Still no O2 Sensor voltage?!?


Ok guys,

Still having trouble. Replaced the suspect heated O2 sensor with a standard O2 sensor. Started the car and plugged in Turbolink. Still not getting any O2 voltage. Car runs fairly smooth but blows a lot of smoke when throttled. Running extremely rich. Pulled a plug and it is black as coal. Is there anywhere I can back probe O2 sensor circuit to check for voltage? I am not too sure if I should believe the Turbolink or not. Air/Fuel gage is only bouncing between Stoich and Lean... which would cause the rich condition. BLM's are @ 178... way too high! Any help would be appreciated!


Check your grounds behind the passenger head. One of the wires is the O2 sensor ground reference. Mine was loose and I had very low readings.
Grounds on the head? I dont think there are any grounds on my rear passenger head. Hmm. Is there any way I can verify ground in harness by the pigtail? Where does this ground come from?

Just a s a background, Here's the story:

I had a heated O2 sensor in the car. Well, had a friend help me under the hood and I am sure that you have seen the 2 pigtails that look identical to one another. One is a 12 v feed from battery, one is the O2 pigtail. Long story short, he swapped the 2. Car wouldnt fire. Took me 3 hours to figure out what happened. Swapped them back and car fired right up. Like I said, no O2 voltage readings on Turbolink now.
1. Disconnect your air/fuel gauge.
2. Check the tan wire attached to the black/white stripe wires at the passenger side rear cyl. head. Be sure it's grounded well.
3. Check continuity of the purple wire O2 signal to ECM.
4. Leave your air/fuel gauge disconnected permanently.
So I am understanding 2 things:

1. There is a tan wire that attaches to a black/white striped wire that is supposed to be mounted on the passenger rear cylinder head?

2. The air/fuel gage is ****. :biggrin:

Please advise?

Yep. Tan wire is sensor return, and must be grounded for the sensor to link to the ECM.

Most AF gauges tap into the signal wire and skew the sensitivity of the sensor. I would not attach any device to the O2 signal wire.

If that wire is not on the pass. cylinder head, can I just follow that tan wire (from ECU) and ground it to a chassis ground in/outside the car? Like I mentioned before, I dont remember seeing any ground wires attached there.

i guess the A/F gage is coming out! Hey, anyone have a Scanmaster they want to get rid of?

while I got you here... I have 2 of your products. I have one of your TPS techs and your 8 position chip. I think my TPS tech isnt working. None of the lights are lighting up on the box. I tried to set my TPS by using both a DMM and the LED on the box. Set the TPS but no light. Can I send it back to you to verify that it is ok?

Also, my 8-pos chip that I have is set up for my 50lb injectors. I think I may be dumping too much fuel. Is there any way I could send you that to pull some fuel out of the chip as well? I will try to tune before I send it to you but just wanted to know if that was possible.



Ok kids,

Just got back from my garage a little bit ago. I verified wether the O2 sensor had voltage. Here are my findings:

O2 sensor wire from ECU plug to O2 sensor harness: good
Ground wire from ECU (O2 signal) to engine ground: good

back probed O2 sensor wire from ECU and turned key: 223mV reference voltage.

Started car and let run for about 5 minutes and backprobed O2 sensor wire from ECU: DMM was bouncing from 100mV to like 890mV.

The only thing that threw me off is that every once in a while, the car would shutter a little. When that happened, the O2 voltage would drop to 0.

It seems as if the O2 sensor is working but I am still confused as to why I could not read the O2 sensor voltage through my Turbolink. Maybe bad connection on ALDL connector?

Car is still running rich as hell too!

Any advice?

I verified the wiring so I dont think that is it. Both ECM harness are brand new and computer is brand new as well. I am not too sure what is going on here... :frown:
I verified the wiring so I dont think that is it. Both ECM harness are brand new and computer is brand new as well. I am not too sure what is going on here... :frown:

Did you verify that the o2 wire is in the right position in the ecm plug. Shoud be coming in on D7. ECM Connectors
Where did you get the harness? New used or brand new?


Yes, O2 signal is coming to D7 on the harness. The harness is brand new. I got it from a local GN guy here. It was John Spina's harness (Casper's Electronics)

Another ECM would help narrow it down. If you swap and it still has no reading then it has to be in the harness. ;)