Misfire #2 p0302

lorenzo.spagna

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Hello to everyone!

I'm Lorenzo and i write from Italy northern.
I have a kj 3.7 limited wich i think have an Electrical issue.
It works not well because i usually have a cyl #2 misfire.
I changed all the coils and the spark plugs.
The compression test it's ok.
The chemichal test of the heads gasket ot's negative.
Every time i disassemble and reassemble the car goes well for few minutes, than turn to go bad.
Any idea?
I read that the cause could be the pcm or the tcm, but i'no idea of where they are and what can i do to check or fix it.
Thaks, Lorenzo
 

basist81

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same here. exactly the same...
misfire on cylinder 2, but not constant - happens once in a while, usually when the engine is hot.
after a long while, multiple/random cylinder misfire error code also pops up (the misfire count is extremely low on other cylinders).
doesn't really have any effect while driving, besides the check engine light.

the engine was overhauled couple of years ago. didn't overheat, didn't break since then.
changed the sparks and the coils, switched injectors between cylinders, checked compression...
local shop didn't find a rootcause of the issue.
seems that the issue is probably coming from the ignition signal from the module...
any thoughts?

Thanks,
Dany
 

LibertyTC

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What spark plugs are installed? Correct factory plugs are best. Ngk ZFR6F-11G Gap .040 inch.
If you pull cylinder 2 spark plug post a photo please. What brand of coil packs were installed?
Carbon build up? Try adding some Chevron Techron Concentrate to fuel & good highway run.
Using a fuel pressure gauge, what are the readings? Key on, running, & off for 15 minutes?
 

basist81

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@LibertyTC - the misfire was there even before the plugs and coils swap. i've went for iridium NGK plugs this time (previously had the type you've mentioned).
coils are NGK as well.
the pressure check was done by the mechanic, and measured pressure on the faulty cylinder (2) was the same as all others.

i'll try to add the fuel addon.
 

LibertyTC

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Ok..Psi on a fuel pressure gauge is? What are the readings? Key on, running, & off for 15 minutes?
What psi readings were recorded for each cylinder? What is the Cylinder compression reading on Cylinder # 2?
 

DadOSix

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this intermittent stuff is where I am a big fan of getting some data recorded from a scope.

The trained tech can determine much from looking at the trace.

Might be a simple as noise ( bad ground) on the harness, or something strange like a valve issue.
 

basist81

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UPDATE
issue root caused.
2 adjusters of the rocker of cylinder 2 were semi-stuck.
replaced those adjusters and misfire is not coming back.
 

tommudd

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Now throw those junk iridium plugs in the trash and get NGK coppers and be even better
 

Noclutch

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UPDATE
issue root caused.
2 adjusters of the rocker of cylinder 2 were semi-stuck.
replaced those adjusters and misfire is not coming back.
How is the labor for this job and what adjusters did you use ?
 

DadOSix

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How is the labor for this job and what adjusters did you use ?
Worst part is getting the valve covers off when I did mine back in ?february?

The swapping of lifters and rockers can be done fairly easily, I think 2 different rotations of the crank, a decent blunt tool to pry rockers. And ‘‘twas done.
 

Noclutch

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I currently have the valve covers off on the 04 KJ, I was in the process of painting them but got caught up doing work on the 03 KJ. Since the valve covers are off I was like I might as well tend to the rockers but this will be my first time doing this job. Thanks
 

DadOSix

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I currently have the valve covers off on the 04 KJ, I was in the process of painting them but got caught up doing work on the 03 KJ. Since the valve covers are off I was like I might as well tend to the rockers but this will be my first time doing this job. Thanks
Check around on here - somewhere there is a thread about the rocker from 04 and earlier being replaced with a revised part. The oil weep hole at the top of the pushrod is bigger in the old style, hence, less oil pressure being kept in the lifter. Ie - easier to have collapse of the lifter. My 06 has newer rockers, but still suffered a collapse. Interesting in that a bath in brake clean dissolved all the crud and it was functional again. But since I went that far, new lifters went in.
 

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