P0301 cylinder misfire code. Already changed plugs to no avail. Any ideas? - JeepForum.com
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Unread 06-24-2013, 09:17 PM   #1
BobbyDash
Registered User
2004 WJ 
 
Join Date: Feb 2009
Location: Grand Rapids MI
Posts: 13
P0301 cylinder misfire code. Already changed plugs to no avail. Any ideas?

Last week I moved from Michigan to California and towed a cargo trailer the whole way with my WJ. 2600 miles and it ran pretty darn good the whole way. 14-16 hour days. So the day after it throws a P0301 code for the cylinder 1 misfire. I changed all 8 spark plugs with the recommended Champion ones. Put everything back together, no code, ran great for a day and a half and then boom, code again. Running rough. I should note that we were dumb and didn't keep track of which coil packs came from where. We just put them aside and then stuck them back in so while it's likely they ended up in different locations, it's possible coil pack 1 is back on 1 and it's the cause. (I guess, I'm no expert)

Google searches seem to suggest it could be a fuel injector? I'm not really sure where I should go from here. What tests I can run or what other things could cause it.

2004 Grand Cherokee overland 4.7HO v8

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Unread 06-24-2013, 10:29 PM   #2
99WJ539918
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1999 WJ 
 
Join Date: Aug 2008
Location: , Northern New Jersey
Posts: 1,443
Did you use Platinum plugs? Swap the coil pack from cylinder #1 to a different cylinder and see if the problem moves to that cylinder. If not, then move the injector and see if the problem moves to that cylinder. If the problem is still at cylinder #1 you can do a quick compression test. If everything still checks out you might be looking at a CKP. All in all, a pretty common problem with WJ's. Good luck.
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Unread 06-25-2013, 12:55 AM   #3
BobbyDash
Registered User
2004 WJ 
 
Join Date: Feb 2009
Location: Grand Rapids MI
Posts: 13
Quote:
Originally Posted by 99WJ539918 View Post
Did you use Platinum plugs? Swap the coil pack from cylinder #1 to a different cylinder and see if the problem moves to that cylinder. If not, then move the injector and see if the problem moves to that cylinder. If the problem is still at cylinder #1 you can do a quick compression test. If everything still checks out you might be looking at a CKP. All in all, a pretty common problem with WJ's. Good luck.

Any recommendation on how to do a compression test? I'll swap the coil packs tomorrow but yes, I believe the champion plugs are platinum. They're the ones recommended on wjjeeps
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Unread 06-25-2013, 03:34 AM   #4
99WJ539918
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1999 WJ 
 
Join Date: Aug 2008
Location: , Northern New Jersey
Posts: 1,443
You need a compression gauge and kit. You unplug the fuel pump relay, remove the spark plug in cylinder #1 (or whatever cylinder you're testing), insert the proper adapter into the spark plug hole in the head, connect the line into the compression gauge, crank the engine, and watch the gauge. Here's the one I have, but you can buy a much cheaper one:
http://buy1.snapon.com/catalog/item....re&dir=catalog
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