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Unread 01-31-2013, 06:33 AM   #1
YJ-dimi
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1994 YJ Wrangler 
 
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O2 sensor should or should not be connected to ??

Hi,
can anybody help me with solving next question:My engine should or sholdn't have an O2 sensor fitted?
My wrangler has a 1994 4.0HO engine which was ran on leaded gas in the past. today it's converted to unleaded gas by cilinderhead change. The O2 sensor hasn't been present since i bought it. It runs rich (by smell and gasmileage ). The PCM doesn't send any error code on behalf of the O2 sensor so i really can't say if connecting an O2 sensor would make the PCM work with it. the O2 connector is present nearby the exhaust manifold plug but has a seal pressed in the wire-leads. I'm looking into a LPG sequantiel injection conversion kit but for avoiding lean-mixtures with gas i'd preffer a PCM working with the O2 sensor that adjusts the fuelmixture.

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Unread 01-31-2013, 07:02 AM   #2
Que89YJ
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1989 YJ Wrangler 
 
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Put one in. Yes it came stock with an O2 sensor. Yes it will run rich. OBD I diagnostics dont always come on when it has codes but this is how to check:
http://www.jeepforum.com/forum/f12/h...codes-1257145/
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Unread 01-31-2013, 07:05 AM   #3
pete1991YJ
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Yes all YJ models have an O2 sensor. It will run very rich without it, giving poor gas mileage and poor performance. Leaks at the manifld will cause the same troubles. The computer should have stored a fault code without the sensor. Also, the computer does not read the sensors until the engine temperature is above 185 deg fahrenheit. It runs in "open loop" mode until then. Hope this helps!
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Unread 01-31-2013, 07:34 AM   #4
YJ-dimi
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Quote:
Originally Posted by Que89YJ View Post
Put one in. Yes it came stock with an O2 sensor. Yes it will run rich. OBD I diagnostics dont always come on when it has codes but this is how to check:
http://www.jeepforum.com/forum/f12/h...codes-1257145/
i check codes every year when changing oil(5 in total) never had a O2 sensor related code. the only code I recall is the 55code (end of code output) that's why i'm comfused about the O2 sensor. Never measured for voltage on the wiring though maybe i'll start with that. i geuss no use for O2 sensor no use for voltage on the connector.
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Unread 01-31-2013, 07:40 AM   #5
YJ-dimi
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Quote:
Originally Posted by pete1991YJ View Post
Yes all YJ models have an O2 sensor. It will run very rich without it, giving poor gas mileage and poor performance. Leaks at the manifld will cause the same troubles. The computer should have stored a fault code without the sensor. Also, the computer does not read the sensors until the engine temperature is above 185 deg fahrenheit. It runs in "open loop" mode until then. Hope this helps!
gives nice explosions in the exhaust when going of gas and back on but but is there's no faultcode stored because of the missing O2 sensor last 5 years. when i find voltage on te connector i'll put one in and see what happens. is there any way to check if the PCM works with the O2 sensor when it's plugged in?
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Unread 01-31-2013, 08:33 AM   #6
Que89YJ
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You will know the difference. If you bought the right obd I reader for the YJ you could look at the actual numbers from the ecu. I dont know what one to recommend but I am sure you could find one with a little research. The difference in your fuel economy will be apparent after you do the change. Make sure you do a battery reset to reset the ecu. You said you checked codes. You should always see 12,33, and 55. If you dont then there is something wrong. The link I posted has the methid for checking the codes.
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Unread 02-07-2013, 11:50 PM   #7
95riorig
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Quote:
Originally Posted by Que89YJ View Post
You will know the difference. If you bought the right obd I reader for the YJ you could look at the actual numbers from the ecu. I dont know what one to recommend but I am sure you could find one with a little research. The difference in your fuel economy will be apparent after you do the change. Make sure you do a battery reset to reset the ecu. You said you checked codes. You should always see 12,33, and 55. If you dont then there is something wrong. The link I posted has the methid for checking the codes.
You should not always see 12, 33, 55

12 is only if he has disconnected the battery less than 50 engine starts.

33 is for the a/c system, if he has a/c then the code will not appear, and I believe if you don't have a/c you can unplug the a/c fuse and you won't get that code.
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Unread 02-08-2013, 03:29 AM   #8
Que89YJ
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You wil always see those codes on a stock controller unless you have changed out the ecu. The 33 is there because the ecu was set up for the xj with the ecu controlling the ac. Yj doesn't have it it has a stand alone ac. The 12 is a start of sequence.
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Unread 02-08-2013, 08:09 AM   #9
ROTTEN
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My o2 code tripped on around 100. I just black taped that light until I bought a new one.
You will notice different performance with a good o2. I can't comment yet on MPG though...
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Unread 02-08-2013, 09:37 AM   #10
Xpress
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Your engine will run worse without the O2 sensor because the computer is unable to tell what the air to fuel ratio is inside of the engine. Since it doesn't see the sensor, it runs in open loop mode, which basically means it's dumping fuel into the engine to prevent from leaning itself out to the point of destruction. You should also be experiencing poor fuel economy as well, so with the sensor in place and functioning your MPG will go up.
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Unread 03-01-2013, 07:00 AM   #11
YJ-dimi
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since my YJ is sitting throug the winter i've started the engine today and found 12Vdc on the right lead, so i'll go ahead and order a new O2 sensor.
The voltage lead is dark green/orange, if one is to look at the wiring diagram you can get at autozone.com which show the PCM and the components connected to it, you can see that from the Vdc supply dk green/orange the 12vdc goes further as black/ light blue to other engine sensors. this is kinda ood because my O2 connecter just held a dummy plug with no connections to complete the dark green/orange lead to the black/light blue wiring to supply the other engine sensors (MAP,coolant sensor/ throttle positions e.o). I'll haveto look at where that supply is comming from now(as my engine works just fine) and maybe i'll haveto cut the connection at the O2 sensor if needed to avoid shorting out when the O2 sensor makes the connection complete between the dk green/orange & black/light blu. anybody any thoughts about this?
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Unread 03-01-2013, 08:47 AM   #12
pete1991YJ
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If you have the 4-wire heated sensor then I wouldn't cut anything. At least one of those wires is supplying electricity to the heater inside the sensor.
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Unread 03-01-2013, 09:21 AM   #13
YJ-dimi
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Quote:
Originally Posted by pete1991YJ View Post
If you have the 4-wire heated sensor then I wouldn't cut anything. At least one of those wires is supplying electricity to the heater inside the sensor.
Think you're right. i've looked at the wiring again comparing with a 4wire O2 plug layout and found the wire black/light blue comming from the PCM and supplying sensors with voltage so the O2 sensor plug, i think is like this
- Dark green/orange=12Vdc coming from start ignition supplying the heating element in the O2 sensor
- black is ground from the O2 heating element
- black/light blue is voltage from PCM to O2 sensor
- black/drk green is O2 sensor voltage output to PCM, for controlling air/fuel mix.
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Unread 03-27-2013, 05:20 AM   #14
YJ-dimi
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final update,
Today i've installed the sensor. I ran the engine and it accepts the oxygen sensor. the engine ran smoother and after warming up there was increase in efficiency as the exhaust didn't gave as much expolosions as i went on/of gas. fuel-economy imprvement already . Thanks for the help.
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Unread 03-27-2013, 07:11 AM   #15
Que89YJ
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YJ-dimi did you do a battery reset? The PCM stores info and you need to clear it. Also after running rich that long you might want to clean out the IAC. I bet its carboned up pretty good.
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