3 O2 sensors????
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Junior User
Joined: Oct 2004
Posts: 51
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From: Maine
3 O2 sensors????
i have the check engine light on in my 96 XLT 302. just had a tune-up. looking on the board and noticed that 96's have 3 O2 sensors. just wante to make sure before i buy too many.
Junior User
Joined: Nov 2004
Posts: 60
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From: Texas
why does it matter to only replace one? If they are still putting out a good pattern, why replace? If it ain't broke don't fix it, is what I say. I'm open though if Kem can enlighten me on why you should replace a good sensor.
Hotshot
Joined: Jul 2002
Posts: 14,285
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From: Bend,OR
those sensors work together to provide data to the ecu. if you throw a new on in there the others will begin to fail as well. ive seen it to many times. If you had one bad spark plug would you just replace it or all of them. i would think all of them .
o2 sensors are finicky, if one is new it will recieve a better reading then the others and compensate for this which may cause the otherside to go lean or rich
o2 sensors are finicky, if one is new it will recieve a better reading then the others and compensate for this which may cause the otherside to go lean or rich
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Junior User
Joined: Nov 2004
Posts: 60
Likes: 0
From: Texas
Definitely replace all spark plugs, although 02 sensors aren't quite the same, but I do see your point. I have never had that problem, but if you have . . . I do know they break down over time.
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Elder User
Joined: Dec 2002
Posts: 559
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From: South Carolina
O2 sensors do wear out and become less efficient over time. On OBD I (pre 1996) vehicles, it's a sound idea to replace the single sensor at 60-70 thousand miles. On OBD II (1996 and beyond) vehicles, the tolerances for low emissions are much tighter - the computer will set a code for poor performance long before the owner will likely notice a decrease in performance. The individual sensors are usually at least twice as expensive as the OBD I counterparts. The OBD II ECM is the best indicator of worn parts - when tolerances decrease, it will let you know. If you're inclined to, replacing three sensors sure won't hurt anything - but why do it when the ECM will continually test them for you?
Junior User
Joined: Jan 2001
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Ford OBD-II computers run the O2 heater circuits to the PCM and can immediately detect if the heater circuit fails. But the PCM is not nearly as good at detecting an aging sensor.
The downstream sensor is used to monitor the cat efficiency and has no effect on the air/fuel mixture. The closed loop mixture control is accomplished by the upstream sensors.
My two cents...
John
The downstream sensor is used to monitor the cat efficiency and has no effect on the air/fuel mixture. The closed loop mixture control is accomplished by the upstream sensors.
My two cents...
John
Elder User
Joined: Dec 2002
Posts: 559
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From: South Carolina
Well, it looks like we're all sorta right. Here's a good article on O2 Sensor function and recommended replacement periods.
http://www.babcox.com/editorial/ic/ic10044.htm
http://www.babcox.com/editorial/ic/ic10044.htm