Still getting code 91 - MustangForums.com


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Old 11-14-2008, 10:49 PM   #1  
50GT
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Unhappy Still getting code 91

Ok guys I have replaced the O2 sensor on the left side and the code went away for about a week! The check engine light flashed again yesterday so I did the Key on engine running test and this dame code 91 popped up again! I am at a loss why the computer keeps telling me I'm running lean on the left side! Why would the left side be running lean and not the right? The last thing I have done to the car is put an off-road H-pipe but that was months ago and the code did start to appear until about three weeks ago! The code did disappear after I replaced the O2 sensor for about a week. I still have not noticed any performance problems; the car is still running strong! Please if anyone has any ideas let me know! Thanks
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Old 11-15-2008, 12:26 AM   #2  
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BTW the check engine light only flashes when the car is at a steady speed, it never flashes under hard acceleration or deceleration! Thanks
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Old 11-15-2008, 08:46 PM   #3  
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Old 11-15-2008, 09:03 PM   #4  
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I would check that you have no exhaust leaks. I had one when I installed mine and had a idle issue, then it went away after I fixed it. If i were you, i would replace the other o2 sensor.
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