'03 Wangler P301 engine code

[TJDukit]

Ok so my '03 TJ, 4.0L, 67k miles started running like garbage the other day and the check engine light started flashing. I checked the code and it's P301 for a missfire on the number one cylinder. I checked to make sure it wasn't a fuel injector, plugs are brand new. I've decarbonized the engine a couple times and it just got a fresh tank of fuel.

I'd start replacing senors but if I don't get it right soon there are $340 worth of sensor on this thing as far as what my research tells me could be causing the problem.

Does anybody know what is usually the most common cause for this on these. I'm waiting on a crank position sensor since it's the cheapest one, I thought I'd start there. It's the four 02 sensors I'm not looking forward to. I really need this thing fixed before this weekend so any help would be greatly appreciated.

 

[fj40fax]

Do you have a spark checker? I would start there since it is the easiest to check. Then I would run it for a bit and then pull the plug quick to see if it smelled like gas. Last time I had a misfire it was a melted harness going to the injector. Good luck, the scouts are pulling for ya.

 

[grinch]

If not plug try the crank positioning censor. Had something similar happen to me but it was a 303 (3rd cyl misfire)and that was the culprit.

 

[Chevycrew]

we had po302 and po300, crank sensor. It had a brand new one from carquest, after swapping to a gm sensor problem went away, This was on a chevy truck.

 

[TJDukit]

Spark is good and strong, I guess since that's the first thing I always check it didn't seem worth noting. I guess you never know with people though right. What sucks is a spark tester doesn't work very well on these since they have the coil pack and no wires the external testers don't work very well and you can't just remove one plug wire to test it. So I took the coil pack off and made the number one boot miss the plug which gave me a wonderful clicking noise and good spark while it was running.

I ordered a crank sensor today, which was supposed to be in by 3 today but it was not there, after that scouting for deer for Saturday took over my brain and I said screw it for today.

I'll swap in the CPS tomorrow and see what that does. It is nice that it happens to be the cheapest sensor on this thing.

The good news is we did see a few bucks and one really nice one, I think he is gonna get popped on Saturday and I'm gonna try to get it on tape. Too bad I'll be the one with the camera.

Thanks guys, if all goes well this thing will be running good for Friday and I'll get home in time to get 4 hours of sleep before deer season.
If the crank sensor doesn't fix it I guess it's on to o2 sensors.

 

[grinch]

Well I hope that's it. Not only is it the cheapest censor its also easy to replace considering some of the other options. Let us know if that works I always like to try and keep up on problems and answers in case I run across them again in the future.

 

[Toad]

Compression?

 

[Toad]

Injector pulse?

 

[TJDukit]

I feel stupid now. I changed out the CPS with no luck. So I took a step back and decided to dumb it down once again. I swapped the number 1 and number 2 plugs and guess what it started missing on the number 2 cylinder. What really gets me is that these plugs aren't even two months old and they are E3 plugs which I will never be buying again.

Went to autozone picked up some autolites and put them in. Good to go. I'll have to drive it up Farmington tonight to get some miles on it to make sure it's not something else fouling up the plug but I think it's good to go.

 

[TJDukit]

Well we made back and the Jeep is still running great so it looks like problem solved. Thanks guys.

 

[eatrocks]

E3 plugs I have found that most of the great high cost plugs are not worth the extra cost

 

[Toad]

good to know that e3 plugs suck. I had been thinking about trying them out.

 

[TJDukit]

I've been running the e3's in my '03 sierra for well over a year now with no issues. I've even been getting better mileage since I put them in. Even so I will never buy them again.

 

[Silly Willy]

I've been running the e3's in my '03 sierra for well over a year now with no issues. I've even been getting better mileage since I put them in. Even so I will never buy them again.

I too have gotten better millage, only thing is I now run very rich.
but I as well would never get them again.