Oxygen sonsor - multiple wires
 

Hey folks,

I'm doing a bunch of stuff to an '89 Ranger, (with 4 cyl engine) i.e. new flywheel, new clutch, new cat converter and pipe. I'm getting ready to put a different exhaust manifold on this truck that I got from a salvage yard. (That's because I couldn't get the bolts out that connected the cat pipe to the manifold. Tried heating, tried drilling. tried bolt extractors, and nothing would work.)

So anyway, this used manifold I got still had an O2 sensor in it. I benched tested it with meter and torch and it passes. My old O2 sensor failed the test. So maybe I lucked out by getting a good sensor with this old manifold. The used manifold (with the sensor) cost $35 which is about what a new sensor alone would cost!

Problem is: this extra sensor has 4 wires but my old one only has 3 wires. Both have the black signal wire, and both have two white wires which I guess are the heater. The extra sensor has a grey wire as well, that being the extra wire.

So my question is: can I use this spare sensor and just assume that extra grey wire is something my truck doesn't use? Or is that a bad idea? I figure it can't hurt to try it.

David

Two wires for the heater
two wires for the sensor.
I doubt you can use it as it must be for a different year.

The sensor circuit of the early 1 wire (unheated) and 3-wire (heated) sensors were supplied chassis ground by way of the exhaust system - not the most reliable way to do it over the long term. Later 4-wire systems use a dedicated ground wire that runs all the way back to the PCM to make sure that there is no difference in ground level at the sensor vs at the PCM as the system ages. That's what the gray wire is for.

Very useful info, Bob. Thanks. I may just try this old 4-wire sensor and tie the grey ground wire to chassis somewhere myself. Can't hurt. If it works, I save about $40.