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Unread 01-14-2012, 07:41 PM   #1
KTRJeepster
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2000 Jeep Cherokee XJ Cylinder Misfire

Hey guys new here to the Forum....I bought a 2000 XJ and the Check Engine light came on....Cyl 3 misfire!!!! So I replace the spark plugs and coil rail....nothing! While doin that I noticed antifreeze in the oil and drained 6 and a half quarts of oil....I replaced the head gasket and bought a new head and had it tested and milled....now the same thing....rough idle and skipping....since the head/head gasket fix I have tried everything suggested to fix this misfire....I wrapped the injectors with insulator shield and same thing....yesterday my girlfriend came to pick me up and the CE light was blinking the whole way....I drove home and it was real jumpy and couldn't go over 40 mph.....today the light was on and I had it checked again....Cyl 3,Cyl 6 misfires and random cyl misfire!!!! If anyone could help it would be GREATLY appreciated

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Unread 02-02-2012, 07:43 PM   #2
KTRJeepster
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Ok some help would be very nice....from ANYONE!!! Lol.... Ok since this last fiasco I have replaced the camshaft position sensor and tested and made sure that the coil pack rail was good.... Does anyone know that if the oil pressure switch is bad ( when the jeep is warmed up the oil pressure drops to 0!)....If that switch is bad will that make the vehicle shut down when the pressure drops? ANY help would be greatly appreciated..... And Thanks A LOT to anyone who does help
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Unread 02-02-2012, 10:11 PM   #3
XJnoob2012
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Got nothing for you on the oil problem. Hope that is all in the electronics or this thing is in trouble.

About that misfire...from the reading I have done, insulating the injectors alone rarely does the trick. Most folks generally agree that you need to insulate the crap out of the injectors and the entire fuel rail too. Additionally, the XJs tend to be fickle about what spark plugs you put in. Either keep the cheapo copper plugs or through in the autolite platinums... most other options are not recommended.

Recently had the 0303 misfire and random misfire issues. Finally went away after I did everything...insulation, plugs, coil rail. Not sure what else you may have going on, but it may also be a computer issue.
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Unread 02-03-2012, 04:24 AM   #4
tjwalker
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Anytime I see "random misfire P0300, I concentrate on one "common" cause for the misfires. Like weak fuel delivery or a pretty big vacuum leak. The P0300 is very likely responsible for setting the misfire codes for the other misfires on cylinders 3 and 6.

Also know that a flashing check engine light indicates a serious misfire, which if not resolved quickly, will destroy your catalytic converter. You need to resolve this immediately. If you can't figure it out, get it to a shop.

1. Verify your exact fuel pressure with a gauge. No shortcuts. Many big box parts stores will rent you a gauge inexpensively. For a 2000, you should have 49 psi, plus or minus 5 psi.

2. Perform a comprehensive search for a vacuum leak.
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Unread 02-03-2012, 07:57 AM   #5
rsurran
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What type of spark plugs are you using? My 2000 did a similar thing after replacing the NGK R plugs with another premium brand. I now use only NGK plugs, my Jeep loves them. You could be fighting a ghost.
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Unread 02-03-2012, 08:03 AM   #6
Azzy
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I get a constant misfire on 3 in the summer, or when really pushing the 01 XJ, its from a heat soak issue. Basically, the heat under the hood vaporizes the gas before it gets out of the injector, leading to some oddities in the system and a rough idle.

Almost always happens after running for a bit, stopping at a store or for gas, and then starting again.

This similar to what you have?
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Unread 02-04-2012, 08:48 AM   #7
KTRJeepster
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Ok xjnoob, thanks a lot....I never heard about insulating the fuel rail too but I'm gonna try it as well as some different spark plugs and I'm hoping that it isn't a computer issue

TJwalker.... I have an autozone nearby would they rent that gauge? And how do u test the psi's? Also where do u recommend me checking for a vacuum leak at?

Rsurran- I'm using just the cheap spark plugs.... What r NGK plugs?

Azzy- yes this is kinda the issue but I've wrapped the spark plugs with insulator tape which is what u should try doing....someone else has told me on here to also wrap the fuel rail which may also help...

TO ANYONE---- if it is a computer issue how can I get that checked? I've recently reset the ECU by removing the battery cables and touching them together for 30 seconds, then turn on the key, turn headlights on then off then turning the key off....this resets the ECU back to factory settings and allows the jeep to "relearn" ur driving habits..... I believe that my problem is probably with FUEL which leads me to think something with the injectors? Any other responses will help and thanks to u guys who have responded
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Unread 02-04-2012, 08:49 AM   #8
KTRJeepster
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Ok xjnoob, thanks a lot....I never heard about insulating the fuel rail too but I'm gonna try it as well as some different spark plugs and I'm hoping that it isn't a computer issue

TJwalker.... I have an autozone nearby would they rent that gauge? And how do u test the psi's? Also where do u recommend me checking for a vacuum leak at?

Rsurran- I'm using just the cheap spark plugs.... What r NGK plugs?

Azzy- yes this is kinda the issue but I've wrapped the spark plugs with insulator tape which is what u should try doing....someone else has told me on here to also wrap the fuel rail which may also help...

TO ANYONE---- if it is a computer issue how can I get that checked? I've recently reset the ECU by removing the battery cables and touching them together for 30 seconds, then turn on the key, turn headlights on then off then turning the key off....this resets the ECU back to factory settings and allows the jeep to "relearn" ur driving habits..... I believe that my problem is probably with FUEL which leads me to think something with the injectors? Any other responses will help and thanks to u guys who have responded
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Unread 02-04-2012, 08:52 AM   #9
rsurran
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Spark Plugs

Rsurran- I'm using just the cheap spark plugs.... What r NGK plugs?

NGK R spark plugs are copper core plugs that 2000-2001 ignition rail systems seem to like. If you are using solid copper core plugs you might be ok.
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Unread 02-04-2012, 09:10 AM   #10
Azzy
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wrapping teh spark plug wires with the insulator isnt going to do much. Its the heat that works its way up from the exhaust manifold, thought the opening in the intake, and warms up static gasoline in the injector rail, right at about injector #3. Wrap that with the insulator, or fabricate a heat shield.
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Unread 02-04-2012, 11:09 PM   #11
joe108
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KTR, I too just bought a 00 about three weeks ago and suffered exactly the misfire you described. Mine did it after offroading and shutting it down. Heat soaked the engine and the injectors. Once I got it moving and air circulating, all was fine. I'm in the process of re-doing the entire cooling system and see what happens. The other cherokees that were in the group did not suffer as mine did, but in addition to having up to snuff cooling systems, they also installed a neat(and $) cowl hood that lets hot air out the back of the hood area, neat hood.
Post any improvements on wrapping the fuel system under the hood, interested on what you come up with.
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