P0301 code
Thread Starter
Newbie
Joined: Dec 2022
Posts: 13
Likes: 1
P0301 code
Got new plugs, wires, and cap last night and did the simple install. Problem went away for all of 15 seconds. With finals all next week and my full time job I'm gonna have to go the lame route and have this thing professionally worked on. Just dropped her off at my trusted mechanic. Fingers still crossed for nothing major.
Thanks again for the help. I'll keep you posted as soon as I hear something (Monday afternoon).
Thanks again for the help. I'll keep you posted as soon as I hear something (Monday afternoon).
CF Veteran
Joined: Nov 2010
Posts: 5,841
Likes: 117
From: In the middle of Minnesota!
Year: 1999
Model: Cherokee
Engine: 4.0
Welcome Caden,
What year is your XJ? Always start with that information on any new thread (and engine if other than the 4.0) as there are significant differences through the years of the XJ.
Hold off on that injector harness for now. For a single cylinder misfire (P0301), there are a few primary suspects. First one is spark plugs and you have already installed new ones. Second is a new distributor cap and rotor. These are maintenance items anyways so get new ones installed now. Third one unless it's the 2000-2001 which has a coil rail setup, is spark plug wires. If yours is older than 2000, be sure to purchase high quality wires as the el-cheapo wires are junk. Fourth suspect is the fuel injector itself. To help diagnose that, swap the fuel injector in the cylinder setting the code to a different cylinder and keep track as to which one you swapped to. If the code then follows to the one you swapped the injector to, you have your answer. Also be sure to inspect the wiring and connectors to the injectors.
If everything listed doesn't enlighten you, then you have to dig in a bit deeper. Internal issue should never be ruled out and a compression test is in order. The spec for the 4.0 is 120-150 psi with no more than a 30 psi variation between cylinders.
Good luck and keep us updated!
What year is your XJ? Always start with that information on any new thread (and engine if other than the 4.0) as there are significant differences through the years of the XJ.
Hold off on that injector harness for now. For a single cylinder misfire (P0301), there are a few primary suspects. First one is spark plugs and you have already installed new ones. Second is a new distributor cap and rotor. These are maintenance items anyways so get new ones installed now. Third one unless it's the 2000-2001 which has a coil rail setup, is spark plug wires. If yours is older than 2000, be sure to purchase high quality wires as the el-cheapo wires are junk. Fourth suspect is the fuel injector itself. To help diagnose that, swap the fuel injector in the cylinder setting the code to a different cylinder and keep track as to which one you swapped to. If the code then follows to the one you swapped the injector to, you have your answer. Also be sure to inspect the wiring and connectors to the injectors.
If everything listed doesn't enlighten you, then you have to dig in a bit deeper. Internal issue should never be ruled out and a compression test is in order. The spec for the 4.0 is 120-150 psi with no more than a 30 psi variation between cylinders.
Good luck and keep us updated!
Last edited by tjwalker; Dec 16, 2022 at 07:33 AM.
Thread Starter
Newbie
Joined: Dec 2022
Posts: 13
Likes: 1
Welcome Caden,
What year is your XJ? Always start with that information on any new thread (and engine if other than the 4.0) as there are significant differences through the years of the XJ.
Hold off on that injector harness for now. For a single cylinder misfire (P0301), there are a few primary suspects. First one is spark plugs and you have already installed new ones. Second is a new distributor cap and rotor. These are maintenance items anyways so get new ones installed now. Third one unless it's the 2000-2001 which has a coil rail setup, is spark plug wires. If yours is older than 2000, be sure to purchase high quality wires as the el-cheapo wires are junk. Fourth suspect is the fuel injector itself. To help diagnose that, swap the fuel injector in the cylinder setting the code to a different cylinder and keep track as to which one you swapped to. If the code then follows to the one you swapped the injector to, you have your answer. Also be sure to inspect the wiring and connectors to the injectors.
If everything listed doesn't enlighten you, then you have to dig in a bit deeper. Internal issue should never be ruled out and a compression test is in order. The spec for the 4.0 is 120-150 psi with no more than a 30 psi variation between cylinders.
Good luck and keep us updated!
What year is your XJ? Always start with that information on any new thread (and engine if other than the 4.0) as there are significant differences through the years of the XJ.
Hold off on that injector harness for now. For a single cylinder misfire (P0301), there are a few primary suspects. First one is spark plugs and you have already installed new ones. Second is a new distributor cap and rotor. These are maintenance items anyways so get new ones installed now. Third one unless it's the 2000-2001 which has a coil rail setup, is spark plug wires. If yours is older than 2000, be sure to purchase high quality wires as the el-cheapo wires are junk. Fourth suspect is the fuel injector itself. To help diagnose that, swap the fuel injector in the cylinder setting the code to a different cylinder and keep track as to which one you swapped to. If the code then follows to the one you swapped the injector to, you have your answer. Also be sure to inspect the wiring and connectors to the injectors.
If everything listed doesn't enlighten you, then you have to dig in a bit deeper. Internal issue should never be ruled out and a compression test is in order. The spec for the 4.0 is 120-150 psi with no more than a 30 psi variation between cylinders.
Good luck and keep us updated!
Junior Member
Joined: Nov 2021
Posts: 36
Likes: 1
Model: Cherokee (XJ)
My 01 4.0l threw a check engine light. Was off roading went through a stream and pulled up an incline and parked. When I restarted immediately had a check engine light. Popped the hood to observe and continued with my ride. Next day went to AutoZone to have the code read. 0301, cylinder 3 misfire. Cleared the code and haven’t seen it in 1500 mikes. Figured I got a little water onto the coil pack. I recently had a compression test and cylinder 3 was lower than the rest. Was told that’s not unusual and it is to spec.
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