-4500 RPM and then the check engine light would flash multiple times then it would upshift. It only happens at times from acceleration up steep grades. At that time they re flashed the PCM and no issues. But I live in the flat land of the Midwest.

Now last week it has returned. Finally got a chance to get the JK back out to the hills. Spent a few days in the Black Hills, and every time we were on an uphill grade from a start, I had a choice push to 4000-4500 RPM and wait for the light to upshift or take the hill at 45 mph. Spoke to my dealership in Wisconsin today and obviously they have never heard of it, due to our lack of hills.

So my question, has anyone dealt with this in the past in mountainous areas? And if so what can I tell the dealership to do to fix it?


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Try higher octane gas and see if it changes anything. There could be some kind of abnormal combustion under load, similar to uphill pinging. It's worth a try. It just seems strange that it would only occur under load like that.

Check Plugs. Plug wires

could be just about anything, running too lean, bad injector, plug/wire, coil even a bad cylinder head.

I'd hand it over to the dealer and have them start by checking the cylinder head.

jeeeep said:

could be just about anything, running too lean, bad injector, plug/wire, coil even a bad cylinder head.

I'd hand it over to the dealer and have them start by checking the cylinder head.

Click to expand...

I talked to the dealership today but without the hills around here, there isn't a way to recreate the symptoms. That why I want to see if anyone out west had run into this before. On a daily driving basis it has no effect on me in Wisconsin. But it did help convince the wife that it might be time for a JL.


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Is it Cylinder 6 that is throwing the code? I have had it happen too many times to count. It started within 5,000 mile of my 2015 JKU Rubicon. Dealer couldn't get a code to flash for probably another 5-7K. I am in Utah so plenty of hills. It struggled on those as well as any downshifting to get in to the power band. It finally threw a code and the dealer had the head and lifters replaced. It was running great for about a year until one week before heading to Moab I was in a canyon and sure enough on a down shift the engine light went nuts. I drove it to Moab, and on my way home in the canyon, the light just stayed on. I took it right in to a different dealer the next day and Cylinder 6 flashed again. I left it with them for the day, they said they were was an "update" to run and recommended I clean the fuel injectors. This is all happening before 32K on the odometer. That weekend I traded it in for a JL.

I think the whole "update" was a load of crap, and they gladly took my $250 for the fuel injection service. It was a perfect time to let that problem go, hopefully I haven't got a new one. Fingers crossed!