Testing Jeep O2, Oxygen sensors

[Ecomike]

I usually coat over it with liquid electrical tape, or self vulcanizing electricians tape when I am finally done, and or do it on the probe connector side when I have choice.

[Ecomike]

I found a good link on this topic topic:

http://www.sjmautotechnik.com/troubl.../10vo2sen.html

Also, I read that pulling the connector on a single fuel injector at a time, (or now that I think of it, a spark plug wire), can be a useful test while watching your live O2 sensor data!!!!!! It would give you useful data on injectors, spark, and the O2 sensors! Same goes for creating a large vacuum leak, by pulling a vacuum line loose, to see if the O2 sensor shows a lean shift, lower voltage. Note that pulling the vacuum line off the renix fuel pressure regulator may make it rich, not lean, and the MAP sensor is not a good one to use either. The Vac line to valve cover is an option on Renix. The idea is to see if the sensor correctly sees the rich or lean shift when it happens. Might also be useful to let an engine idle for 5 minutes, then run the tests, to see if the sensor heater is actually working.

[xjtrailrider]

Mike, my 12 volt supply to the O2 heater only works when the engine is running. Shouldn't have 12-14v when the key is in the running position? I have a good ground and i have a 5v supply to the O2 sensor side but my heater supply is only working when running.

1990, AW4, NP231

[xjbubba]

The O2 heater relay only supplies voltage to the heater during idle and warm-up. It's controlled by the ECM, which looks at the MAP sensor and engine RPMs to determine when to energize the relay.

[Ecomike]

Originally Posted by xjtrailrider

Mike, my 12 volt supply to the O2 heater only works when the engine is running. Shouldn't have 12-14v when the key is in the running position? I have a good ground and i have a 5v supply to the O2 sensor side but my heater supply is only working when running.

1990, AW4, NP231

IIRC, mine had 12 volts in the run position, engine off, but I am not 100% sure. But mine are 87 and 89. As long as it has power with the engine running, I would not be concerned.

[Ecomike]

Originally Posted by xjbubba

The O2 heater relay only supplies voltage to the heater during idle and warm-up. It's controlled by the ECM, which looks at the MAP sensor and engine RPMs to determine when to energize the relay.

Reallly? That is interesting. What years does your statement apply to? Source, reference? Actually verified years?

[XJSteven]

My '96 is the same as xjtrailrider with 12 volt supply only going to the O2 heater after engine start up (and I suspect possibly for a few seconds with the ignition on - I could be wrong but it looks like it's on the same circuit as the fuel pump?).

[Ecomike]

Originally Posted by XJSteven

My '96 is the same as xjtrailrider with 12 volt supply only going to the O2 heater after engine start up (and I suspect possibly for a few seconds with the ignition on - I could be wrong but it looks like it's on the same circuit as the fuel pump?).

I think Renix has 2 different relays, but I do recall that if the start cycle on Renix is not initiated after X minutes, the Renix ECU cuts power to the sensors IIRC. I recall having to cycle the switch after extended tests, maybe 5-10 minutes?

[xjbubba]

Originally Posted by Ecomike

Reallly? That is interesting. What years does your statement apply to? Source, reference? Actually verified years?

Jeep/Renault Component Service Manual, Multipoint Fuel Injection (MPI) systems. Revised January, 1987, page 12 "Oxygen (O2) Sensor Heater Relay".

Battery voltage is supplied to pin 30 of the relay by the ignition switch. The ECM supplies the ground when it feels it's necessary: IE: warm-up and at idle.

[Ecomike]

Originally Posted by xjbubba

Jeep/Renault Component Service Manual, Multipoint Fuel Injection (MPI) systems. Revised January, 1987, page 12 "Oxygen (O2) Sensor Heater Relay".

Battery voltage is supplied to pin 30 of the relay by the ignition switch. The ECM supplies the ground when it feels it's necessary: IE: warm-up and at idle.

OK, so it is grounding the power relay through the ECU. Had to think on that a minute, as the O2 sensor ground is good engine on or off.

[Ecomike]

I frequently forget to mention that people need to check for exhaust leaks, cracked exhaust pipes, and WHY!!!

The O2 sensor compares the exhaust gas O2 concentration to out door ambient air O2 concentrations, and if exhaust gas (which has low O2 levels) is blowing on the O2 sensor exterior from a crack or gasket leak, it can throw off the comparison measurements, and the computer will get miss led think the engine is running too lean, and add and waist fuel, even if the sensor is good and new!!!!!!!!

[CoastieCJ]

Mike, Can you confirm that BOTH the direct ground and the sensor ground should be close to 1ohm or less at the battery on a HO (I've got a 94 for reference). My direct ground (all black) is showing about 1.4 Ohms, but the sensor ground (black w/green stripe that receives ground from pin 4 on the ECU) is showing much more, around 5-6ohm. I notice that all the sensors receive their grounds from this pin. Could there be an internal PCM issue that is causing the higher resistance? Any harm in creating a clean ground for that circuit?
Thanks!

[Ecomike]

I do not have the 94 wiring diagrams handy, so I will assume you have that figured out. Take the two probe ends of the ohm meter and connect them to see what the meter reads. Some read about 1 ohm, instead of zero for a probe to probe short. Take that reading and subtract it from the battery ground test, and that is the real wiring resistance from the jeep to the battery negative post. I suspect nearly one ohm of your reading is the meters internal impedance resistance, and not the jeep ground wire.

5-6 ohms for the sensors ground is too high. I would splice and run a new, extra ground directly to the battery if you can not find the source of the resistance and repair it. That is what I have done on several. have you cleaned and replaced the usual suspect ground wires, like the one at the engine dip stick, and the head to the firewall?

[CoastieCJ]

Thanks Mike! Yes, I've double checked/cleaned all the grounds. I guess my concern is that all the sensors share a common ground, which is sourced to the PCM, not a hard ground point. I assume the PCM switches it internally from one of its ground inputs. But I suppose a ground is a ground! I'll do some more digging and report back.

[Ecomike]

I ran direct ground wires directly from the negative post to both sides of my TPS sensor on my 87 Renix, after fixing all the main system grounds. Made a big difference.