P0304 Misfire, intermittent idle issues


New member
I got a CEL on my 99 4.0 the other day, for a misfire in cyl #4. Since then I have replaced the plugs, wires, cap, rotor, & CPS.
Jeep drives great at speed, but I can still feel it idling funny. The rpms dont really change but you can feel that its not running smooth.

I tested the resistance in the fuel injectors, they were all the same I think around 14 or so.

I am going to compression test tomorrow, but this jeep has 35k on it Id be pissed if that was the case....

I put some snake oil injector cleaner in this afternoon, and cleared the cel, see what happens tomorrow....

jeep in the middle....jeeps on the left has a trashed pinion bearing & the one on the right has broke a/c, so its been a heck of a week.


New member
Use any coolant?
The 99-03 heads are famous for cracking between #3 & #4, you could be trying to burn coolant.
Check oil condition, too, as water dilution will kill cam bearings real quick.