jester1341 said:
i thought that a one wire while wired correctly will run you rich till norm operating temp??
that said is that how the NA works all the time???....dumb
john
Well, what do you mean by "operating temp"? An O2 sensor needs to be at about 600 degrees to operate. The exhaust gases will get it there long before the engine reaches normal temp. This normally happens a few minutes after starting or even sooner if driving.
Heated oxygen sensors were designed to get the sensor there quicker. This was done to put the ECU into closed loop as soon as possible to reduce emissions. A side benefit is it keeps it there should the exhaust temp drop off during low power operations like idle. Looked at another way all the heater does is stabilize the sensor. It's why I said the engine may fall out of closed loop at idle if the exhaust gases don't keep it hot enough.
Since the MK III's OBD I system doesn't monitor the heater for operation not having one won't set any codes. So a 1 wire sensor will work just as well as a 3 wire during all but startup. Your car will simply be running in open loop for a bit longer (maybe a minute or two) after start up and may (but probably won't) revert to open loop at idle. The only possible down side to using a 1 wire is your cat conveter doesn't like open loop but it shouldn't be a problem because the base map in the TCCS should be pretty close in open loop.
You can see what your sensor is doing by putting a voltmeter (or a cheap A/F monitor) on the diagnostic block. It'll be cross counting whenever the ECU is in closed loop. It's important to understand the sensor doesn't cross count on it's own, it's the ECU making fuel corrections (by varying injector duration) and the sensor responding to those corrections that cause cross counting. That's what closed loop means.
If you'd like to know more there are probably thousands of websites on the Net devoted to how an O2 sensor works and what it does..
