P0301 intermittent

[swaustex]

I spent 5 months chasing a P0306 and an occasional P0301 on a 4.0L I bought in Dec. I spent $280 on a remanufactured head and it fixed it. Valves on the old head where not seating very well. Hard to tell without removing the head. I tried the valve spring theory but they are pretty difficult to take off and put back on, but its damn near impossible to test them with common tools. I did find one push rod slightly bent by rolling it on a dead flat surface. I literally tried to fix it 12-15 times, each time believing I was going to win. Finally took it to a Jeep specialty shop and they said internal engine fault and wanted to put a new head on it. I paid them for their time and did it myself. Head was about $350 all in. Head gasket+Head Bolts+head with valve springs. I reused everything else. Didn't realize how poorly it as running until the new head made it so smooth. I bought the Jeep for a fun side project as a second Jeep so it was a good covid distraction. We all tend to hope the misfire codes are not inside the engine because external parts are more accessible, but in reality swapping the head on the 4.0L isn't that bad or expensive.

Another symptom was relatively smooth startups then it got rougher as it warmed up.

 

[BrunoPizz97]

Update, I did the pump swap and no more P0301. There was a lot of particles in my tank that probably got past the filters and clogged my injectors. Been driving it for 2 days now, no more stutter and no more CEL light. I am happy.

 

[Ephry73]

Glad to hear it fixed the issue OP.

I spent 5 months chasing a P0306 and an occasional P0301 on a 4.0L I bought in Dec. I spent $280 on a remanufactured head and it fixed it. Valves on the old head where not seating very well. Hard to tell without removing the head. I tried the valve spring theory but they are pretty difficult to take off and put back on, but its damn near impossible to test them with common tools. I did find one push rod slightly bent by rolling it on a dead flat surface. I literally tried to fix it 12-15 times, each time believing I was going to win. Finally took it to a Jeep specialty shop and they said internal engine fault and wanted to put a new head on it. I paid them for their time and did it myself. Head was about $350 all in. Head gasket+Head Bolts+head with valve springs. I reused everything else. Didn't realize how poorly it as running until the new head made it so smooth. I bought the Jeep for a fun side project as a second Jeep so it was a good covid distraction. We all tend to hope the misfire codes are not inside the engine because external parts are more accessible, but in reality swapping the head on the 4.0L isn't that bad or expensive.

I truly wish there were better head options for the motor. The Edelbrock unit seems super nice, but pricey (it does shave 40lbs off the block though) and still needs to be worked on a bit.

My p0301 code is still there and I am waiting on the new valve cover and some other parts to replace the springs as mentioned above. If that doesn't fix it, a new head will have to be sourced, or wait for a stroker.

 

[BrunoPizz97]

Glad to hear it fixed the issue OP.



I truly wish there were better head options for the motor. The Edelbrock unit seems super nice, but pricey (it does shave 40lbs off the block though) and still needs to be worked on a bit.

My p0301 code is still there and I am waiting on the new valve cover and some other parts to replace the springs as mentioned above. If that doesn't fix it, a new head will have to be sourced, or wait for a stroker.

I take it that you don’t think it’s your fuel pump or crud in your tank

 

[Ephry73]

I take it that you don’t think it’s your fuel pump or crud in your tank

Funny . Yes I did try the injector swapping when I first got the error and that didn't change anything. Spark plugs and wires as well as distributor cap all changed and still same issue. PO swapped the tank, pump and skid plate months before I bought it from him and I have verified the new parts. There's a good chance it is the valve springs in my case. Once I do the work and flush the coolant(there is some oily residue in the coolant that I am not liking and the PO did have to change the radiator and pump at some point) I will be able to see for sure.

 

[BrunoPizz97]

Update its been about a week now and no stutter or CEL. Problem FIXED!