OK, heres the story. The van runs fine, has about 145,000 miles on it - It feels a little rough at idle, but it is NOT noticeable to an ordinary driver...

Problem: MIL, small miss, OBD-II PCM code P0304 (Cylinder 4 misfire).

History: Attack of the killer woodchuck; ate through the plug wire set. Upon install of the new wire set - noticed an 8-way connector (FI harness) below the coil that had all the wire insulation either worn, melted, or chewed away - still intact - but I am sure some of the wires were touching each other - as there was really no way they could not be.

Repairs done: Went to dodge to get new 8-way connector, 1/2 was the set that goes to the 6 injectors, and 1 wire to ASD relay - other 1/2 goes to main wiring harness - fuel injector side, $80.00, harness side connector, $1300.00, my looks and comments to sales-droid... PRICELESS. GRRRRRRRRR.......

I remove each wire on the 8-way and use insulated male/FM spade connectors and then electrical tape them up - just like new - and only $6.00 - not $1600.00. I install premium wires, cap, rotor, and NGK platinum plugs. Before the incident it ran fine, and I don't remember a MIL being on. After the woodchuck attack, and post repair, it now starts and runs just fine - I feel slight miss, but nothing I would even notice - had the MIL not been on. I get the P0304 #4 cylinder misfire - so I do some more checking and I pull the upper intake, fuel rail, and other associated parts and pieces and I replace the #4 injector with a brand new unit. Put it all back together, and DRB pressurize the system - only to find out I nicked an o-ring on one of the injectors placing it back in - gas shoots across the shop - GRRRR... Pull the top of the intake off - AGAIN - and pull injectors and re-o-ring them again - this time being really nice, and then DRB pressuring after I put the rail back on - but BEFORE I put the intake all back together - no leak! Yippie. Shew.

Start up, runs fine - as usual. After a pair of drive cycles, MIL P0304 comes back - again. GRRRRRRRR....

Reset MIL and swap #4 plug wires - to verify. Re test drive, and P0304 returns.

I guess Ill try checking compression later this week - but it runs fine, and the miss is barely noticable.

Could the coil be bad? Its only one coil - I can see that being bad, IF it runs fine, and the misfire never changes to another cylinder. I would think either all or none? Am I right?

Anyone ever run into this before? I hope the PCM did not get damaged by a possble ground/short on the 8-way FI harness - Ill have to do some more checking. Just trying to see if anyone else has run across this - I don't want keep chasing my tail if someone says "ohh yea - been there done that". I hope I have provided enough info.

Thanks!

Eric

 

What about the possibility of a bad coil pack? A drive mode computer also might help you isolate when and why this occurs. A Snap-On MT2500 would give you drive mode diagnostics, if you know someone you could borrow one from.

 

The coil pack was on my list - but I don't understand how it could be bad only on #4; when I have swapped the wires, and it stays with #4 - I would think that the single coil would cause it to either move around, or fail all together - but not stay on the same cylinder. Am I wrong on this thinking? With it staying only on #3, and with all the other secondary ignition and FI being replaced - I am almost left with a feeling of it being an internal engine problem? But since its not that pronounced, or almost non-noticable - it could have also been a damaged PCM by the wiring issue. Ill do some drive tests - I just ordered a brand new scanner to do some more captures. Ill keep everyone posted.

 

Yep, been there done that.
My 3.0 with 147K had low compression #4 cyl. 75psi. Leak down test had air coming out ex. burnt valve.
As yours, myeng. ran fine off idle. Mine had same code and cyl.
Could of just taped up the harness.

 

BTW no coil pack on 3.0 Just one.