Easiest way to diagnose misfires?

OP
ejay

ejay

TJ Enthusiast
Joined
Dec 29, 2019
Messages
416
Location
Ventura County, CA
Passed SMOG today. Drove it 100 miles over the past few days with no codes.

What it wasn't for sure: CPS, coils, timing chain, catalytic converters, battery, alternator, or PCM.

Conclusion: I suspect it was an electrical wiring gremlin. Once I ran through the entire harness from sensors to PCM (removing covers and looking for breaks, burns, frays etc.) tested signals on both ends, and put everything back together I had no codes. This was after firing the parts cannon regarding the misfire and O2 sensor heater codes. (New plugs, injectors, upstream O2 sensors)

I'll update if it comes back and I can pinpoint it to a specific area.
 

Kawi413p

New Member
Joined
Jan 4, 2020
Messages
8
Location
California
Here’s a little update. Originally I had a misfire in cylinder 6 and 1 then it changed to 5 and 2. Also a random misfire code would pop up. After the dealership believed the misfire was caused by a worn cam, I pulled mine and found that cylinder 6 intake I think and cylinder 2 intake lobes were severely rounded. The other lobes most likely were worn too. I originally had lifter tick on cylinder 6 and found that the lifter had pumped down. I replaced all lifters back in August and was hoping that would fix my misfire issue. It did not. Regardless, I should have replaced the cam at the same time. Was just hoping the lifters would take care of it. They did not.

Needless to say I now have a new cam, lifters and timing set on the way from enginetech. Hopefully I can put that stuff in and be good. Will update

my timing chain had about 5/8” of slack in it but no marks were on the black tensioner or inside of the timing cover.

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Kawi413p

New Member
Joined
Jan 4, 2020
Messages
8
Location
California
Well, the Jeep passed smog yesterday and has 100mi since the cam swap. I ended up replacing the cam and lifters by going through the oil pan. I had a slight rear main seal leak I needed to repair and after taking the head off once, I decided I didn’t want to do it again.
Since owning the Jeep 88mi was the furthest I got before a misfire. Will update if anything changes. Thanks to anyone who offered advice.