Misfire on cylinder 5

jacobmccleery

jacobmccleery

New Member
Joined
Feb 17, 2020
Messages
4
Location
Miami, OK
Last week I was headed to work when I started getting a misfire and the check engine light started flashing. I also had a warning that read GASCAP, although I’m not sure that this is related to my issue. First I bought some spark plugs because I wasn’t sure how old mine were, the plugs pretty much fell apart so I replaced them too. Still misfiring, I got a new coil pack and tried her out and the misfire was gone! I let her run for about 10 minutes, all good so I proceed to go check cows. I run into a bit of mud so I give her a little gas, misfire is back. Any ideas or suggestions? My next step would be fuel injectors, but the it kinda baffled that the new coil made the issue go away temporarily.
Thanks in advance -Jacob (2008 JKU)
 
Scan it with an OBDII scanner and tell us which codes exactly it's throwing.

What brand of coil pack did you use for the replacement? What spark plugs did you use? What did you gap them too?
 
Chris said:
Scan it with an OBDII scanner and tell us which codes exactly it's throwing.

What brand of coil pack did you use for the replacement? What spark plugs did you use? What did you gap them too?
Click to expand...

The code it’s throwing is p0305. I can’t remember the brand of coil pack but it was the pricier one at oreillys (not mastercraft). The plugs are champion gapped to .050.
 
I know that often times the aftermarket coil packs can have issues with them. It would be worth testing the coil packs using this method:


I realize that is for a 4.0 TJ, but the same principal applies for any vehicle. At least this way you can rule out whether or not the coil pack(s) are the issue. You'd be wise to start here first, as Ockham's Razor would state that the simplest solution is usually the right one.
 
So I had to wait a couple weeks to get it in a shop, but the coil pack is good and all the injectors are working properly. Had them do a compression test and all the cylinders match. The mechanic is now suggesting it’s an issue with the ECM. Does that sound right? I suppose that would explain it’s been an inconsistent misfire.
 
It could indeed be an issue with the ECM, yes. I believe they should have a way of testing the ECM though per the FSM (Factory Service Manual), so I would ask them to test it before jumping to conclusions.
 
Did they eliminate the possibility that there is a problem with the wires. Being inconsistent misfire would make me wonder. Replacing parts might have jiggled the cables in a good way and the mudding may have jiggled them in a bad way.
Don
 
If it was my Jeep and before spending more money i'd swap no 5 plug and wire with another cyls plug and wire and put 5's plug and wire on that cyl. Reset the CEL and see what happens, most that could would be the problem stays on no 5, if it does be sure to switch the plug wires back where they belong if they are numbered.
 
Hey Jacob, I’m also looking for answers to this issue although with a 2013 JK 3.6 Penestar unit. I’m experiencing the same issue. All looks good and longest amount of days driven without EML ON was 156 days now it’s down to 6 or 9 On average. To me that would suggest electronics. You mentioned PCM unit, where I’m suspecting my issue lies. I’ve also heard of PCM’s being tested and returned as NON FAULTY yet there is a fault with it and being corrosive soldered joints which will be effected by temperature. Can you give an update to your initial issue and I’m assuming conclusive repair... ? Thanks 🙏
 
Top Bottom