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Unread 02-22-2007, 05:53 PM   #1
Grape Ape
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1992 YJ Wrangler 
Join Date: Aug 2005
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Oxygen Sensor question

I have a 92 YJ with a 4.0 automatic.

I got a check engine light code yesterday. Checked the codes and it is 21 (O2S stays at center or O2S shorted to voltage). No problem I can fix it.

The question I have is what does that cause in the engine? I have very little knowledge regarding fuel issues (IE: How a vehicle runs when lean, rich, etc...) The reason I ask what it causes is that I only drove it a little yesterday when I noticed the CEL today, I ran to the store and noticed that my jeep is quite a bit peppier. I stomp on it and she responds, much better than just the other day when I was out playing.

Is that due to something regarding the fuel and O2 sensor? Or is it something else and the O2 sensor just happened to crap out at this time?

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Unread 02-22-2007, 06:30 PM   #2
witchy woman
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The control module reads the exhaust via the O2 sensor and adjusts the mixture/fuel rate accordingly. They do wear out. I replaced one on my wife's van recently and it runs much better. Uses substantially less gas with a functioning sensor. It's just part of the whole ignition/fuel control sensor array. Your sensor may have been giving a false reading that made the engine run sluggishly.
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Unread 02-22-2007, 08:41 PM   #3
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1988 YJ Wrangler 
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If it's original it prolly wore out. The ethinol(sp?) for winter gas grades nowadays is really hard on them.
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Unread 02-22-2007, 09:30 PM   #4
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Mine crap'd out a while ago and I just got around to replacing it last weekend... It runs slightly better (no sputtering at highway speeds) and uses a bit less gas... I think I got a few extra miles out of the Heep when I filled up today...
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