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Old 09-02-2010, 06:39 PM   #1
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Need help on o2 sensor short on header... no fire at coil

I have a 97 tj 2.5l, i put an aftermarket header on it and the o2 sensor is now too close to the header. the header burned through the wires on the sensor and shorted it out on the header. The jeep will turn over but not crank. I checked the fuel, and thats not the issue. I pulled a plug wire and was getting no fire so i pulled the coil wire from the dist cap and wasnt getting any fire there. I swaped out the ASD relay and the problem is still there. Some people say that the crank sensor could cause this but i dont see how the o2 sensor would have anything to do with the cps. Is there a possibility that the problem is now in the PCM? I know that is where the o2 sensors feed, and also where the coil driver is located. Also could it be a fuse blown having something to do with the PCM? Right now all the clues are pointing in that direction... if anyone has any knowledge on the situation i would greatly appreciate it.

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Old 09-02-2010, 06:53 PM   #2
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I would cut the 02 sensor wiring back enough so to get rid of the part that melted/shorted to ground through the header, then try to start it. The engine doesn't require the 02 sensor be working or even plugged in to start.

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Old 09-02-2010, 08:37 PM   #3
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yea i actually forgot to mention that i already replaced the oxygen sensor. I actually just came in from trying a new crank sensor too. Same problem still exists... it will turn over but will not fire, and there is no fire to the coil. Anymore info is greatly appreciated.
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Old 09-02-2010, 10:01 PM   #4
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When the wire shorted to ground it put too much of a load on the O2 Sensor's heater supply wire. The PCM most likely detected that it was shorted and internally shut reference power off. It's a self protection move by the PCM.

Check ALL the fuses, both under the dash and under the hood in the fuse/relay box.

If still no good, try deep cleaning the PCM memory - disconnect a battery cable OVERNIGHT at least 8 hours. The memory that it was shorted should erase, letting it get back to normal.

8 HOURS! There are lots of schemes or shortcuts that claim to do it, but they will NOT do what's needed to clear ALL the PCM memory.

Let us know.
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