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  #1  
Old July 25th, 2020, 10:00
MVU2ORC MVU2ORC is offline
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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
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Old July 25th, 2020, 10:07
MVU2ORC MVU2ORC is offline
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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  
Old July 25th, 2020, 11:28
RCP Phx RCP Phx is online now
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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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Old July 25th, 2020, 12:11
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Tim_MN Tim_MN is offline
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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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Originally Posted by bimmerjeeper

People are dumbfounded when I tell them I know how to change the spark plugs on a car.
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  #5  
Old July 25th, 2020, 12:59
MVU2ORC MVU2ORC is offline
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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  
Old July 25th, 2020, 13:02
MVU2ORC MVU2ORC is offline
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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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Old July 25th, 2020, 14:07
RCP Phx RCP Phx is online now
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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
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  #8  
Old July 25th, 2020, 14:16
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Tim_MN Tim_MN is offline
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Re: Need help with mis at idle

Quote:
Originally Posted by MVU2ORC View Post
...... Not sure I under stand the second part referring to the genuine jeep obd engine sensor
Most auto parts stores sell cheap crappy Chinese made parts, some that even come with a "Lifetime Warranty". These parts are poorly manufactured and/or made from inferior materials. They are often out of specification, or even failed, right out of the box. The ones that are not faulty many times will have a short service life before they fail. Always buy top quality replacement parts and genuine Jeep engine sensors.

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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Quote:
Originally Posted by bimmerjeeper

People are dumbfounded when I tell them I know how to change the spark plugs on a car.
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  #9  
Old July 25th, 2020, 14:24
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

Quote:
Originally Posted by RCP Phx View Post
A little long, but skip to post #39 for the start of the details!
https://naxja.org/forum/showthread.php?t=1145993
I will take a look! thank you!
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  #10  
Old July 25th, 2020, 18:50
Agreen Agreen is offline
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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?
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  #11  
Old July 26th, 2020, 05:05
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

Quote:
Originally Posted by Agreen View Post
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?
Yes I put them in and the idle mIS did not change but I did start getting mis fire codes. Put the new ones back in and no more codes

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
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  #12  
Old July 26th, 2020, 05:11
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

Quote:
Originally Posted by RCP Phx View Post
A little long, but skip to post #39 for the start of the details!
https://naxja.org/forum/showthread.php?t=1145993
Dove into the harness it does look pretty bad. Most of the damage fraying seems to be the bundle of wires That take off between cylinder 5/6 serving the map sensor, TPS, idle control sensor.
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  #13  
Old July 26th, 2020, 07:18
CJR CJR is offline
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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
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Old July 26th, 2020, 08:10
MVU2ORC MVU2ORC is offline
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Re: Need help with mis at idle

Quote:
Originally Posted by CJR View Post
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
The engine has a rough idle. Bounces around 675- 725 rpm. Sitting in the drivers seat you can feel the car shake. It is fairly consistent. Would spraying started fluid around the intake manifold work to detect leaks or are suggesting a purely visual inspection?
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  #15  
Old July 26th, 2020, 08:14
RCP Phx RCP Phx is online now
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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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