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  #1  
Old 05-04-2015, 09:44 PM
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Running a little rough

Hello fellas

So now my moms jeep is acting up. Its a 04 WJ with a 4.0 I6. Has around 160k on it. Its running rough. By that I mean is shakes kinda hard around 1500 give or take a few hundred. The codes that came off were O2 sensor which was there before and didn't bother it much. Another code that concerns me the first time we pulled the codes, one was cylinder 3 misfire, but after resetting it no longer showed up. We cleaned the map sensor and it seems have made smoother around the idle rpm but it still running rough. Any suggestions? Please help!!



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  #2  
Old 05-04-2015, 10:04 PM
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Re: Running a little rough

Did you check the plugs and air filter?
Which O2 sensor code you have? A bad O2 sensor can make it run too lean and finally cause misfires if the mixture becomes too lean to burn.
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  #3  
Old 05-04-2015, 11:15 PM
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Re: Running a little rough

Bank 1 sensor 2 was the one on all the readings we took
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Old 05-05-2015, 06:31 AM
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Re: Running a little rough

Ah, ok, the after cat sensor. Should not influence the fuel injection then. Did you check the plugs?
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  #5  
Old 05-05-2015, 12:02 PM
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Re: Running a little rough

/No not yet. Me and dad have been busy with work and school for me. Can you give me a rundown of what to check and in which order? Thanks
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  #6  
Old 05-05-2015, 01:00 PM
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Re: Running a little rough

If a tune-up was not done lately and dont know when the plugs where changed, its maybe a good idea to buy new ones. Use only the standard copper core plugs. You could just check them and clean/ gap them if not worn too far down. Also a clean air filter is a must. If that doent help, then you could run some seafoam through the brake booster line and some in the fuel tank. Eventual carbon buildup will be removed and the fuel nozzles cleaned.
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  #7  
Old 05-05-2015, 01:28 PM
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Re: Running a little rough

Would a fuel injector cleaner help?
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Old 05-05-2015, 07:57 PM
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Re: Running a little rough

You could try that, but the advantage of seafoam is that it removes carbon buildup on the cylinder head and valves.
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  #9  
Old 05-05-2015, 09:42 PM
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Re: Running a little rough

Quote:
Originally Posted by Frango100 View Post
Did you check the plugs and air filter?
Which O2 sensor code you have? A bad O2 sensor can make it run too lean and finally cause misfires if the mixture becomes too lean to burn.
Is that a Jeep thing? On other vehicles I've had if the front O2 sensor goes bad the computer is set to mixture rich to prevent a lean mixture that can lead to detonation.
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  #10  
Old 05-05-2015, 09:56 PM
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Re: Running a little rough

Quote:
Originally Posted by JeepMe View Post
Is that a Jeep thing? On other vehicles I've had if the front O2 sensor goes bad the computer is set to mixture rich to prevent a lean mixture that can lead to detonation.
The problem is that if the PCM doesn´t see the O2 sensor as faulty, but its showing a rich mixture to the PCM, while in fact it is not. The PCM will downtrim the fuel injected, and that can go so lean that it will simply not ignite anymore and a misfire occurs.
If the PCM sees that the O2 sensor is bad, it will simply not use its reading and operate in open loop mode.
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  #11  
Old 05-06-2015, 08:38 PM
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Re: Running a little rough

Quote:
Originally Posted by Frango100 View Post
The problem is that if the PCM doesn´t see the O2 sensor as faulty, but its showing a rich mixture to the PCM, while in fact it is not. The PCM will downtrim the fuel injected, and that can go so lean that it will simply not ignite anymore and a misfire occurs.
If the PCM sees that the O2 sensor is bad, it will simply not use its reading and operate in open loop mode.
If it's throwing a code for the O2 sensor, would it be logical to assume the PCM sees the O2 sensor as faulty?
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  #12  
Old 05-06-2015, 09:34 PM
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Re: Running a little rough

Quote:
Originally Posted by JeepMe View Post
If it's throwing a code for the O2 sensor, would it be logical to assume the PCM sees the O2 sensor as faulty?
Yes, it is, because its the PCM which monitors the O2 sensor and generates the fault code.
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