Cant find my o2 problem?

[Boostmonkey]

Hey,

I tried to get my car cal smogged the other day, and it pulled 3 codes and failed, both front and back o2 sensor codes, and the front o2 heater code.

My first thought was sure both o2 sensors were bad. It seemed possible that if one went bad for some reason, that the second would be soon to follow. after a few hours searching here i decided to just change out the front one and get an elim circuit for the rear (cheaper) .0 So i grabbed a working one from a local dsm wrecking yard.. but on the way home i realized my blinky a/f gauge was working fine. it was flopping back and forth between rich and lean after it hung out a while to get warm just like a working o2 sensor is supposed to do according to what i read here:

O2 Sensor FAQ (found on a faq on here)...

That lead me to believe there was a problem with both? sensors wiring? I took a multimeter, and from the front sensor plug i traced the 2 wires (front o2, and front o2 heater) back to their corresponding pins(76, 60) on the ecu, and had continuity.. i inspected the outside of the rear sensor and the wiring and it all seemed fine going up under the seat and into the plug for the ecu.

Now im not sure where the problem is. If my sensor was bad wouldnt my a/f gauge not work normally? and if there is continuity from the sensors plug back to the ecu harness, then the only thing left is the ecu itself? There must be something im missing as it seems a little strange to me that if there was a failure on the ecu, that it would throw those random codes up and only affect that particular part of all its responsibilities.

Tomorrow i will pull the original sensor off after i verify the junk yard one using the above method, and replace them to see if that makes a difference. then i guess ill inspect all the pins on the ecu connectors and the sensor connectors i guess, although they seem very sturdy.

If anyone has any ideas on something i might be missing or any insight as to what is happening that would be awesomely helpful.


Thanks,,

Dave

 

[Spyder4g64]

I had my front o2 and rear o2 harness side plugs switched for a long time until i got DSMLink, and could read both. Its a stupid guess, i know, but it doesn't hurt to check it out.

 

[luv2rallye]

Possibility: On a 2g (but not 1g) ECU pin 92 goes to the signal grounds of the following engine sensors: manifold diff pressure, engine coolant temp, front O2, rear O2, TPS, volume air flow, and fuel tank diff pressure. Pin 92 is grounded inside the ECU but all these sensors signal grounds must NOT be grounded anywhere but through pin 92 to avoid electrical noise and ground loops from affecting the sensors differential signals - ie. voltage between each of these sensors signal and signal ground. Some people and even some mechanics, don't know/realize this and they mistakenly connect signal ground to the engine (as in a 1g). A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine/chassis (or even battery negative) can cause misleading and noisy signals to the ECU causing the ECU to run the engine poorly. And if it is still also connected to the original harness signal ground wire, then all of the above engine sensors will also have that problem.

 

[Boostmonkey]

Hmm,


Thanks for the quick replies guys, this is the best community out there.

^^ Harness side plugs? as in the ones going from
sensor>wire on sensor >(connector)>wire>(ecu plug)> ecu?

as in the (connector) above could be plugged in incorrectly? i guess swapping all my pins around?

I verified the wires from the ecu connector all the way to the (connector) above, and they all had proper continuity to their corresponding pins on the ecu, so im pretty certain that unless the wire on sensor is plugged into the (connector) incorrectly... and thanks that is something i will check out today.


^ Could it possibly be that i tapped my a/f gauge into a closer ground than the recommended pin 92? its possible that it is communicating ground crap to the signal wires, that makes sense to me. ill unplug / relocate the a/f gauge.. then report back.



Thanks for all the ideas and help. it is greatly appreciated.

DAve

 

[luv2rallye]

When you unplug the ECU (disconnect battery 1st for ECU safety) there should now be no continuity (not near 0 ohms) from the ECU harness side connector pin 92 to ground. If there is someone grounded one of the signal grounds of the above sensors. I don't think changing your A/F signal ground will make any difference unless it was connected to the other sensor signal grounds as well as engine ground.

Here is the correct O2 wiring (note that signal ground and heater ground are not the same thing): http://www.dsmtuners.com/forums/articles-electrical-wiring/244376-oxygen-sensor-wiring.html.

 

[jake247]

^ Could it possibly be that i tapped my a/f gauge into a closer ground than the recommended pin 92? its possible that it is communicating ground crap to the signal wires, that makes sense to me. ill unplug / relocate the a/f gauge.. then report back.

did you install your a/f since your last inspection (since the inspection station reads your CEL codes for you and told you that your check engien light is on because of o2 sensors)-- that is to say, is it possible that the installation of the a/f gauge is what is causing this problem?