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OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs. |
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#1
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Need help with mis at idle
Hello everyone. I have a 2001 xj with a rebuilt engine (approximately) 10000 mile on it. Ever since the rebuild I have had a rough idle and suffer from poor fuel economy. Here is a list of what I have checked replaced so far.
New plugs, coil pack and injectors at the time of rebuild. Cam shaft sensor synced at the dealer. New idle air controller Map Sensor 0" 4.56, 5" 3.91, 10" 3.03, 20" 1.45, 21" 1.1 Throttle position sensor was within spec at time of test but I don't remember the numbers. Compression test over 165 in all cylinders Leak down test 5% drop in cylinders 1 and 2. 2% drop in cylinders 3-6 Resistance test from PCM driver wire to pin 2 of injectors: cylinder 1 injector 0.4, 2 0.2, 3 0.2, 4 0.2, 5 0.3, 6 0.1 |
#2
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Re: Need help with mis at idle
Vacuum test feel off the initial post. 15.5-16.5 at idle. did a smoke test and got smoke out the throttle body rod. Replaced the o rings and rod, seemed to help. Also new fuel pump and and crankshaft position sensor
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#3
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Re: Need help with mis at idle
Two things to look at, first did you use Mopar parts? Second I would take a good look at your wiring harness.
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#4
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Re: Need help with mis at idle
Do you have an OBD-II scanner or APP with live data ?
What brand of O2 sensors are installed, and 2x on the genuine Jeep OBD engine sensors ?
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#5
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Re: Need help with mis at idle
I don't have a OBD II scanner, just a code reader. One shop put two scopes on it and did not find anything. I used the NTK o2 sensors, not sure on the crank sensor. Not sure I under stand the second part referring to the genuine jeep obd engine sensor
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#6
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Re: Need help with mis at idle
NTK on the o2 sensors. no on the crankshaft sensor and coil pack. Anything specific on the wiring harness? what part of the harness?
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#7
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Re: Need help with mis at idle
A little long, but skip to post #39 for the start of the details!
https://naxja.org/forum/showthread.php?t=1145993 |
#8
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Re: Need help with mis at idle
Quote:
Numerous threads detail long and frustrating searches for a "problem" that ended up being cured simply with genuine Jeep engine sensors. Cheap parts are cheap for a reason.
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#9
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Re: Need help with mis at idle
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#10
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Re: Need help with mis at idle
Is it a single cylinder misfire? To test this, unplug one injector at a time. Look for the one that doesn't seem to affect the idle as much as the others.
A good (cheap) tool to have is an ELM-327. They're about $10 on Amazon, and you can download a free app to your phone to use it. It gives you live engine data and will greatly help your troubleshooting efforts. I see that you replaced the injectors. By any chance would you happen to still have the old ones? |
#11
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Re: Need help with mis at idle
Quote:
I had what appears to be the ELM 327 but did not have luck connecting to it. Seemed to be a wifi issue as other OBD II units seem fine. I switched internet providers I will try hooking it up again |
#12
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Re: Need help with mis at idle
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#13
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Re: Need help with mis at idle
Please describe in more detail your "misfire". Likewise, I'd very carefully go over the intake manifold looking for hairline cracks, gasket air leaks, etc. Hairline cracks, in intake-manifolds, can be a PITA to detect when the cracks open and close during heat cycling.
Best regards, CJR |
#14
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Re: Need help with mis at idle
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#15
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Re: Need help with mis at idle
You definitely need to spray around the intake while warm/running.
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