98 Cherokee...P0301...help!

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zrxkawboy

zrxkawboy

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I just bought a '98 Cherokee 4.0, and I'm regretting it. Engine ran a bit rough at idle when I looked at it, but figured it just needed a little TLC. Well, it has a P0301 (cyl 1 misfire) that I can't figure out. This is my first real experience with a 4.0, so I'm hoping you guys with more experience can help me out.

I have:

swapped plugs w/ cyl 2 (cyl 1 plug did look a little darker, but wasn't wet)
swapped plug wires w/ cyl 6
swapped fuel injectors w/ cyl 2
swapped fuel injector connectors w/ cyl 2
inspected cap and rotor (they look new)
checked compression in cyl 1 (130 psi)

Between each of the "swaps", I cleared the code. Then I started it, and after a few minutes of idling, P0301 would show up as a pending code.

It has 181k miles on it. Any help is much appreciated!
 
No, that is on the 00-01 models, I believe. Mine has just one coil, and a distributor.
 
call a jeep/chrysler dealer and see if there is an open recall on the vehicle for the catalytic converter and pcm update. there was a campaign that included model years 96, 97, and some 98 model year cherokees.
under this recall, fouled cats are replaced and pcm's are updated because the pcm did not recognize fuel trim and catalyst efficiency issues and set check engine lights for catalyst efficiency issues.
 
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A 98 will have a single coil. I would suggest a thorough throttle body cleaning , along with cleaning the IAC valve as well. A new set of plug wires , champion or ngk plugs and rotor cap and rotor are in order. Make sure to get rotor cap and rotor with copper connecters, BWD select line are good products. obviously change the air filter and oil , QS Defy works well in this engine. I would also suggest a fuel system cleaner such as Chevron Techron , Redline Si-1 or BG44k. The 4.0 is a very reliable engine , with a little bit of tlc you should have it running good.
 
Thanks, guys. I do have a semi-update. A co-worker had sent me a link to the public library's auto repair section, where I can read TSBs. There is a TSB about misfires, and the fix is to use Mopar Combustion Chamber Cleaner and replace the valve springs (apparently with a revised part). Hopefully the local dealer has some cleaner on hand, and I'll try it this weekend.

Keep the ideas coming...the more things to check, the sooner I'll (hopefully) find it. Thanks!
 
Originally Posted By: zrxkawboy
Thanks, guys. I do have a semi-update. A co-worker had sent me a link to the public library's auto repair section, where I can read TSBs. There is a TSB about misfires, and the fix is to use Mopar Combustion Chamber Cleaner and replace the valve springs (apparently with a revised part). Hopefully the local dealer has some cleaner on hand, and I'll try it this weekend.

Keep the ideas coming...the more things to check, the sooner I'll (hopefully) find it. Thanks!

2 bottles of techron concentrate run slowly through the brake booster as you rev rev the engine at 2500rpm will replicate the Mopar Combustion Chamber Cleaner TSB. I do that every so often to my cars as preventative maintenance.
 
Mine had a similar issue on cylinder #3. It ended up being a broken intake valve spring. When it runs rough will it pop through the intake? Pop the valve cover and take a look, it is fairly easy on these motors.
 
Didn't Eric The Car Guy do a video on exact same issue? He actually had the engine running with the valve cover off. I have to warn you though that his fix did not work and the vehicle needed a new engine.
 
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Update: I performed the Combustion Chamber Cleaning procedure, then cleared the code. It didn't come back through three different warm up/cool downs, which included about an hour of idling and driving at varying engine speeds. Then it went back to doing what it did before: P0301 as a pending code after a few minutes of running. So, the CCC made a real difference, at least for a while.

I did pull the valve cover, and found nothing broken or amiss. I had my daughter crank the engine over while I watched, and all rockers seemed to move approximately the same amount.

I think my next step is to replace the valve springs on cyl 1 per the TSB, and possibly run the CCC again. Any input is welcome. Thanks!
 
at home it is a fairly easy thing also to swap injectors and see if things change, just clean around them and slip up the fuel rail far enough to swap # 1 and 2 injector then drive again. Remember anything that makes a cylinder lower output than the other will set a missfire not just ignition. also you may want to check all cylinder comp. to make sure 130 is good with other five also and vacume leak around intake or a cylinder next to it puffing back in intake etc. can cause problems.
 
Per my first post, I swapped injectors. Also replaced the upper and lower o-rings on all injectors. Didn't mention it, but also sprayed carb cleaner around intake while engine was running to check for vacuum leak.

I could check compression on other 5, but I guess I'm not sure what good it would do, since the problem cyl meets factory specs.
 
Originally Posted By: SteveSRT8
I'd double check.


They got a very thorough check. Believe me, I was hoping I'd find one broken. But like I said, I'm probably going to replace them anyway.
 
What are different about the "new" valve-springs, compared to the originals? And why would that make a difference?
 
Originally Posted By: MarkM66
What are different about the "new" valve-springs, compared to the originals? And why would that make a difference?


Good question! The TSB gives no explanation, just says to replace all 12 and gives a part #. I'm guessing they may have more pressure, preventing carbon build-up on the valves, but that's just a guess.
 
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