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Misfires on all cylindes, poor performance, poor mileage, hesitation, and backfires.

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Misfires on all cylindes, poor performance, poor mileage, hesitation, and backfires.

Old 10-12-2012, 02:10 AM
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Default Misfires on all cylindes, poor performance, poor mileage, hesitation, and backfires.

I'm having some issues that recently became serious.

I drive a '98 2 Door XJ 4x4 w/ the 4.0, 5-speed.

What's brought me to finally posting has been a pending random/multiple misfire code, and after work today in the parking lot, I brought the RPMs to around 3k for about 30secs(read something on another forum...) and then threw a CEL and Torque read actual P0300 Random/Multiple Misfire, and then codes for all cylinders misfiring. I cleared the codes, and made the ~30mi drive home, but I was noticeably lacking power and Torque's MPG estimate was ~14MPG.

Recently It's been harder(longer) to start cold, mileage has been getting worse and worse. Performance has been poor too, just passing on the highway is difficult, and acceleration slow, sometimes backfiring or hesitating(usually when cold) Idle isn't "rough" but it's very unsteady, Torque reads roughly 720-800RPM at idle, warm. Recently replaced the cat since it had stuff rattling around in it after only about 130k miles or so, and I'm fairly certain I do have a cracked exhaust manifold, but talking to my dad, an old air force mechanic, he says the manifold shouldn't have anything to do w/ this issue in particular.

Replaced the crankshaft position sensor a year or so ago, replaced plugs, wires, dist cap, and dist rotor a few months after the CKS.

So far I'm reading everything from Cam Shaft position sensor, bad dist, bad o2 sensor, bad fuel pump, etc.

This is a daily driver and I drive 50-60 miles a day mostly highway. Where I'm at gas is nearing $5/gal, so atop the fact I need reliable personal transportation, I really need to get my mileage back up to the 19-21MPG I once had.

edit: also recently replaced the TPS, MAP sensor, and IACV. Did that shortly before replacing the cat.

Last edited by DesertRat810; 10-12-2012 at 02:37 AM.
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Old 10-12-2012, 02:26 AM
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Originally Posted by DesertRat810 View Post
I'm having some issues that recently became serious.

I drive a '98 2 Door XJ 4x4 w/ the 4.0, 5-speed.

What's brought me to finally posting has been a pending random/multiple misfire code, and after work today in the parking lot, I brought the RPMs to around 3k for about 30secs(read something on another forum...) and then threw a CEL and Torque read actual P0430 Random/Multiple Misfire, and then codes for all cylinders misfiring. I cleared the codes, and made the ~30mi drive home, but I was noticeably lacking power and Torque's MPG estimate was ~14MPG.

Recently It's been harder(longer) to start cold, mileage has been getting worse and worse. Performance has been poor too, just passing on the highway is difficult, and acceleration slow, sometimes backfiring or hesitating(usually when cold) Idle isn't "rough" but it's very unsteady, Torque reads roughly 720-800RPM at idle, warm. Recently replaced the cat since it had stuff rattling around in it after only about 130k miles or so, and I'm fairly certain I do have a cracked exhaust manifold, but talking to my dad, an old air force mechanic, he says the manifold shouldn't have anything to do w/ this issue in particular.

Replaced the crankshaft position sensor a year or so ago, replaced plugs, wires, dist cap, and dist rotor a few months after the CKS.

So far I'm reading everything from Cam Shaft position sensor, bad dist, bad o2 sensor, bad fuel pump, etc.

This is a daily driver and I drive 50-60 miles a day mostly highway. Where I'm at gas is nearing $5/gal, so atop the fact I need reliable personal transportation, I really need to get my mileage back up to the 19-21MPG I once had.
you have a distributor so I assume you have a single coil set up.... check that coil, its the one thing besides the distributor that is inline with all six cylinders... if that is ok then check distributor itself. play in distributor shaft could be a problem for you too. good luck
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Old 10-12-2012, 02:39 AM
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Originally Posted by squirrelnw View Post
you have a distributor so I assume you have a single coil set up.... check that coil, its the one thing besides the distributor that is inline with all six cylinders... if that is ok then check distributor itself. play in distributor shaft could be a problem for you too. good luck

Also forgot to mention I replaced the coil when I replaced the crankshaft position sensor. Didn't know about the common CPS issue at that time, wasn't getting spark, and the old one just so happened to have a crack in it too. I will check the distributor tho, was on my list to look at. The apt. complex I'm in severely looks down upon anyone doing ANY sort of work on their own car, so this is gonna be interesting.

Last edited by DesertRat810; 10-12-2012 at 02:48 AM.
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Old 10-12-2012, 02:50 AM
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Not likely to be the problem with your 1998, but I chased a misfire for 2-years before finding it was the wiring harness.
See this thread: https://www.cherokeeforum.com/f2/new...re-help-32066/
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Old 10-12-2012, 02:54 AM
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Originally Posted by MtnHermit View Post
Not likely to be the problem with your 1998, but I chased a misfire for 2-years before finding it was the wiring harness.
See this thread: https://www.cherokeeforum.com/f2/new...re-help-32066/
Aye, fairly certain it's not my issue since it's all 6 cyl misfiring, but I love learning about peoples problems and solutions with Jeeps. Thanks for the input.

It's ~40f outside(living in CA for ~5 years makes you a wimp when it comes to temperature), almost 1am, and I work tomorrow. If I remember to I'll get out the door early and check the dist. May also reset the ECU before leaving tomorrow to. If it's a sensor issue, I'd imagine resetting the ECU will dramatically change things, at least temporarily, but if it's a physical or mechanical issue, it should remain roughly the same, no?


edit:
This gentleman has/had a VERY similar issue, but I don't see anything about him resolving it:
https://www.cherokeeforum.com/f5/mis...ot-bad-120603/

Last edited by DesertRat810; 10-12-2012 at 03:02 AM.
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Old 10-12-2012, 05:11 AM
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What you're describing can be caused by the crack in the exhaust manifold, it fits quite nicely actually. The crack lets exhaust out/air in which screws up the O2 sensor... and if you had to replace the stock cat I'm betting the pre-cat O2 sensor is on its way out. They can go bad without throwing a code, btw.
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Old 10-12-2012, 05:44 AM
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remove distributor cover for 10-20 min., it can have moisture.
If spark plug wires are bad, sometimes you can hear spark and see it at night.

Last edited by Rockville; 10-12-2012 at 05:47 AM.
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Old 10-13-2012, 02:39 PM
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Resetting ECU helped, didn't fix, but helped. Also, I've noticed 5th gear is pretty much useless, and get better mileage going down the highway in 4th. Amusingly, the other night I decided to flow w/ the "very fast" traffic of about 2 or 3 other vehicles and performance and mileage was much better at higher RPMs and higher speeds(80-95MPH). Oh Jeeps...

Since I can't really work on my Jeep myself where I'm at too much, what should I expect to pay a mechanic to put a new exhaust manifold on if I supply the manifold and gasket(s)?

Originally Posted by Rockville View Post
remove distributor cover for 10-20 min., it can have moisture.
If spark plug wires are bad, sometimes you can hear spark and see it at night.
Will check for arcing between wires at night. The wires are pretty new. Bosch set. The routing that's default in the engine compartment always worries me since they're so close to eachother, overlapping in some places, and making very tight bends in others. Suppose they may have gone bad in a lil over a yr.

Last edited by DesertRat810; 10-13-2012 at 02:42 PM.
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