heated O2 sensor question

[wbx]

I was wondering if there were any FI gurus out there who knew if the heated O2 sensors in the '86 and later vans have some sort of control loop for the heater element, or if they are just hooked to switched power.

I am looking to update the single wire O2 sensor with a 3 or 4 wire version for better emissions and cold weather performance.

-Damon
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'84 Westy (first owner).......but my daily driver has pedals
My "perspective" mantra:
A Volkswagen Vanagon is just a material thing,
As such, it is of the earth,
And if i need to, I can let my Van go.

[buggnuttz]

I installed a heated o2 sensor in my 85. I used a relay turned on by the blue wire off the alt. and got 12 volts from the relay/junction box in the engine compartment ,Fused of course. It increased my mileage by about 1.3 mpg
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owned 39 different VWs so far

[wbx]

[rs4-380]

The heater circuit on all 3 or 4 wire sensors is just a simple 12v circuit (doesn't even matter which wire is grounded and which is 12v+). You can hook it to any ignition switched source, buggnuttz probably hooked it to the alt circuit so it would only heat when the engine was actually running, but it won't hurt the sensor to be heated when the engine is not running (but the ignition is on) and I'm leery of tying things into the alternator exciter circuit.

The only difference between a 3 and 4 wire sensor is that the 4 wire sensor has a wired ground for the sensor head, in a 3 wire it grounds through the exhaust.

If you spend a little time searching you can usually find a "model specific" 02 sensor for cheaper than the universal ones. Usually, the more common the car, the cheaper the o2 sensor, which is why a 3 wire sensor from an 90 or so 4-cyl taurus is usually the cheapest route at you local generic auto parts store.
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Dave
87 EJ25 Syncro GL

[tencentlife]

Damon,

No control, the heat element is powered off the same positive bus as the injectors (Bentley p.97.106, track 26).

[wbx]

Thanks for all the replies - it really sounds easy enough to do!

I'll track down track 26 in the bentley, tencent... thanks for that.

And also thanks for the car recommendation, rs4. I'd imagine the local flaps wouldn't be super keen on me coming in and saying "what's the cheapest O2 sensor you've got?".

"ummm... what kind of car"

-Damon
_________________
'84 Westy (first owner).......but my daily driver has pedals
My "perspective" mantra:
A Volkswagen Vanagon is just a material thing,
As such, it is of the earth,
And if i need to, I can let my Van go.

[buggnuttz]

used the blue wire so that it would only come on with the engine running.
_________________
owned 39 different VWs so far

[kayakwesty]

are the 4 wires straight-forward to know which one is which?

[buggnuttz]

Get a three wire the odd color is the sensor the other two are heater no polarity
_________________
owned 39 different VWs so far

[rs4-380]

yup, the signal will be white, the heater wires will be black.
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Dave
87 EJ25 Syncro GL