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Discussion Starter · #1 ·
Hello.

I have been chasing a P0300 and a P0304 code on my ‘05 LJ 4.0 6spd about 2 months after I bought it over the summer and I can’t seem to figure out what it is but it seems to be electrical.

I have checked my spark, done a noid test, and did a basic spark plug tune up but nothing seems to be fixing the problem. That being said, the reason I say I think it is electrical is that the code shows up as injector 4 no matter which injector I have the connector plugged into.

I did read that it could be a possible bad cam sensor but when I install the new one, it immediately starts surging and throwing a cam sensor code so I am not sure what I am doing wrong. I am a diesel mechanic by trade but this is making my head spin.

Thanks in advance!
 

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Aftermarket sensors are iffy. Apparently the MOPAR ones have changed as well as I have seen people reporting issues with them too.

You need to check the Oil Pump Drive Assembly (OPDA) for wear and/or seizing. Known issue on the 05 and 06 models. Search the forums or google for OPDA removal instructions and the issues.
 

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Are you saying the noid test shows #4 injector is firing but sill showing a misfire?

Is it actually misfiring or just showing the code but running smoothly?

As noted above, any non original cam sensors (even new ones from the dealers) are suspect so hopefully you saved the old one. If so put it back in the OPDA. They rarely go bad & usually not affecting only one cylinder if they do fail.
 

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Discussion Starter · #4 ·
Aftermarket sensors are iffy. Apparently the MOPAR ones have changed as well as I have seen people reporting issues with them too.

You need to check the Oil Pump Drive Assembly (OPDA) for wear and/or seizing. Known issue on the 05 and 06 models. Search the forums or google for OPDA removal instructions and the issues.
I pulled the cap off of the OPDA and compared the “play” to a brand new one and it was the same so I don’t think it’s bad.

Are you saying the noid test shows #4 injector is firing but sill showing a misfire?

Is it actually misfiring or just showing the code but running smoothly?

As noted above, any non original cam sensors (even new ones from the dealers) are suspect so hopefully you saved the old one. If so put it back in the OPDA. They rarely go bad & usually not affecting only one cylinder if they do fail.
The noid light lit up and increased in speed as I moved the throttle cable but I didn’t compare the light to any of the others. To answer your question about the sensor and code, I put the old sensor back because I couldn’t drive otherwise and it is misfiring at idle but when I’m driving, I don’t feel it at all.
 

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What makes you think it is an electrical/injector problem?

P0300 is random cylinder (non specific) misfire & P0304 is cylinder 4 (non specific) misfire. There can be various reasons for those codes. Normally if it was injector specific it would be a different code like maybe P0204. Also, if the injector was not firing you would get a dead cylinder & a very rough idle & low power when driving (only 5 cylinders firing). The misfire codes (P030x) can be from a weak cylinder, not necessarily a dead one.

I would look elsewhere. Doing a compression check would be a good place to start.
 

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Discussion Starter · #6 ·
What makes you think it is an electrical/injector problem?

P0300 is random cylinder (non specific) misfire & P0304 is cylinder 4 (non specific) misfire. There can be various reasons for those codes. Normally if it was injector specific it would be a different code like maybe P0204. Also, if the injector was not firing you would get a dead cylinder & a very rough idle & low power when driving (only 5 cylinders firing). The misfire codes (P030x) can be from a weak cylinder, not necessarily a dead one.

I would look elsewhere. Doing a compression check would be a good place to start.
I just assumed it was an electrical issue because it still showed up as Injector 4 no matter which injector connector I had plugged into injector 4 but I will try a compression check.
 
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