Hello everyone, looking for some advice. Yes, I've looked into the issue and read a bunch of threads and have like 5 different directions to take so I'm hoping someone can lead me in the right direction!

Symptoms: Jeep will run start fine and run great on my daily commute, 30 miles on the highway. Once I get off the highway and let the rpms go to idle it starts to misfire and the engine light blinks. I turn the jeep off, restart it and it runs fine. It has a rougher idle which it didn't have before this, but I doubt most people would even notice it. I had the code checked and it said Cyclinder #6 misfire, but I don't believe that is the actual issue. I replaced the coil pack and spark plugs (NGK) with no change.

The fact that restarting it makes it go away is what's confusing me and I'm hoping someone will understand what that means ha

After my research on here I've seen people mention crank position sensor (CPS), idle air control (IAC), and throttle position sensor (TPS) as potential causes.

Also, it's not heat soak. Ran fine all summer even in 100 degree days (70's now). And I have hood vents to get rid of some of that hot air.

Any help is much appreciated!

 

Any thoughts guys? I searched for days and finally found a couple other posts stating the same exact problems but the owners never said if the issue was fixed or how...hate that

 

Can you get your hands on a OBD2 scanner? One that will provide real-time data while you drive? If I were in your shoes, the next thing I would want to see are my fuel trim values (short term and long term) during my drive.

If I had to take a wild **** guess, from here, I might think that there is an O2 sensor problem and the fuel trim is changing during the long, fast, hot part of the drive, but then is not adjusting properly when the conditions change. Restarting might be giving the computer a chance to recheck the sensors and select a default fuel trim (it chooses a fuel strategy for each startup). Just a guess, but we have to start somewhere.

Could be CPS as well, but I would think it wouldn't just happen after coming off the highway and magically go away on a restart.

It could also be a IAC that is gummed up and getting sticky when it is warm. When was the last time you cleaned the throttle body and/or replaced the IAC?

 

I just ordered a OBD2 scanner (https://www.amazon.com/BlueDriver-Bl.../dp/B00652G4TS). Supposed to arrive on Tuesday so hopefully that will tell me something.

A new problem it's developed today is when driving on the highway it feels like the engine is falling on itself or the transmission is slipping - I can see the rpm's increase when it does this. I'm guessing it's related, I mean what are the chances of transmission slip at the same time as all of these issues? ha

Thanks for the suggestions. I've never cleaned the throttle body or replaced the IAC. I'll go throw some parts at it this weekend. I'll try the IAC first, then CPS, and hopefully have time to clean the throttle body. Thanks!

 

when you get a flashing indicator and a solid miss in a specific cylinder i would be inclined to believe that you have a cylinder 6 misfire. You may want to check compression and maybe swap the #6 injector with another one. and although NGK plugs are some of the best plugs you could by I would also swap the plug with a different cylinder than the injector. the three causes you mentioned dont tend to only target a single cylinder and you would usually end up with other faults or at least a P0300.

Restarting the car may make the problem go away because when then vehicle detects a misfire it is likely killing that cylinder off to prevent further damage, either by disabling spark or fuel which gives it a dead miss and a flashing light.

Unfortunately given the year jeep that you have you might have an issue with the cylinder head. it may either be cracked or may have a bad head gasket. but check all other issues first.

 

Do a compression test and leak down test..u most likely have a mechanical issue in that cylinder..could also be ignition as well..start with the cheap.stuff and check plugs and wires then do the compression test

 

Okay so an update. I used the code reader this morning and tracked O2 sensor voltage when the issue would appear. When it began misfiring the O2 sensor bank 2, Sensor 1 and Sensor 2 was reading 0.02 and 0.04 V, respectively.The O2 sensors in bank 1 were reading normal around 0.7/0.8 V.

The codes it's throwing are Cylinder 1, 6 and random misfire. I don't know what the low voltage is telling me, if anything....would appreciate some input. Thank you!



Also, the jeep has about 153K on it and it's a reman engine (different style head) that was put in around 100K.

 

Following.

(Sorry, no advice. Just want to be able to find this one easily when you update.)

 

It would require modification to the head to allow for the coil pack, you sure it's a different style head. Either way its not horribly important at this time. it might benefit to pull the plugs from the affected cylinders and take a look at them, you may find some indication on them as to what might be the cause. if it's fuel related any way. If there is a misfire counter that you can access you should be able to assess which cylinder is misfiring the most.