Cyl 1 Misfire - P0301 ('01)

Have an '01 XJ. Just starting to get into working on my Jeep.

About three weeks ago, after driving on the freeway and shutting it off for 20 mins, it started up, idled really rough, ran rough for about a block before I shut it down and pulled it my house. A couple days later I started it up, and ran fine to local auto shop to see what the code was. It gave the P0301 Cyl 1 Misfire. Did a tune-up (spark plugs and cleaned throttle body) and ran fine for a couple weeks.

Last week, after running for 20-30 mins around town, I shut it off for 15 mins and experienced same thing as before with same code. Any ideas? Check engine comes on steady, then blinks apprx 15 times, then goes back to steady light. Thanks in advance.

Edit (based on sticky above):
4.0l
Auto transmission
'01 has ignition rail (coil over plugs).

try changing the orientation of the ignition coils and see if the code changes. for example, if you change the ignition coil from cyl 1 to cyl 3, and the code changes to P0303, then you know it's related to the coil. I know on my Mustang i had intermittent problems with a coil on plug. they were notorious for going bad, especially near the firewall where the heat builds up.
other than that, pull the fuel injector and clean the nozzle. the last time i got codes like that, the nozzle was crusted up.

Vanimal said:

try changing the orientation of the ignition coils and see if the code changes. for example, if you change the ignition coil from cyl 1 to cyl 3, and the code changes to P0303, then you know it's related to the coil. I know on my Mustang i had intermittent problems with a coil on plug. they were notorious for going bad, especially near the firewall where the heat builds up.
other than that, pull the fuel injector and clean the nozzle. the last time i got codes like that, the nozzle was crusted up.

Click to expand...

The coil pack (rail) is one peace, unable to swap cylinders (as far as I know)

However, I had this code in my 2000, It was an injector and would behave the same way. swap cyl 1 with cyl 2 injectors, if it moves its the injector. if it stays the same its not. also look for junk in the rail like a muddy/rusty buildup (mine was almost blocked) also can be causing a misfire. was a compression test done with the tune up?

gorillaxj said:

The coil pack (rail) is one peace, unable to swap cylinders (as far as I know)

However, I had this code in my 2000, It was an injector and would behave the same way. swap cyl 1 with cyl 2 injectors, if it moves its the injector. if it stays the same its not. also look for junk in the rail like a muddy/rusty buildup (mine was almost blocked) also can be causing a misfire. was a compression test done with the tune up?

Click to expand...

No compression test done at this point. Don't have the tools to do myself, but I'll check those other things you mentioned and write back.

Changed the ignition coil rail as suggested by two separate mechanics since it is one piece and you cannot test coils individually. This did not solve the problem. Will try the fuel injectors I guess.

I have a 2000 and just went through the same hassle with the #5 cylinder. R and R'd the injector and it ran great until... Seems that the wiring loom was chaffing on the back side of the fuel rail. When I changed the injector the loom was pulled away. After a few weeks it settled back on the rail. Same code. I have taped and cleared the loom and have been trouble free for a month.

Turns out when my fuel injector heated up after turning Jeep off, it would lose all resistance. Replaced injector, and o-rings. Runs great now.