P300, P301,P302,P304,P305,P306 misfire error codes - JeepForum.com
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Unread 07-05-2010, 05:51 PM   #1
aziziy
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P300, P301,P302,P304,P305,P306 misfire error codes

Hello,
I have a 2001 jeep grand Cherokee V6. It runs great and I don't have any problem with it. Yesterday the check engine light came on (while I was driving in highway) and when I check it it gave me P300, P301,P302,P304,P305,P306 misfire error codes.
I don't have any problem with my jeep though. I had changed my spark plugs last summer.
Do you have any suggestion what's going on with my jeep?
Thanks a lot in advance.
Joe

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Unread 07-05-2010, 05:54 PM   #2
aziziy
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I got 96000 miles on my jeep.
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Unread 07-05-2010, 08:46 PM   #3
kentman
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I would check the fuel pressure at the rail. Fuel pump could be going out.
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Unread 07-06-2010, 05:17 AM   #4
ratmonkey
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what plugs did you use? rechecked the gap? fuel pressure? how's the mileage been? abnormally low or high? how are your engine grounds?

btw it's an INLINE six not a V6.
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Unread 07-06-2010, 07:26 AM   #5
aziziy
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Car dealer replaced my plugs so I think it should be a platinum one. Gas mileage is normal (like it used to be). When engine is hot when I start the engine I can feel some vibration in engine which I think is misfiring. I'll check the pressure though.
Thanks
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Unread 07-06-2010, 12:13 PM   #6
jamtoy
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Crank Position Censor. Common problem and will throw those codes. Went through three on mine. Get a good one or you will be changing it again. I also found that any bad gas will do the same. Reset the pcm and all is well.

Mine also has the hot start roughness. Only does it when the air conditioning is on. Which in this heat is all the time.
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Unread 07-06-2010, 12:47 PM   #7
aziziy
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Thanks!
I reset the codes and they never came back. So I think this codes show up as I am driving in high way (60-70 mph). But in town I don't have such problem and I won't get any error code.
So it seems that something is going on while I am driving fast. I'll check PCM and fuel filter though.
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Unread 07-06-2010, 06:24 PM   #8
kentman
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The codes will probably return. I had similar issues a couple years ago on the WJ. I had to swap a few injectors for new. I think that a tank of Sunoco Ultra 94 octane in Florida started my issues.
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Unread 07-06-2010, 07:08 PM   #9
aziziy
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did you get misfire error for some cylinder or just some of them? which injector do I have to replace?
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Unread 07-06-2010, 09:45 PM   #10
kentman
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I started with 304. That moved on to 308. I think that I had 300 at one point. I replaced injectors 2, 4, and 8 if I remember correctly. It seemed like my issues were more on the passenger side of the fuel rail. Since you are getting multiple codes, it sounds more like fuel pump rather than individual injectors. Just a hunch.
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