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Discussion Starter · #1 ·
A bought a 91 YJ with the 4.0L straight six a few months ago. While I was crawling around doing some routine maintenance the other day, I noticed a disconnected wiring connector right underneath the oil pan. Upon further inspection, it looks like the O2 sensor is missing from the exhaust pipe.

Can anyone verify that this connector is in fact for the O2 sensor?

Also, is the sensor supposed to go into the front exhaust pipe (the 91-93 parts manual shows it going directly into the exhaust manifold, but I believe that is for the four cylinder Jeeps)?

Is there any reason why someone would have disconnected this?

Thanks in advance.
 

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yeah O2 sensor is gone only buy a NTK O2 sensor they are about $35 online and they are what the factory used and charge over $100 for from the dealer.
 

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It looks to me like the O2 sensor is broken off in the pipe? You have a cel?
 

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Should be throwing a code. Check and see if the PO pulled the check engine bulb out in the dash.

I would replace all the sensors, O2, MAP, TPS, Water Temp and Air Temp. Along with Distributer cap, plugs and wires. Or what’s been coined as a super tune up.
 

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Should be throwing a code. Check and see if the PO pulled the check engine bulb out in the dash.

I would replace all the sensors, O2, MAP, TPS, Water Temp and Air Temp. Along with Distributer cap, plugs and wires. Or what’s been coined as a super tune up.
All the above if you haven't already done so. Plus a complete fluid change. Even the brake fluid and clutch fluid. Brake fluid can absorb moisture through the years and your brakes can become spongy.

If you keep track of your maintenance, you'll have a baseline for future work.
When you do your coolant change, it'll be a good time to flush your cooling system and replace the thermostat with an OE Jeep one in the temp range that Jeep recommends.

These old heaps (or any old vehicle) require a lot more TLC than newer vehicles. By the time we get hold of them they've usually been the victim of a lot of deferred maintenance. As you go through the mentioned maintenance tasks, you might see other things that need attention, plus you'll get a better feel for your particular Jeep.

Good Luck, L.M.
 

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Discussion Starter · #6 ·
Should be throwing a code. Check and see if the PO pulled the check engine bulb out in the dash.

I would replace all the sensors, O2, MAP, TPS, Water Temp and Air Temp. Along with Distributer cap, plugs and wires. Or what’s been coined as a super tune up.
All the above if you haven't already done so. Plus a complete fluid change. Even the brake fluid and clutch fluid. Brake fluid can absorb moisture through the years and your brakes can become spongy.

If you keep track of your maintenance, you'll have a baseline for future work.
When you do your coolant change, it'll be a good time to flush your cooling system and replace the thermostat with an OE Jeep one in the temp range that Jeep recommends.

These old heaps (or any old vehicle) require a lot more TLC than newer vehicles. By the time we get hold of them they've usually been the victim of a lot of deferred maintenance. As you go through the mentioned maintenance tasks, you might see other things that need attention, plus you'll get a better feel for your particular Jeep.

Good Luck, L.M.
Oddly, a PO had removed the bulb but I replaced it and it actually functions normally (lights up when you turn the key on, then goes out). I need to get an ODBI code reader I guess to see if any codes are actually being thrown. The engine seems to be running rich, and is lumpy at idle so it’s surprising a light isn’t being triggered.

I’ve done some substantial maintenance and all fluids have been changed (including radiator), and I keep good records so I have the baseline. I’ll admit I haven’t changed any of the sensors. I’ve been waffling between an engine swap or rebuilding/stroking the current motor. If I keep it, I plan on replacing all the sensors during the rebuild.
 

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Discussion Starter · #7 ·
I just found out about the key trick to get the codes. Turns out I have 3 (technically 4):

12: Battery disconnected in last 50 starts (true, I have done this)
21: Oxygen sensor (makes sense, but weird because this code should trigger a persistent light)
33: A/C relay bad (no factory air)
55: End of codes

I just ordered a NTK 23023 O2 sensor, hopefully that clears everything up. Thanks everyone for the help.
 
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Discussion Starter · #9 ·
Keep us informed
That fixed it. It idles normally and the code has cleared. Can’t tell yet if the gas mileage has improved (only drive it once or twice a week), but time will tell. Thanks everyone for the help!
 
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new sensor in mine but po132 code still there.
Do you have OBD1 or OBD2 diagnostics?
Do you have a code reader?

If you have OBD2 and a code reader you should be able to clear the code manually. Perhaps it requires a certain number of start-stop cycles without the fault that threw the code for the code to clear on it's own.

Good Luck, L.M.
 
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