Need to replace O2 sensor. Couple of questions...

[tirwin]

Hey, folks -

I got my WUR back from being recalibrated and while I was in there I was checking out the O2 sensor connection. The male end of the connection, like so many others, has completely disintegrated. Car is an '83.

Thinking now is a good time to replace with a wideband O2 and AFR gauge with narrowband output.

Does the other end of the O2 sensor connect to the relay under the passenger seat?

If so, can I just cut off the broken male end of the connection and splice in the narrowband output from the AFR gauge?

[tirwin]

Looking at this one... any comments or experience?

https://www.plxdevices.com/product_info.php?id=WDBDSMAFR_DM6

[James Brown]

sounds like a good plan, not sure where the O2 wire ties into the control box but that should be a easy look up. you have a Bentley

[A horse with no name]

Hi ...It looks interesting. How do you view the different readings? Does it have a menu button that pulls up each individual input such as volts - or? - Thanks.

[tirwin]

It looks like it's a touch screen and you tap on the left side to cycle through. The video shows 4 modules installed on a Lambo - 2 AFR and 2 exhaust temp (2 on each bank of cylinders) and you can cycle through. I only need one for now but if I go for SSIs then I could put one on each side.

[tirwin]

Well I ordered the one above. I'll see how it goes and report back. I'm not home or I could look in Bentley. I just thought someone might know off hand how the wiring works.

[psalt]

The O2 sensor signal wire connects to Pin 2 on the Lambda ECU. The factory wire is shielded and the outer shielding is connected to Pin 4. The wire is shielded because the signal is less than 1 volt, it travels several feet to the ECU under the passenger seat, and the system works off of variations of less than 100 mv. There is some crazy voodoo nonsense on this site that air travels up the shielding. I suggest you monitor the voltage at Pin 2 with the old narrow band sensor before switching to the wide band NB emulator. I my experience there are variations and most good programmable EFI systems let you adjust the target in the software.

[tirwin]

Psalt,

Good stuff. I am not entirely sure the O2 sensor is working. That's what I was in the process of working on when I discovered the connection was broken. I just read recently that the duty cycle defaults to 50% when the O2 is in open loop (disconnected). That is what I'm seeing right now when I monitor at the test port.

So in order to do as you suggest, I'd have to rig up a temp connection to the old O2 sensor and then determine if it works or not. If I understand it correctly, the O2 isn't used at idle or WOT, so I'd have to rev the engine with the dwell meter hooked up to the test port to see it "dither" the frequency valve.

My next question is what are the failure modes for a bad O2? If it's completely dead I assume that's effectively the same as open loop? Is there some other way to verify the sensor is in spec like testing with a multimeter?

As always, thanks in advance!

[psalt]

You should do a little more reading about the system, I suggest starting with the Bosch manual, then Probst book, much of which can be found online, if you are good at searching. There are some Porsche specific things on a 83 911 SC which you will not find much about. Unfortunately the Bentley manual is incomplete and has several errors. There are at least four "default" open loop duty cycles on your 83 ECU (cold idle, hot, >35% throttle, cold accel, etc), none of them are 50%. The O2 sensor is active at idle, but there is another switch to provide a delay to limit the rpm fluctuations. A new 83 SC had a fluctuating idle, this gets worse with neglect and leaking injector sleeves, so some anal idle twiddlers disconnect the sensor to "improve" things. You can test the O2 sensor by hooking up a dwell meter and watching the system go into closed loop and start fluctuation. If your engine does not go into closed loop, start by diagnosing the temperature switch, the ECU, the throttle switches and the sensor. You can hook up a voltmeter to the center conductor of the O2 sensor with the engine hot and you should see 600-900 mv.