[DPDISXR4Ti]

I've done 1-wire to 4-wire O2 sensor "conversions" before - it's easy enough to do correctly - I even used a relay.

This question is different. For just a quick & dirty conversion, I wanted to use a 4-wire sensor, but initially just hook up 1-wire for now (obviously, the signal wire). Is this possible, or do I also need the signal ground wire? i.e. With the 4-wire sensor, can the threads function as ground (like a 1-wire sensor), or must I hook both the signal and signal GND wires?

[oharris]

It might work, but why not just hook up the ground and make sure?

[DPDISXR4Ti]

It might work, but why not just hook up the ground and make sure?

This is what ended up doing. I *think* it's required, but I'm not certain as I had an iffy connection at first due to lousy access. When I had more time and better access, I just hooked up the Gnd properly.

Not that this is news, but just in case, I can confirm that there's no issue using a 4-wire sensor in 2-wire mode (no heater circuit).

[cgrey8]

If your computer isn't expecting "quick" O2 functionality on start, then you are right, the heater isn't required.

The heater was added, kind of, as an emissions thing to enable EECs to transition from cold-start open loop to closed loop quicker. I don't have any knowledge of how EECs in the 1/2 wire O2 sensor days worked.

The GUFx defs expected a 3-wire. But my understanding is the 3-wire is the same sensor as a 4-wire with the only difference being the 4-wires have a dedicated wire for sensor return vs using the case of the sensor. I know that was a problem for me when I first got my truck converted. A ground lug between the body and the battery had broken off which caused all kinds of problems with my HEGO sensor values. The HEGOs were trying like hell to output a rich mix, but the ground/sensor return was so bad that the voltage wouldn't quite break the .423v threshold at the EEC and so the EEC thought the engine was running lean all the time and would gradually over-enrich the engine until the point the engine idled like absolute crap including blowing black smoke out the tailpipes. From the datalogs, I could clearly see it was an electrical problem by turning high-current drawing devices on like the dash blower motor or the headlights. When turned on, a noticeable drop in the HEGO voltage could be seen. Once I fixed the ground lug that'd broken off, I never had that problem again.

But I can certainly see the wisdom of having a dedicated ground back to the EEC as opposed to relying on the exhaust pipe(s) to deliver a satisfactory ground connection back to the EEC.