O2 sensors

[jveleven]

I think I may need to replace my O2 sensor. Having a very rich fuel smell in the exhaust. Looks like you can buy them either heated or non-heated. Anyone have any insight on which to get?

 

1989 4.0 manual. 
 

TIA

[jdog]

Do any tests yet or just throwing a sensor at it because it smells rich?

Iirc you want heated

[SoCalManche]

Do you have a REM? If not, this is the O2 sensor test per Cruiser54:

 

O2 sensor testing

1987-1990 Renix

For the Renix years, 87-90, the O2 sensor has 3 wires, 2 black and 1 orange. The orange wire (largest gauge of the 3) is the 12-14 volt power that comes from the O2 sensor heater relay on the passenger side firewall, and that powers the internal heater in the sensor so that the sensor can work at idle, and almost immedietly after start up. Loss of that power will hurt gas mileage even with a good O2 sensor.

One of the black wires is a common ground for the heater power and O2 signal to the ECU, so a poor ground will give a voltage feedback from the heater power input, to the ECU causing poor mileage even with a good O2 sensor.

The third wire, also black is a voltage feed wire, 5 volts, from the ECU to the O2 sensor. The O2 sensor is an O2 concentration sensitive variable resistor. At optimal O2 concentration the 5 volt input feed to the O2 sensor drops to 2.45 volts due to losses across the O2 sensor to ground. That same wire if disconnected from the O2 sensor will read 5 volts constant to ground.

At idle that voltage should read 1-4 volts oscillating quickly back and forth roughly once every second. At 2000 rpm it should run between 2 and 3 volts max, and is optimally running between 2.3 and 2.6 volts at 2000 rpm (in park). A digital meter can NOT be used for reading the O2 sensor voltage, but it can be used to test the ground and the 12-14 volts to the heater and the 5 volt feed from the ECU with power on and engine off. You must use an old style analog meter with the needle gauge on the display to see the voltage swing back and forth with the engine runing.

If the O2 sensor readings are not right, say they read 4 volts or 1 volt steady, you have a problem. BUT before you blame the O2 sensor make sure it has good wiring, and make sure the proper voltage is feeding it, by turning power on, engine off to read the engine off voltage feeds (12-14 volts on the orange wire, and 5 volts on one of the two black wires), and ensure the ground wire (power off) reads less than 1 ohm to the battery negative post.

A leaky exhaust system or leaky fuel injector(s), or bad compression, bad rings or leaky valves, bad plugs, wires, cap, rotor, HV coil, and so on, or combination of these, can also cause a lean or rich condition that gives you high or low O2 sensor readings that are not the O2 sensors fault, so try and verify those other items also before buying parts like an O2 sensor to fix your problem.

[jveleven]

Thank you SoCal.

[Parei_doll_ia]

https://nickintimedesign.com/renix-parts-suggestions/

 

NTKs are usually the go to, but they stopped using a ceramic housing at some point so some have said they're not as good. I just got one and it seems fine so far. The one to avoid is Bosch.

[JaysJeep]

Anyone have a link to the right o2 sensor for an 87 4.0 that they recommend? I can’t seen to find the right NTK for it. 

[rokinn]

Rockauto . https://www.rockauto.com/en/catalog/jeep,1987,comanche,4.0l+242cid+l6,1181483,exhaust+&+emission,oxygen+(o2)+sensor,5132

 

NTK 23553