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Old 03-04-2013, 07:09 PM   #1
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Oxygen sensor

I've connected Jeep on diagnostic tool.. o2 sensor readings are between 0.3v and 0.8v constantly varying on hot idle. Seems like it gets to 0.5v and then get to 0.8 and later to 0.2 and then again and again, like it's constantly needing more fuel in mixture and corrections are within 10%

Would a crack in exhaust manifold cause false 02 readings? I've noticed that fuel consumption is some 10 mpg in town which on completely stock 4.0 is a bit high. O2 was recently replaced but no change in consumption.

There is something else like memory adaptive factor or something similar which is -75%??

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Old 03-05-2013, 07:45 AM   #2
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Anything is possible but I think for the most part regarding YJ's, the O2 sensors are supposed to be replaced at or about 88,500 miles.

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Old 03-05-2013, 10:52 AM   #3
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Yes, a leak in the exhaust manifold upstream of the O2 sensor changes the exhaust/air-ratio, and the O2 sensor will be relaying incorrect information back to the ECC.

When you replaced the sensor, did you reset the ECC? The ECC has to "re-learn" the system when you swap out sensors with new ones, otherwise it will act like the old one is still installed.

You can reset by either disconnecting the battery completely and leaving it sit overnight, or, disconnecting the battery and touching the positive terminal cable to the negative terminal cable. Both ways will drain the capacitors in the system and your ECC will attempt to relearn the system within the first 50 startups.

I had to do this several times when I replaced the TPS, IAC, O2, and CPS to correct an idling problem I had back last Summer.
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Old 03-07-2013, 02:05 PM   #4
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Thanks a lot done it , will see if there are any improvements
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