I could really use some help on this.... My passenger side O2 sensor is not fluctuating--it's staying at 457mv (my driver side O2 is working fine). I just replaced both sensors with AC Delcos, and I switched the sensors to confirm that they are both good. I tested continuity of all the wires on my O2 extension harness and tested continuity on the purple and tan wires leading to the computer. So... I have it narrowed down to the heater power/ground wires. I know the power comes from a 10a fuse---I checked both fuses and they are ok (not sure which one runs the O2's). Can anyone tell me where the ground wire for the passenger O2 sensor terminates?? I think that's where my problem is. Thanks....

 

O2s are grounded on the coil stud.

 

Thanks for the reply, Shoebox... I tried testing continuity but now I'm confused. I put one probe in Pin C from the connector to the PCM and one on either of the tan wires attached to the coil stud and I get a tone. In fact, from Pin C, if I touch any part of the car (like the alternator) I get a tone. I tested the driver side Pin C and it's doing the same thing. Is this normal or is it telling me that I have a short in the harness???? What should my next step be (not sure how to test the power line). Thanks....

 

That would be normal. Your are getting a ground at all those places like it should be. An actual ohm reading should be taken, rather than just relying on a tone.

 

Ok... I took Ohm readings from my harness to the PCM and both wires read .1 I also checked each wire on my O2 extension harness and each wire read between .1 and .3 I also checked power on Pin D and I'm getting 11.4v. So, what now?? Is this a PCM problem?? I'm using Datamaster to check the O2s and when the car goes into close loop the passenger side LT BLM hits 160 and stays there--I can smell the fuel being dumped in. The O2 sensor does move in it's readings but VERY slowly. This is causing the car to run really bad---no power, backfires, and stalls.

 

When an O2 is unplugged, the PCM will default (so to speak) to around 450. So it would appear that the signal wire is broken. I know, you tested it for continuity. But here is what you need to do. By grounding the signal the PCM should show a low voltage. Below 100. if it does not, it will prove you have a broken wire.

To do it, unplug the O2 and jump from the tan/white to ppl/white to black wire pins. ALL 3 connected together. The PCM should read low voltage. If not you have a break. The first place to check is where the harness goes down the inner fender and is wrapped with foil insulation. Check the wires in there to see if they got cooked from your headers.

If that bundle is still located there, I guarantee they got cooked.

 

I jumped the pins and got a reading of 4. I removed the jumper and it read 457. When I said it was "stuck" at 457 that was incorrect. After making a couple logs, the sensor is moving but very slowly. I just ran the car for 5 minutes and the sensor stayed between 100 and 228mv--sometimes it will stay at one number for several seconds. Also, the car is not going in closed loop now... I tried reseting the computer but that didn't work. I have inspected the wiring and nothing is burned--everything has been wrapped in heat tape and tied up away from the headers. So...any other suggestions? Should I try reflashing my computer? Are there any other readings that I could provide to help??

 

i guess your old o2 sensor was acting the same way?

 

Actually, I think this started last year. It's been 7 years since my build and the last few years the car has not been running right (I've put 12,000 miles on the car over the last 7 years---it's a toy). The O2 sensors have always been a problem--this is my 4th set. I have been running Bosch sensors which I think has been my problem, however now, I think my PCM might be the issue. Either way, it's been real frustrating trying to fix the gremlins of this car! If it wasn't for this site, I would have sold the car 8 years ago.... Keep the ideas coming guys, I need to get this thing fixed--this car has great potential......

 

After years of doing this type of thing, I can tell you 2 things. I have never seen a defective OBDI PCM. The other is none of my vehicles will work with BOSCH O2s.

 

I'm am strugling with a similar problem. If you figure it out let us know.

 

I responded back by PM that you need to unplug an O2 and drive it. This will force the engine to operate in open loop all the time. If you still have a fuel issue, then you need to look at other items.

If it does not have an issue in open loop, then we need to look at your O2 system again. The first place to start is to get rid of the Bosch O2s and get Standard Auto made for GM/AC/Delphi units.

 

You seem to feel the problem is the wiring, and there is no possibility there is actually something causing it to run lean. How did you rule out a true lean condition?

 

You're right.... I totally overlooked that possibility--it makes sense now. In the past, I had a heck of a time with sealing my headers--Percy's, Felpro 1406, and in the end I doubled up the Felpros and used copper RTV. If the header gasket is blown, would that be enough to keep the O2 sensor at a low range and not to fluctuate, thereby pegging my LT BLM to 160 and dumping fuel??

Speedy: I did change over to new AC Delcos. If I find my header gasket is ok, I'll drive it in open loop and report back.

 

Aren't most sealants bad for O2's? Did the copper RTV say it was O2 safe?

Wouldn't a leak bad enough to effect the O2 be loud enough to hear?

I have a hard time seeing how a leak that is usually under pressure allow air to enter anyway.

Sounds a little far fetched to me other than the goop you used to seal it messing up the O2's.