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P0301 not fixed after 1 month at dealership

2002TJ

New Member
Feb 25, 2019
3
maryland
I have a 2002 TJ with 153,000 miles on it.
Full tune up in winter 2017.
One month ago the jeep was running so rough and multiple codes came up: P0320, P0300, P0301, P0306.
I took the jeep to a local mechanic - he was unable to diagnose and suggested the jeep dealer. The jeep was at the dealer for 1 month.
Fixes included ignition coil, crank sensor, all of the plugs replaced, injectors switched around and cleaned, replaced the injector O rings, checked gas tank and fuel pump and filter. Ran the jeep for long drives and the P0301 misfire code continues to come on -missing slightly they say. They have had 5 techs and a foreman review it and are stumped. They said that everything checks out fine and perhaps its an engine internal error. I have it home now and the light just came back on.

What else can I check that the certified mechanics could miss? Bad, loose, cracked fuel cap? Bad battery? Suggestions please! I have spent hours and hours trying to figure this out.
Thank you!
 

twistedlv

TJ Enthusiast
Supporting Member
May 26, 2018
281
Las Vegas
I have a 2002 TJ with 153,000 miles on it.
Full tune up in winter 2017.
One month ago the jeep was running so rough and multiple codes came up: P0320, P0300, P0301, P0306.
I took the jeep to a local mechanic - he was unable to diagnose and suggested the jeep dealer. The jeep was at the dealer for 1 month.
Fixes included ignition coil, crank sensor, all of the plugs replaced, injectors switched around and cleaned, replaced the injector O rings, checked gas tank and fuel pump and filter. Ran the jeep for long drives and the P0301 misfire code continues to come on -missing slightly they say. They have had 5 techs and a foreman review it and are stumped. They said that everything checks out fine and perhaps its an engine internal error. I have it home now and the light just came back on.

What else can I check that the certified mechanics could miss? Bad, loose, cracked fuel cap? Bad battery? Suggestions please! I have spent hours and hours trying to figure this out.
Thank you!
Anything that affects crankshaft speed can cause a misfire dtc. Could be something as simple as a vacuum leak. Is the P0301 the only code you still get, and the others are cleared up?
Download your FSM here : https://wranglertjforum.com/attachments/2002-tj-service-manual-pdf.14039/

The p0320 you were getting shows the cam position sensor as possible cause.
 

twistedlv

TJ Enthusiast
Supporting Member
May 26, 2018
281
Las Vegas
Read your FSM. In mine it was in a section titled Driveability - Gas. It gives a whole troubleshooting sequence for P0300 family of dtc's. Some are as simple as a vacuum leak or a worn serpentine belt. Anything that could cause the crankshaft to rotate irregularly.
I feel your pain, as I am still trying to chase down an itermittent P0301. My next step is to fab up a smoke tester to check for vacuum leaks.
 
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T Crawford

TJ Enthusiast
Feb 4, 2017
326
PNW
P0301 was known as a heat soak issue on xj’s you might look into the insulation material you can put around the fuel injector
 
OP
2

2002TJ

New Member
Feb 25, 2019
3
maryland
Thank you! I will look at the FSM. I replaced the serpentine belt a few months ago and will check for a vacuum leak and look into insulation material this weekend. Losing sleep over P0301.
 

KCsTJ

TJ student
Supporting Member
Read your FSM. In mine it was in a section titled Driveability - Gas. It gives a whole troubleshooting sequence for P0300 family of dtc's. Some are as simple as a vacuum leak or a worn serpentine belt. Anything that could cause the crankshaft to rotate irregularly.
I feel your pain, as I am still trying to chase down an itermittent P0301. My next step is to fab up a smoke tester to check for vacuum leaks.
I have a pic of a smoke tester on my 97 members rides thread. Less than 10 bucks, worked great on my 2.5 and 4.0.
 

KCsTJ

TJ student
Supporting Member
@2002TJ most misfires are electrical in nature as opposed to fuel for example.

I just finished hunting down 2 different misfires, cyls 3 & 4, over a several month period on my 97 tj.

Point is, on a misfire, this could be a process as opposed to a 1 day fix.

If P301 is your only code, consider every part from the #1 spark plug all the way up the line thru the fuel injector connector all the way to the PCM could be suspect.
Check, replace 1 thing at a time and do the step by step dance till u get her done
 
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