3-wire O2 sensor in to 4-wire harness

[CorvallisBMW]

Hey all, trying to wire up an early O2 sensor with a late model harness. The harness has 4 wires: 2 brown, one black and one blue-green. The sensor has 3 wires: 1 green, 1 brown and 1 blue-green. Which ones do I need to connect to each other to make it work correctly? I know there are 2 grounds on the harness and only 1 on the sensor, and I know the green harness wire is the signal wire while the other two are for the heater element. I'm thinking green to green, blue-green to blue-green and then the brown inside the grey sheath on the harness to the brown on the sensor, and wire the 2nd brown to chassis ground. Can anyone confirm? I really don't want to get it mixed up and send 12V and several amps from the heater element in to the ECU lol.

[nando]

I don't think you'll want to do this. the 4 wire sensors are heated, and the ECU is going to expect such. You're likely going to end up with a lot of CELs when the ECU takes a reading and it's way off because the sensor is cold.

[StereoInstaller1]

I don't think you'll want to do this. the 4 wire sensors are heated, and the ECU is going to expect such. You're likely going to end up with a lot of CELs when the ECU takes a reading and it's way off because the sensor is cold.

(where have I heard that advice before...)

[KenC]

When does the heating element actually turn on? At initial start up until the car is warm?
It's in our track car, which is fully warmed up by the time we hit the track. During a ten-hour period, we only turn it off to refuel.

We're planning on just getting a 4-wire btw.

[nando]

it turns on as soon as the car starts, the ECU starts using O2 feedback right away (just a few seconds of warmup).

3 wire sensors use exhaust gasses to keep the O2 warm but exhaust gas temperature varies wildly so often the sensor cools and the reading is off.

any 4 wire bosch narrowband sensor should work BTW. I probably have one with the connector cut off somewhere..

[KenC]

any 4 wire bosch narrowband sensor should work BTW. I probably have one with the connector cut off somewhere..

If you feel like donating it to a lowly LeMons team, we'd graciously accept it :).

[nando]

I'd gladly give it to you. I just have to find it.. lol. what's your timeline? it's fairly new too, maybe 30k on it. I needed the plug for my wideband. :D

[StereoInstaller1]

Nando, the other issue is that since they are using a late harness, they have a 4 wire plug on the harness side and a 3 wire on the sensor side. They need a 4 wire plug too.

[KenC]

I'd gladly give it to you. I just have to find it.. lol. what's your timeline? it's fairly new too, maybe 30k on it. I needed the plug for my wideband. :D

...ASAP? :)

We race at ORP on the 24th

[KenC]

Nando, the other issue is that since they are using a late harness, they have a 4 wire plug on the harness side and a 3 wire on the sensor side. They need a 4 wire plug too.

Can we just run our own leads from the sensor directly into the harness?

[nando]

Can we just run our own leads from the sensor directly into the harness?

yeah, since this is a budget racer you can just crimp the sensor directly to the engine harness. or spend $10 on a connector and pins. lol

I'll try to find it this week. just pay shipping and it's yours.

[KenC]

yeah, since this is a budget racer you can just crimp the sensor directly to the engine harness. or spend $10 on a connector and pins. lol

I'll try to find it this week. just pay shipping and it's yours.

Sweet. Let me know if you find it, as we'll need to go out and buy one if not.

Thanks!

[CorvallisBMW]

Actually the 3-wire IS heated.

The only difference between 3 and 4 wire is that 4 wire has an extra ground for the sensor, where as 3 wire grounds through the exhaust pipe. Otherwise the sensors are identical and the ECU will get the exact same signals, warm or cold.

Check this out:

http://www.unofficialbmw.com/phpBB/viewtopic.php?t=30763

[nando]

I don't know how that will work (well) seeing how the ECU is expecting a signal ground. at the least you'll have a ground offset and a noisy signal. I mean, it will "work", in the most basic sense of the word.

in any case you guys can have my 4 wire sensor as soon as I find it..

[StereoInstaller1]

Actually the 3-wire IS heated.

The only difference between 3 and 4 wire is that 4 wire has an extra ground for the sensor, where as 3 wire grounds through the exhaust pipe. Otherwise the sensors are identical and the ECU will get the exact same signals, warm or cold.

Check this out:
http://www.unofficialbmw.com/phpBB/v...ic.php?t=30763

Darin, that is EXACTLY what I told you yesterday.

Both are heated, but the 4 wire has a "cleaner" signal due to having a separate ground, and is not affected by the spikes in voltage of the heater turning on or off.

Run your 3 wire unless it gives you issues, swap to 4 wire when you get the right one, which sounds like it is right around the corner anyway.