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Of course after 6 years of trying to slove a misfire it was the O2 sensor.

Old 03-15-2019, 07:47 PM
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Location: syracuse ny
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Year: 1997
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Engine: 4.0
Unhappy Of course after 6 years of trying to solve a misfire, it was the O2 sensor.

Yeah, I know I am stupid now. So on a whim, actually a very well educated guess, I unplugged the front o2 sensor to see if it would cure my cold misfire and stumble which were quite pronounced. What the heck...a full on valve job didn't do it. New injectors didn't cure it. Nor did every other sensor and controller, new dizzy, alt, batt, fuel pump, etc etc etc. so by process of elimination, there was nothing left to suspect but the PCM or the O2 sensor. I unplugged the O2 sensor this morning as the weather went above 50 for the first time in 45 days. Whadda ya think. Immediately started and ran smooth. Drove it all day and like a different engine. Smooth, less pedal. A dream compared to what it was. Yes, it set the O2 sensor voltage high code. No, so far the O2 heater monitor did not set, which puzzles me a bit. It doesn't set soon Ill start to think the PCM is bad. It's already bad because the alternator won't charge well when the loads are on.
So now I ordered a new NTK for it. However..I worry that the front pipe will break when the old one comes out.
Anyone ever remove one from a 200k front pipe?

Last edited by 97grand4.0; 03-16-2019 at 04:58 AM. Reason: sp.
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Old 03-16-2019, 05:56 AM
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Suppose now it could also be something like a vacuum leak. There is the matter of the 1 evap monitor that won't run. I had done all the tests to the sensor with a graphing scanner, looked good except maybe only went to .8 volts instead of .9, Added propane and created vacuum leak and the sensor immediately changed..not real definitive. Also the matter of the sensor heater monitor that looks fine even with the sensor unplugged.

Last edited by 97grand4.0; 03-16-2019 at 05:58 AM.
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