How is my YJ running fine without an O2 sensor? - Jeep Wrangler Forum
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Old 09-06-2011, 05:42 PM   #1
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How is my YJ running fine without an O2 sensor?

I was underneath my YJ (93 4.0 5spd), and noticed that the O2 sensor is busted and nothing is connected to the harness. I haven't felt any drivabilty problems or hesitations at all. My old ZJ ran like crap when the o2 went so what gives? Or should I just shut up and be happy

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Old 09-06-2011, 08:34 PM   #2
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The 02 sensor only fine tunes the fuel mixture, and if the PCM loses the signal it defaults to pre mapped values that can run the engine relatively well. All fuel injected engines run this way until they are up to normal operating temp, or at least the 02 sensor(s) are warmed up. My guess is you may just happen to be in ambient air temp and pressure that suits the default operation ok, and when the season starts to change you'll notice a small change in performance. I would just change it out, it's probably affecting your fuel economy.

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Old 09-06-2011, 08:56 PM   #3
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My '90 4.2L runs great without an O2 sensor...well...the emissions tech had a different opinion...
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Old 09-07-2011, 08:57 AM   #4
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Its a yj brother,I would keep my mouth shut and not question the power that the yj holds HAHA
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Old 09-07-2011, 09:05 AM   #5
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Quote:
Originally Posted by Matcheen
My '90 4.2L runs great without an O2 sensor...well...the emissions tech had a different opinion...
I bet he did. I'm so glad I don't have to do emissions. I looked on Jeeps website last night to see what had been done to my jeep and two weeks after purchase it was in for "emissions compliance failure"
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Old 09-07-2011, 09:09 AM   #6
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The down stream won't have as much as an effect as the upstream will, except of coarse the CEL should be on
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Old 09-07-2011, 10:24 AM   #7
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Originally Posted by kjeeper10 View Post
The down stream won't have as much as an effect as the upstream will, except of coarse the CEL should be on
He has a YJ, there is no downstream O2.... You dont get that until OBD2
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Old 09-07-2011, 10:40 AM   #8
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Originally Posted by 2xs
He has a YJ, there is no downstream O2.... You dont get that until OBD2
I realize that he had a Yj so did I.
Only one O2- I did not know that... Huh
Though it had 2 also

I was lucky to have 4 with my Tj and I believe 4 now.

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Old 09-07-2011, 12:15 PM   #9
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That's just it, no CES lght, and yes the light does work lol. Gonna pick one up when funds allow I guess

fmhyj- that's what I was thinking
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Old 09-07-2011, 03:07 PM   #10
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That's just it, no CES lght, and yes the light does work lol. Gonna pick one up when funds allow I guess

fmhyj- that's what I was thinking
if its an open circuit, the computer will read switching voltage (the voltage threshold between rich and lean), and might not set a code. normally it would due to lack of activity.
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Old 09-07-2011, 03:38 PM   #11
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if its an open circuit, the computer will read switching voltage (the voltage threshold between rich and lean), and might not set a code. normally it would due to lack of activity.
i had this problem in my caprice recently, the o2 sensor was there, i could visually see it, no check engine light, but when hooked up to diagnostics because it wasn't passing emissions, the o2 sensor was broke, which in my caprices case, ment the engine never thought it was warmed up, so it was dumping extra fuel in the engine still and it wasn't getting burned all the way, thus high hydrocarbons

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