02 Sensor question
 

With the new exhaust, I'm going to re-introduce an oxygen sensor to my (confused and lonely) DME computer. My 3.2 headers have an old (disconnected) one-wire unit. I just got a good deal on a new 3-wire unit.

Part numbers:
Porsche 965-606-126-01
Bosch 0 258 003 924

For some reason, I have it in my head that it's supposed to be a four-wire sensor. I'm wrong, right?

I don't know, Jack, but I've never heard of a 4-wire O2 sensor. They probably exist, but not in my experience.

Jack,

How about a 3 wire sensor? One wire to the sensor (I assume) for information to the DME computer and two wires to the heater on the sensor. Could be the other way around as well with two for the sensor and using the exhaust for the ground on the heater. The earlier sensors did not have the heated sensor and supposedly did not read properly until warmed up.

To meet emissions they had to heat the sensor to read correctly from startup and used a heater. My 85 model has the three wire and the later ones do as well.

Joe

Jack - my '86 has a 3 wire but I run the car with it disconnected (Autothority Mass Air/Chip with B&B exhaust). I connected it last year to determine if an benefit - while little affect to idle it dramatically reduced low end acceleration and part throttle response.

I too have never heard of a 4 wire sensor. I know the generic bosch sensor that you can buy for much less than the one designated for the 911 is a 3 wire sensor.

Back in the late 80's I worked for a company (the same guys that mfr the 911 FI systems).

The first type of sensors were the 1 wire, which just supplied a signal wire to the Electronic control module (ECM). The ground for the signal went through the exhaust system. I believe that the Volvo was the first MFR to have an O2 sensor in their production car.

Then there were 2 wire sensors, where the 2nd wire was the ground for the signal wire. These were somewhat rare.

Then the 3 wire sensors came out. These had 2 white wires and one black signal wire. Of course the ground was through the exhaust system.

ASAIK, Then Ford decided that they need to remove some of the ground noise in the system, so a 4 wire sensor was developed. The signal voltage and the signal ground is seperate from the case. This was a good idea, except other items were attached to this "good ground" and some of the benefits were lost (IMHO).

Anyway, to answer the question, yes there are 4 wire sensors, but IMHO, 3 wire sensors are just as good. If one would try to install a 4 wire sensor into a 3 wire sensor system, ground loops could be developed, thereby causing a bunch of problems. For most 3.2 DME systems, a 3 wire O2 sensors was the one that was used.

Oh, and when I was working there, I developed a method to tell if the 4 wire sensor was manufactured with reverse polarity on the signal part. Unfortunately, I was not smart enough to get the process/method/system for testing patented... Oh well.

Thanks. Four wires just doesn't make sense. I think the wiring problem must be in my cerebral cortex. :)

I think the 3 wires sensor is 1 black wire and 2 white wires. The black wire is for signal and the 2 white wires are for the heater. I just did this job on a VW GTI last weekend.

A four wire sensor will work just fine since the extra wire is only a dedicated ground for the 02 signal.

I've been using a four wire sensor on my 86 Carrera for the last four years without any problems and was told that these new generation four wire sensors were more reliable, lasting much longer.

I believe the one I have came out of a Dodge minivan, compliments of our local auto dismantler which was a hard deal to pass up.

Cheers,

Joe