Jeep Wrangler PCM and module repair and replacement

P0304 Code

Alatex

Alatex

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Jeep has had an issue where on startup a slight knocking sound would occur occasionally and increase or decrease with RPM. Then when warm it would go away.

Hasn’t happened in a while but today I started it up and the knocking was present and as I pulled it around the yard the CEL light came on. Did the ignition test and got P0304.

Spark plugs and 02 sensors are a couple of years old. Where to begin?
 
Misfire on cylinder 2.

I'd put a screwdriver on the injector and up to your ear and see if you can hear it clicking.

I'd definitely pull the plug and "read" it.

Might be time for a compression and leak down test.

-Mac
 
Found an injector connector that appeared to be burned and had exposed wiring, replaced the connector and nothing has changed. Attached a video to see if anyone can diagnose the sounds
 
Alatex said:
Found an injector connector that appeared to be burned and had exposed wiring, replaced the connector and nothing has changed. Attached a video to see
Click to expand...

The video needs to be uploaded to YouTube or Vimeo and then you'll copy and past the embed code here.

Forgive me for being obtuse, but did you clear the code after you made the fix?
 
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Chris said:
The video needs to be uploaded to YouTube or Vimeo and then you'll copy and past the embed code here.

Forgive me for being obtuse, but did you clear the code after you made the fix?
Click to expand...

I did not, just judging it based on how it’s running
 
Alatex said:
I did not, just judging it based on how it’s running
Click to expand...

It could be there is more damage somewhere to the wiring harness.

This is one of those instances where I would want to hook it up to a tool that can do live diagnostics and provide real-time data. When you watch the data in real time as it's running rough you can pinpoint much easier what the actual issue is. I say this because P0304 can be caused by a multitude of issues such as:
  • Ignition system problems
  • Fuel system issues
  • Mechanical issues
  • Vacuum leaks
  • Faulty spark plugs
  • Ignition coils
  • Fuel injectors
  • Wiring fault
Just to name a few.
 
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Had a little time to mess with the jeep again today and now I’m getting P0300, P0301 and P0304. Coil pack?
 
Replaced plugs and coil pack, started it and everything seemed to be fine, then the shuddering and rough idle started back. Did the screwdriver trick and all of the injectors seem to be operating
 
macleanflood said:
I'm hoping you can read PIDs like fuel trim and vacuum.

-Mac
Click to expand...

I will borrow one from a friend tomorrow if I can’t get mine to work. Is it possibly a head gasket but no coolant in oil, no smoke?
 
So after thinking about these issues, it seems as if this is more of a sudden thing and maybe happened right after getting fuel. Could all of this be caused by some sketchy fuel? Thinking of treating the fuel and seeing if it changes anything
 
It's all speculation without data.

I'll say sure, sure it can be whatever you think it might be. Everything is possible.

What we need is data. Live data from the Jeep's PCM. That's what's going to solve this puzzle.

-Mac
 
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Ok I have a way to look at live data, what exactly should I look for?
 

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