P0304 misfire on cylinder 4

[KJJB]

Hi Folks,
I have a 2010 Liberty thats had a P0420 CEL for several months but has been running great.About 240kkms on it now. Replaced O2 sensors but didnt fix the P0420 problem so its been ignored for the last few months. Recently started getting a P0304 misfire on cylinder 4. Replaced spark plugs and no change. Replaced wires and no change. Replaced coil pack and no change. Any ideas where to look next and/or what it may be?
Thanks

 

[lfhoward]

Sounds like they might be related, although usually a misfire comes first before affecting the cat (unburned fuel is not good for cats). It’s cat bank 1 with P0420 so next step for me would be finding out if that’s the cat on the passengers side, as cylinder 4 is. If they are on opposite sides, they would definitely be unrelated.
(Edit: some googling and I see bank 1 is the drivers side.)

For the misfire code: One thing to try would be to swap the ignition coil for #4 with another unit, and clear the codes. If the misfire code comes back on the cylinder you moved the coil pack to, you know you need to replace a coil pack.

For the cat low efficiency code: Any chance you have an exhaust leak before the cat on the drivers side? You do have a lot of km’s on your Jeep, so maybe the cat is wearing out with age?

 

[KJJB]

Sounds like they might be related, although usually a misfire comes first before affecting the cat (unburned fuel is not good for cats). It’s cat bank 1 with P0420 so next step for me would be finding out if that’s the cat on the passengers side, as cylinder 4 is. If they are on opposite sides, they would definitely be unrelated.
(Edit: some googling and I see bank 1 is the drivers side.)

For the misfire code: One thing to try would be to swap the ignition coil for #4 with another unit, and clear the codes. If the misfire code comes back on the cylinder you moved the coil pack to, you know you need to replace a coil pack.

For the cat low efficiency code: Any chance you have an exhaust leak before the cat on the drivers side? You do have a lot of km’s on your Jeep, so maybe the cat is wearing out with age?

Thanks for the reply. I actually did replace the coil pack with a new one but misfire code came back after about a day. Its possible there may be an exhaust leak or cat might be toast.

 

[LibertyTC]

Welcome to the forums.
What brand of 02 sensors did you install ?
Did you install the correct spark Plugs ?
The KK requires NGK ZFR6F-11 . Gap to be set at .043 inch

 

[KJJB]

Welcome to the forums.
What brand of 02 sensors did you install ?
Did you install the correct spark Plugs ?
The KK requires NGK ZFR6F-11 . Gap to be set at .043 inch

Thanks
O2 sensors are oem
Plugs are OEM NGK ZFR6F-11
Thanks for the reply

 

[LibertyTC]

I would recommend a compression test on #4 to start with, what is the psi reading?