P0301 intermittent

BrunoPizz97

BrunoPizz97

TJ Enthusiast
Joined
Jul 11, 2019
Messages
408
Location
Long Island
Hey guys,
I have an issue that needs some solving. I've got a 97 TJ and its throwing a p0301 code that wont go away.
3 months ago I had the motor swapped, because as most of you know I blew it up. Anyways, the new motor that went in was completely reconditioned by my jeep mechanic. It was running great with no issues at all that is until I took it on its first trip, going to my destination was a breeze; I drove around the town I was in and it was running like a dream. When I went back home 160 miles I had no issues, the next morning I start it up and it begins to sputter for 10 seconds and smooths out. I reset the computer because I assumed it was Vapor lock, I ran the car pretty hard and as soon as I got home I shut it down. So I didn't get the code for a while until a couple weeks after, so I went to auto zone read the code and it was P0301. I hit up my jeep guy he says that it may be my fuel pump is bad and we have known about the fuel pump being weird through out the life of this jeep. He thinks I may have something clogged in my fuel lines, he suggested that I change my pump and blow out my lines. What do you guys think I am obviously going to change out the pump because I have to prime the pump when I want to start the car up.
 
Why would a fuel pump only cause a cylinder #1 misfire? Makes zero sense.

All at the same time, swap plug 1 with 2, swap plug wire 1 with 3 and swap injector 1 with 4. Now see where the misfire moves to. If it doesn't move check the injector 1 wiring.
 
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CodaMan said:
Why would a fuel pump only cause a cylinder #1 misfire? Makes zero sense.

All at the same time, swap plug 1 with 2, swap plug wire 1 with 3 and swap injector 1 with 4. Now see where the misfire moves to. If it doesn't move check the injector 1 wiring.
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I used to have a problem where i would get some kind of gunk clogged in my fuel rail and it would clog my injectors. He assumes that i have something messing with my fuel pressure. The fuel rail begins at cyl 1 and the line runs to 6, he thinks that i must have something in there.
 
BrunoPizz97 said:
I used to have a problem where i would get some kind of gunk clogged in my fuel rail and it would clog my injectors. He assumes that i have something messing with my fuel pressure. The fuel rail begins at cyl 1 and the line runs to 6, he thinks that i must have something in there.
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Then take the rail off and blow it out, but I still don't see has his original suggestion of a bad fuel pump is possible.
 
I have the p0301 issue and will be changing out the valve springs after checking that the rockers are all still there and pushing the rods correctly. Fuel pump alone will not cause a 301 error, unless the pump is pushing out debris and the one injector caught all of it.

Suggestion about to take out the rail and inspect is not a bad one. Swap out the injectors after marking them to see if the error moves up the chain or stays the same.

Was the head re-used? Any parts from the old motor re-used at all?
 
On
Ephry73 said:
I have the p0301 issue and will be changing out the valve springs after checking that the rockers are all still there and pushing the rods correctly. Fuel pump alone will not cause a 301 error, unless the pump is pushing out debris and the one injector caught all of it.

Suggestion about to take out the rail and inspect is not a bad one. Swap out the injectors after marking them to see if the error moves up the chain or stays the same.

Was the head re-used? Any parts from the old motor re-used at all?
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only my intake manifold was reused
 
BrunoPizz97 said:
On
only my intake manifold was reused
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I would definitely take the valve cover off and check the rockers to make sure something did not come loose while running the motor under load. make sure the pushrods are seated where they should be. Obvious and usual suspects should be checked as well, like plug gaps and torque of said plugs, correct timing order of the plug wires, cam sensor seated all the way, crankshaft sensor, etc... Things get loose and it becomes an issue if left be. Eliminate the obvious first and go from there. In my case, it is definitely a recall valve spring issue and I have a fix for it.
 
Seemed to be my injector being clogged, good thing I had a spare one. Swapped out 1 with 4 and the problem followed, so I swapped 4 which was one with an injector that I had. Runs great no more sputter.
 
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BrunoPizz97 said:
so now its starting to sputter again, I dont know was causing my injectors to clog up. I dont see anything clogging up my injectors. Has anyone ever had an issue like this before?
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Dirty fuel? You could always try a cheap temp fix by adding an inline fuel filter somewhere before the fuel rail. Then if that solves it you can drop your tank, clean it out and replace the fuel filter (pump) inside.
 
Go to your PCM & disconnect all the connectors. Spray both the PCM contacts & the inside of the connectors with electrical cleaning spray. Wait for them to dry & reassemble. This cleared up my PO301 code 100%. Worth a try, no?
 
CodaMan said:
Dirty fuel? You could always try a cheap temp fix by adding an inline fuel filter somewhere before the fuel rail. Then if that solves it you can drop your tank, clean it out and replace the fuel filter (pump) inside.
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well im replacing the pump next week anyways so ill be blowing out my lines when its time. So hopefully it solves my issue.
 
driftless said:
Go to your PCM & disconnect all the connectors. Spray both the PCM contacts & the inside of the connectors with electrical cleaning spray. Wait for them to dry & reassemble. This cleared up my PO301 code 100%. Worth a try, no?
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definitely worth a try, Ill pick some spray on my way home and let it sit for a couple of hours. But im not getting the code anymore after the injector swap, Im getting a sputter on startup for a few seconds no doubt in my mind that on one of the startups it will trigger the P0301 code.
 
BrunoPizz97 said:
definitely worth a try, Ill pick some spray on my way home and let it sit for a couple of hours. But im not getting the code anymore after the injector swap, Im getting a sputter on startup for a few seconds no doubt in my mind that on one of the startups it will trigger the P0301 code.
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Is it still a P0301 code? You said it moved to P0304 after an injector swap.
 
CodaMan said:
Is it still a P0301 code? You said it moved to P0304 after an injector swap.
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CEL popped up when I started up to go for lunch. And yes it moved to cyl 4 when I swapped it so I put in an old injector I kept as a spare and then the problem went away. My guess now is that the injector is clogged with shit again.
 
BrunoPizz97 said:
CEL popped up when I started up to go for lunch. And yes it moved to cyl 4 when I swapped it so I put in an old injector I kept as a spare and then the problem went away. My guess now is that the injector is clogged with shit again.
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And again I didn’t have a sputter when I swapped the injector but after 2 days the sputter came back along with the CEL. But keep in mind it smooths our so I don’t feel misfires after startup.
 
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.
 
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