08 JKU auto with 75k miles.

I have suddenly started feeling a slight misfire (I believe) when my Jeep is warmed up and sitting at idle. I say I believe due to the fact that the computer is not throwing any codes, but it feels just like a misfire to me. The exhaust note has a slight hitch, a light shudder runs through the jeep, and if several happen in succession you can watch the tach stumble from 700rpm down to 500rpm, then back up. It sometimes feels like the engine is about to stall.

I realize I can begin replacing the usual suspects: EGR valve, plugs, wires, coil packs, etc., but I'm stumped by the fact that I am not throwing any codes. I thought these computers were super sensitive to reporting things like misfires. I'd hate to replace parts for no reason and then find out I am running completely in the wrong direction.

It began very sporadically and has become more frequent - it also happens more often in Drive than in Neutral, so I suspect the parasitic drag from the torque convertor is helping to trigger it.

I'm running a flashpaq in 93 octane performance mode - I did try flashing back to stock and it made no difference.

I ran seafoam through the brake booster vacuum line and replaced the PCV last year (to try and decrease oil consumption - didn't work). And when this began happening I did a thorough seafoam throttle body cleaning as well. The misfire only seems to occur at idle, never while driving under load.

Any ideas?

 

Man I have a thread going right now for a very similar issue. 08jku running 93 octane for tow tune and it started around the same time I ran seafoam through the vacuum line. During seafoaming my ecl stated flashing but hasn't since. My idle is fine however if I sit and idle for awhile I will feel on occasional light "kick" like a misfire but no codes are being generated.

For me, it is happening primary when lightly accelerating or "cruising". Out of nowhere I will feel it jerk /bump 2-3times in succession. Almost feels like the transmission bucking but my transmission is otherwise shifting as smooth as ever. Not noticed any significant change in rpm when it happens but may just not be catching it

Im pretty stumped too. Really hope it's not transmission related...i don't think it is. My plugs /wires only have maybe 15k miles on them.

Anyways, it seems like there are a lot of things that can cause it, transmission, ignition issue, sensor, fuel pump, even bad gas

Not yet sure how I am going to approach it. Hate to start throwing time and parts /money without knowing exactly what the issue is. With no codes and it happening intermittently, I don't am afraid a shop or dealership would charge me 100$ for diagnosis and come up with nothing

Ugh. I just want a code!! Lol

Hopefully someone will hop in to help you and I can see if it helps my issue as well!

Good luck!

 

My daughter just called me today. Her 2014 JKU started jerking and the CEL started flashing. She shut it off, restarted, no more CEL. Had her check for codes, no codes.
She's bringing it to dealer tomorrow. She's only got 7000 miles on it.

 

If the CEL was flashing it was defiantly misfiring. Odd that it didn't store a History misfire DTC though.

 

A tech would probably hook it up to an OBD scanner, that's what I'd do as well -- Look for pending codes, as well as the various parameters. Another thought would be to find a long hill and see how it responds to an Italian tune-up (full throttle power under load).

 

I hadn't heard before that there might be 'pending codes'. Do you know if the scanner they use at Autozone can read those types of codes?

 

There's a wide variety of scanners and code readers with various functionality -- Suggest asking what they have, and then look up the manual for it.

 

Spark plugs on my 07 were shot after 50K miles. Electrode was worn down to a fine point on 5 of 6 cylinders. They weren't oily or burnt, simply worn out.

Symptoms came on slowly, the stick shift would wobble at stoplights. RPM would drop from 800 down to 400, stumble then float back up.
Then suddenly over 2-3 days it got bad, really rough idle when cold and stumbling under acceleration. Felt sluggish and slow all the sudden.
I thought I had bad fuel, maybe a clogged fuel filter, or worse OH GOD MY 3.8L must have a blown head gasket! Doom and gloom washed over me.

Nope, it was just plain old spark plugs.

Replaced all 6, she ran fine.
Actually ran quite a bit better. I just failed to notice the slow loss of power and poor gas mileage.

 

Had this same problem once when my jeep was new , water in the fuel tank . . . I was freaking out .. took it to the dealer they found the problem .. it was brand new and took it Devils garden for the weekend. I never swamp the jeep but the water was very deep and at time over the hood .. after that I rerouted all the breather hoses . .

They said it had to come from a gas station on one of the fill up had no codes and thought I really screwed something up . . during the rainy season 32 to 46 inches of rain ... and that's a dry years

 

I had this happen recently. After seafoam and PCV valve I did a compression test and while doing the test discovered that one of the plugs had come loose. I decided to replace all the plugs and has been fine since. I've never had that happen before. It's worth checking.