P0304, P0306

[Root Moose]

So, I put a red top in the MY01 on Sunday and within an hour or so it threw misfires in number 4 and 6. I was towing a ~3k trailer at ~50 mi/h at the time. Was actually pulled over and idling when I noticed the code.

Coincidence/red-herring or?

I just bought a reader tonight and reset it so I don't know if they will re-occur yet.

What could cause a misfire? Those were the only two codes.

[Root Moose]

Drove it to work today (~35 miles).

No new CEL.

<shrug />

[langer1]

code P0304 P0306 may mean that one or more of the following has happened:
Faulty spark plug or wire
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector
Burned exhaust valve
Faulty catalytic converter(s)
Running out of fuel
Poor compression
Defective computer

[Root Moose]

Hmm, lately the Jeep is "hard to start", as in long cranking time.

Maybe poor fuel delivery because fuel rail/pump is not moving enough gas?

[langer1]

I would look at weak spark first, a redtop battery charges at a lower voltage and could cause a weak spark to be more noticable.

[jneary]

how many miles on the jeep and how long since the last tune up

[Root Moose]

how many miles on the jeep and how long since the last tune up
It's due for a new set of plugs. It has 100k mi on it.

[jneary]

in some of the newer 4.0s chrysler is using NGK plugs for eroneous misfires. i would check to see if this applys to your jeep

[Talyn]

The NGKS helped with my hot start issues.

The 00-01s are known to have two problems associated with starting.

One is that after a hot soak you start it it will throw a fismire code. IIRC it was on cylinder 3. The TSB involves installing a heat shield on that injector. I have it and it works

There is also a computer reflash for the cold start issue which I have not yet had done. The more mods I did the worse my cold start issue is. I usually remote start it in the mornings and let it run fro 10-20 seconds before I drive it. If not the engine seems like its bogging down and ocassionally I get a back fire.

Another TSB suggest excessive carbon on the valves. Run a Mopar CCC or a Seafoam treatment for this.

-Chris