I have an 07 jku that is undrivable due to engine issues. It started out seeming like it had bad gas, when it wud start missing I cud floor it & it wud clear up. I used Seafoam in the next 3 tanks of gas & it only got worse. The only code it has ever thrown is P0300. I’ve changed everything imaginable including the computer. Plugs, plug wires, coil pack, crank sensor, cam sensor, timing chain & gears, head gasket, intake gasket, had injectors tested, ran compression test, fuel pump pressure test (without engine running). And it still can’t be driven. It starts fine when cold, but after the high idle kicks off it starts missing & will backfire thru the intake. Also when I try to start it after it’s warm it drags like the timing is off (thus the reason for new timing chain & gears). Had a left bank head crack last year & replaced it & the headgasket on the right bank as well. It ran perfect for several months after that repair before this started.

 

Sounds like a fuel delivery problem, JMHO

 

I had a the same code and changed out my bosch plugs for middle of the road NGK ones and was good.

 

I don’t disagree with you that it’s possible. Pressure wise the pump is doing what it’s supposed to do. What information I haven’t been able to find anywhere is how much fuel it’s supposed to pump (volume) at that pressure while it’s running. I did forget to say that if I crank it & just let it idle it will still have the mis, but will idle all day. The issue starts as soon as I put it in gear & try driving it. Once it’s above an idle the mis is so bad it won’t pull itself

 

The code # it’s giving really isn’t what I’m concerned with, but more the fact that the Jeep is undrivable. Every post I’ve read from people that fixed their problem by changing to a different brand of plug, weren’t having an issue that kept the Jeep from being able to be driven, but that theirs ran rough & needed to fix a minor misfire. My Jeep will not pull it’s self on flat ground without being in 4Low it’s missing so badly. But as far as the spark plugs are concerned when I replaced them I used champion platinum plugs. I will add though that I can crank it up & it will sit & idle all day, it still has the miss, but it will idle the problem comes when I try to drive it & have to get above an idle

 

Missing that bad under load and just a generic misfire code not specific to a cylinder sounds liek a vacuum leak. You might want to go over all your vac hoses and fittings.

 

• Quote:

  Originally Posted by Ghost JK

  Missing that bad under load and just a generic misfire code not specific to a cylinder sounds liek a vacuum leak. You might want to go over all your vac hoses and fittings.

i have went thru them several times, including the plastic upper intake

 

If you have a clean gas can, disconnect fuel line at injector rail, see how much fuel is flowing. It should flow a pretty good stream

 

Plugged cats maybe. Sounds like fuel supply issue to me as well

 

I did remove the cat’s to be sure that wasn’t the problem as part of the long list of things I’ve tried. Fuel pump pressure is good, so it would have to be a volume issue with the pump. That’s probably the 1 thing that I haven’t tried.