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Unread 01-24-2015, 10:05 PM   #1
2001XJMuddin
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2001 XJ Cherokee 
 
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P0303 Misfire code

I have a 2001 XJ Cherokee that has a mysterious p0303 code. When this code sets my CEL will flash and I lose power due to this cylinder 3 misfire. I also have a loud tapping on cold start up and one after My oil pressure reaches 40psi... The strange thing about this is that when this happens all I have to do is kill the engine for like 2 mins and it starts back up no problem..No misfire at all. This happens about once month. I know it probably needs lifters. Im just wondering if its collapsing at times on cylinder 3 and causing this issue?

Anyone know if this problem?

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Unread 01-25-2015, 08:44 AM   #2
Kalali
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You have two separate issues. Single cylinder misfires can be caused by multitude of reasons and can only be resolved by ruling out potential causes one at a time. Do a search on single cylinder misfires and read the relevant threads. The tapping noise might be a little easier to diagnose. While you're at it, read up on the 0331 cylinder head cracks prevalent in 00-01 XJs. Just out of curiosity, what brand oil filter are you using? If the answer is FRAM, replace it with another brand like NAPA or Mopar and report back on the tapping noise or lack thereof.
Keep us posted.
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Unread 02-04-2015, 03:05 PM   #3
2001XJMuddin
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Thanks for the reply.. I had noticed that after I had got this jeep that it has an older jeep head on it because the 2001 Jeep has holes threaded for the ignition coil. I am thinking it has either a lifter or injector issue on cylinder 3? I use a mopar filter and use Lucas oil stabilizer every oil change.. Any suggestions?
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Unread 02-05-2015, 09:24 AM   #4
axlaxl
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Initial guess would be either the 0331 cylinder head crack or the #3 fuel injector heat soak issue. If the issue happens after a lot of start and stops like running errands on the weekend, etc then I'd say the heat soak issue but that is pure conjecture.

Can you get a compression and leak down test done on the #3 cylinder?
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Unread 02-05-2015, 05:14 PM   #5
tjwalker
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1. Does the flashing CEL only occur upon starting up a warm/hot engine? If so, heatsoak is in play as a suspect.

2. Are you using / having to add any anti-freeze to your coolant reservoir? The #1 symptom of a cracked 0331 cylinder head is "unexplained coolant loss". A cracked 0331 head can affect cylinder 3.
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Unread 02-06-2015, 08:20 AM   #6
axlaxl
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Quote:
Originally Posted by tjwalker View Post
1. Does the flashing CEL only occur upon starting up a warm/hot engine? If so, heatsoak is in play as a suspect.

2. Are you using / having to add any anti-freeze to your coolant reservoir? The #1 symptom of a cracked 0331 cylinder head is "unexplained coolant loss". A cracked 0331 head can affect cylinder 3.
+1 on this as both happened to my 00.

First is fairly easy to fix with some heat insulation and a zip ties.

Second, well, not so much fun to fix.
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Unread 02-10-2015, 08:53 AM   #7
2001XJMuddin
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yes, this happens only after the jeep is at operating temperature and after its started and stopped a few times. I have no overheating issues and no coolant loss at all. I have heard of this heatsoak issue as well. I was wondering if its a good idea to do the 4 hole injector upgrade and if this will help with the heatsoak issue? Any suggestions??
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Unread 02-10-2015, 11:15 AM   #8
ctm
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also look for harness rubbing against metal bracket near rear of valve cover...bracket can wear through insulation and intermittently contact wire(s) and short out injector(s)
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Unread 02-10-2015, 11:40 AM   #9
axlaxl
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Quote:
Originally Posted by 2001XJMuddin View Post
yes, this happens only after the jeep is at operating temperature and after its started and stopped a few times. I have no overheating issues and no coolant loss at all. I have heard of this heatsoak issue as well. I was wondering if its a good idea to do the 4 hole injector upgrade and if this will help with the heatsoak issue? Any suggestions??
Not sure how much it would help to upgrade to 4 hole injectors regarding this specific issue. I did the upgrade recently (along with better heat insulation on the #3 injector) and have yet to see the code again, but it is also winter, so heat soak is less of an issue.

The injector upgrade is fairly easy and not overly expensive and if you are in the 100k miles + club then it might be worth doing both at the same time just to kill 2 birds with one stone.
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