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post #1 of 7 Old 12-05-2013, 12:53 AM Thread Starter
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1999 XJ Cherokee 
Join Date: Nov 2011
Location: Karns city
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Engine Problems

hello bought a new Cherokee couple weeks ago with a stalling issue needed a vehicle bad so I picked it up and now im at a loss..... the Jeep -> 2000 Xj 4.0L Auto NP231 D30/C8.25 California exhaust (I Live in PA with no emissions test only visual inspection of Cat.) the symptoms -> Its got a Rough Idle and occasionally a bad vibration of the whole jeep it almost is Chugging 1000-2800rpm usually runs pretty good like a jeep should 2800+ RPMs it starts cutting out chugging the whole jeep with all (engine) power loss (seemed like when the jeep was under a load or pushing the engine would cause it) this is when the Check Engine Light Comes on (if its not all ready) and will start flashing......... also the exhaust was chugging after experiencing this .................. However all of this will not happen always it was running all good except for the idle

the previous owner told me (take it with a grain of salt) that he's replaced the Computer, Crank Pos. Sensor, Plugs and Coil Pack

what Ive done after some reading on here and other forums I decided to swap out my Clean throttle body off my other Cherokee and swap it with mine No change eliminating the possibility of it being the TPS, MAP, or the Idler control valve I also thought part of the problem to be cheap fuel and carbon build up so I've been running 91 octane w/ Lucas Fuel injector Cleaner through it. Also Seafoam'd it twice the first time it seemed to make a difference (not immediately) for the better everything was gone except for the idle but even that was better the second time caused it to act up this is when we noticed it making a strange sound from the exhaust and we felt the exhaust chugging

I also got advance to put it on the computer and it was reading a miss fire on #5

Im thinking Its a bad Cat and thinking about eliminating the pre cats and dealing with the check engine light because if other 4.0's can get away with one cat. so can I also dealing with the Heat Soak issue in the process since im going to wheel it in the future


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post #2 of 7 Old 12-05-2013, 12:26 PM
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2000 XJ Cherokee 
Join Date: Apr 2002
Location: out in the garage - Minneapolis
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What brand and type spark plugs ? ( Yes they can make a difference). Are the replacement parts genuine Jeep ? (Yes they can make a difference).

Have you tested the O2 sensors and inspected their fuses ? Is a misfire on #5 the only trouble code present ?

Cat Converters are there for reason, and should maintained and replaced as needed.

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post #3 of 7 Old 12-05-2013, 12:35 PM
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1992 XJ Cherokee 
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Also the Tps will definitely cause these same issues. And cj is right on too.
Have you tried pulling codes

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post #4 of 7 Old 12-06-2013, 11:30 PM Thread Starter
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1999 XJ Cherokee 
Join Date: Nov 2011
Location: Karns city
Posts: 24
I believe the emissions was tripped as well and I have not had a chance to check the plugs and like I said the tps idle control valve and the map sensor all came off a known working 110% Cherokee so it can't be the issue
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post #5 of 7 Old 12-07-2013, 04:16 AM
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1999 TJ Wrangler 
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If you had a known working XJ, why did you buy this one?

I agree with Tim, change the plugs. A CEL for a cylinder misfire doesn't mean a bad cat. Also I wouldnt just cut off the minicats, they have O2s that go with them and then you'll be all screwed up.

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post #6 of 7 Old 12-07-2013, 08:35 PM Thread Starter
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1999 XJ Cherokee 
Join Date: Nov 2011
Location: Karns city
Posts: 24
I rolled it over or I wouldn't have this POS and I just got a fuel pressure tester and sparkplugs neither of which were the issues I did get the precise codes however PO455 Vacuum Leak PO305 cylinder 5 Misfire oh and the spark plugs were basic Autolites and I replaced them with NGK's Vpowers
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post #7 of 7 Old 12-07-2013, 09:40 PM
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1985 CJ7 
Join Date: Oct 2013
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Step #1: Find that vacuum leak! A vacuum leak can destroy an engine, and the symptoms you describe could all be related to a vacuum leak (as the computer tries to adjust for it). Even the cylinder 5 misfire could be a vacuum leak.

Check the cap for cracks or carbon tracing on the inside. Check cylinder #5 plug wire resistance.

Seems the best plugs for the Jeep sixes are Champion copper plugs. V-powers won't hurt anything though.
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