I know, it's a common misfire thing...

[forcefed44]

Followed and read every post and Youtube video out so far @ 167K

BUT.......

I have been having a idle misfire for a while and replaced parts that I have read, first off I did a compression test to make sure to see if there was a bad cylinder. Everything checks out fine as per ratio measurements and have no tapping noises. Now my misfire is only at idle and very slight hesitation from initial take off only. Power delivery through the rev band is strong through out. Pulled code and only one codes came up for random misfire.


So this is my list of parts replaced in order:

*6 ignition coils
*Copper plugs
*Chevron Techron

no change in idle miss. check engine light came back on

*crank sensor
BP 93 and drive light I stole it.. LOL

slight improvement but only minimal, check engine light came back on. Same misfire code

*all 6 injectors
*cam sensor
*cleaned throttle body

Idle smoothed out alot but still has a miss at idle. Code P1391 came on, checked everything (CPS and Crank sensors, all good; cleared light and did not come back.


Next but not done yet:

*IAC valve sensor
*new PCM flashed for my truck

Now this actually happens more when the engine is at operating temperature. I have seen a test someone used and found out that the signal driver to the PCM for the injector was bad and that person also swapped the ECU. Is this what it is? I have not touched the IAC sensor or the TPS. Someone help me please.

Chris..

 

[renegade 04]

did you check the pcv system and make sure its working. another thing could be to replace the TPS because they sometimes develop a dead spot on them and can cause problems.

 

[forcefed44]

did you check the pcv system and make sure its working. another thing could be to replace the TPS because they sometimes develop a dead spot on them and can cause problems.

I will check into the TPS.. I figure it's one of the last sensors. I did the PCV valve and checked all the hoses that are linked to blockage and build up and nothing. Suprisingly the engine is really clean.

 

[tjkj2002]

I'd be looking at the cat's...................

 

[J33Pfan]

clean out your fuel rail

send out fuel injectors to get prof cleaned

 

[Damotee]

O2 sensors?

 

[forcefed44]

clean out your fuel rail

send out fuel injectors to get prof cleaned

I just installed brand new injectors (not refurb or cleaned) and has a full fuel system cleaning. I'll look into the rail when I get deeper in.

 

[forcefed44]

O2 sensors?

Wouldn't that throw that code on the dash? last code came up was for the Cam sensor.

 

[teeje]

Put in some marvel mystery oil. Sometimes the carbon buildup will not allow the valves to seal causing a misfire. May take some time but to work it's way through but it may work. You can also try sea foam. Take the brake booster vacuum line off and slowly pour it in there. I've done this on my old engine and had the EXACT SAME issue you had and that fixed it

Sent from my SM-G935P using Tapatalk

 

[ltd02]

What year do you have? Could just try cleaning the IAC before replacing.

 

[LibertyTC]

Two bottles of chevron techron concentrate in fuel and take it for a good hwy run 100 miles, to clean back side of valves.
I also have used MMO in fuel at the same time. Jeep liked that.
Info re TPS link:http://www.jeepkj.com/forum/f196/throttle-positiion-sensor-replaced-tps-59336/
Ya what year jeep? Clean the IAC & port etc.. link see post 10: http://www.jeepkj.com/forum/f196/idle-air-control-no-screws-44826/#post475141

 

[J33Pfan]

Two bottles of chevron techron concentrate in fuel and take it for a good hwy run 100 miles, to clean back side of valves.
I also have used MMO in fuel at the same time. Jeep liked that.
Info re TPS link:http://www.jeepkj.com/forum/f196/throttle-positiion-sensor-replaced-tps-59336/
Ya what year jeep? Clean the IAC & port etc.. link see post 10: http://www.jeepkj.com/forum/f196/idle-air-control-no-screws-44826/#post475141

@libertytc

so with 167K mi on it which sensors should be replaced just because its time is over?

i didnt know o2 sensors can last that long. are they still accurate at that mileage?

 

[forcefed44]

What year do you have? Could just try cleaning the IAC before replacing.

6/2002. I figure since it was cheap, to just replace.

 

[forcefed44]

Put in some marvel mystery oil. Sometimes the carbon buildup will not allow the valves to seal causing a misfire. May take some time but to work it's way through but it may work. You can also try sea foam. Take the brake booster vacuum line off and slowly pour it in there. I've done this on my old engine and had the EXACT SAME issue you had and that fixed it

Sent from my SM-G935P using Tapatalk

I will try the seafoam or MMO..

UPdate*

Drove it today and it ran lovely as usual but as soon as I came up to a traffic light after a 40 mile 70mph run; the check engine light came on. I put my scanner on and it read P0305 #5 cyl misfire and P1391 P Cam Position sensor again. I will pull the plug and make sure it's getting the correct power signal and/or re-install the old Cam position sensor tomorrow and take it for a drive with the MMO also.. MMO in engine and fuel tank?

Also, while I have the manual out in front of me. Would a leaking intake manifold runner O ring gasket make the misfire happen at idle or throughout the RPM band?

 

[uss2defiant]

1. did you install a mopar CPS? aftermarket ones are known to be crap. a lot of experiences here.

2. MMO in fuel tank

3. sorry. don't know the answer to your last question.

 

[forcefed44]

1. did you install a mopar CPS? aftermarket ones are known to be crap. a lot of experiences here.

2. MMO in fuel tank

3. sorry. don't know the answer to your last question.

Unfortunately, my local Dealer was uninterested in selling me or looking up the part when someone walked in asking for side steps for a 2017 Rubicon. I ended up buying a Standard brand part from Napa which usually had good experience with.

 

[J33Pfan]

Unfortunately, my local Dealer was uninterested in selling me or looking up the part when someone walked in asking for side steps for a 2017 Rubicon. I ended up buying a Standard brand part from Napa which usually had good experience with.

Ive had bad experiences with standard parts with other makes/models.

Ive banned their parts from all my cars

 

[forcefed44]

Ive had bad experiences with standard parts with other makes/models.

Ive banned their parts from my cars

Unfortunately, if you need to try things, and that is the best that will do. I use it. Better than Autozone branded parts IMO.

 

[ltd02]

I'd definitely try to get a Mopar CPS. That might fix all these problems. I like the Techron and the MMO too. Oxygen sensors can last a long time, unless something contaminates them. I've only replaced one downstream sensor on my 02 with 179k and I'm almost positive the others are stock.

 

[forcefed44]

SO I decided to go through the whole truck at my shop instead of just chasing a ghost and after test after test and diagnosis.... It's Solved and runs great. Always will have a slight idle miss but nothing like before, no codes, vibes, valve problems, jumping idle etc.. Borrowed a FCA reps '10 KK with 40K and mine idles better than his. Picked up another KJ with 200K body and 20K reman 3.7 and that has the same idle as the KK.

Chuffed..

Thanks.