3 Wire O2?

[sketchman]

Anyone converted? From what I've read the heater circuit runs constantly, so you need no control for it other than engine on power, which is trivial.

The actual part is cheap enough. Anyone with MPG results?

My list of things to do is piling up waiting for good weather, but I just keep finding them.

[Movin]

The 3 wire and four wire heaters are controlled through relays by the engine computer as needed. Probably shortly after closed loop and a certain coolant temp is reached the computer turns the heater off. The 3 and 4 wire do get good readings quicker for better fuel miles but the heater circuit codes are a real common failure.0

A timer of some sort could be used. I would rather put research into the best single wire o2 myself.

[sketchman]

Everything I'm finding says you just leave the heater circuit closed all the time the ignition is on, so that's what I'll do. The actual sensor is $20 shipped on the bay.

Denso 234-3011 for the 3 wire.

[Movin]

I cannot find anything yet to dispute the heater being on all the time. There are different types of o2 sensors that have different operating temp ranges as well as sensor voltage. I assume based on ebay and price that this is an older domestic sensor.

Our literature provided by company reps, the last from standard motor products simply says the heater provides quicker warm ups. For the wide band oem sensors it also says it provides a stable reading during idle conditions.

Our flow chart tests usually show all tests done with key on engine off. I wonder if this is to make sure the computer does not time out the circuit.

And that brings up the question, why do the oem's use the computer to switch the circuit? It would be so much easier to use a non computer circuit. The emissions code can be had by just monitoring the heater, not controlling, so there must be logic , temperature and time that is used to control this circuit, and rpm for some.

I may be wrong but when these first started appearing the seminars we attended I also got the idea of temperature regulating in my head as opposed to on and off with the engine. I have several computer jobs coming in today, I will keep my eyes open.

On the flip side you may be on to something that could improve our city miles per gallon!

[XFSE71]

I like the idea of converting to a heated o2 sensor. As I recall the heated o2s were introduced to keep the engine from going open loop at idle when exhaust temps drop below a critical level. Part of the problem was location of the o2 for engineers. The engine compartment was becoming too crowded. By adding heaters the o2 then could be moved further away from the combustion chamber into the cooler exhaust gasses, allowing more room to move. Since their primary function is to keep the o2 heated at ide, I wonder if we would enjoy any MPG improvement.

[sketchman]

Under low RPM cruise, I'd imagine keeping the PCM in a leaner trim(if it does) would pay off. Like city cruising, or even 35-40 in 5th.

Movin, the part number is for a 95 Chevy C1500 V6. Got it from guys who convert their 1 wire Chevys.

[nitrofarm]

Under low RPM cruise, I'd imagine keeping the PCM in a leaner trim(if it does) would pay off. Like city cruising, or even 35-40 in 5th.

Movin, the part number is for a 95 Chevy C1500 V6. Got it from guys who convert their 1 wire Chevys.

So basically keeping it heated at all times keeps the sensor in its "ideal" reading range @ all times??? Question... what is the 3rd wire for? Why doesn't the 3 wire use the same grd that the single wire does?
Also on a side note,would it be beneficial for fuel economy.If the coolant temp sensor was changed/modified to read @ 15% warmer than actual? I've been tossing this around in my head for a couple months now.

[nitrofarm]

I like the idea of converting to a heated o2 sensor. As I recall the heated o2s were introduced to keep the engine from going open loop at idle when exhaust temps drop below a critical level. Part of the problem was location of the o2 for engineers. The engine compartment was becoming too crowded. By adding heaters the o2 then could be moved further away from the combustion chamber into the cooler exhaust gasses, allowing more room to move. Since their primary function is to keep the o2 heated at ide, I wonder if we would enjoy any MPG improvement.

If this is true,then sketchmans idea holds a lot of value. I have to let my car idle for LONG periods of time in the cold. Sometimes for over an hour at a time. And I notice that it really sucks down the fuel,even with only just the heater on medium and no other electrical load.

[Movin]

Okay, got my data. The heater system does indeed duty cycle after operating temp is reached. Heaters just left on will have the o2 hotter than the ideal temp of 600F. The duty cycle is highly variable and digital square wave just like the fuel injectors have.

To keep this perfect temp of 600F apparently there is a 5 volt test during the off part of the duty cycle. This little test knows that the resistance of the heater varies with temperature and it uses this test to leave it on all the time to warm up or off all the time like during cruise or high speed. Most of the time on trips of less than an hour and in urban or city conditions it will be in duty cycle after the quick warm up. So..there is some smart logic going on.

3 wire and 4 wire sensors do the same thing the difference being the sensor is provided a clean computer ground instead of grounding through the threads . The heater circuit is the same between the two.

To make this work we can rig our own black box logic with a mosfet 555 , some resistors and diodes ( not me, not my area of expertise) or we could cowboy something to work? Maybe something like a clothes dryer thermal switch clamped to the exhaust pipe far enough downstream so that when it cycles it is near 600F at the o2 ?

I think I may have one or two o2 sensors new laying around..

[sketchman]

Or you could do it like the Chevy guys are doing it, and just leave it on.

http://www.thirdgen.org/techboard/tech-general-engine/558978-install-3-wire-heated.html

http://www.fullsizechevy.com/forum/general-discussion/performance/419571-who-converted-their-1-wire-o2-heated-3-wire-o2-sensor-t-worth.html

YMMV

[Movin]

That is different, they are running headers and need a lot of extra heat. BUT, we could weld on bungs down by the inlet to the cat or farther back if your cat is hollow. Its about now that someone is going to suggest we call Matt and order headers, problem solved ! lol

[sketchman]

Haha. Yep, everyone go order a header.

However, what's the worst that could happen? If the heater circuit is wired to heat up to a certain temp, and the exhaust gasses will eventually heat the o2 up to that temp in a factory 1 wire setup, can't it only get as hot as the hottest thing contributing heat to it? I mean, does heating an object with 2 torches make it twice as hot as one torch or just as hot as the hottest temp that one torch can get only quicker?

I don't understand the intricacies or the technicals of exactly how this stuff works. I have only common sense and limited knowledge to work with, so I may be totally off, but it seems like it would work fine in my brain, and the worst that would happen is the heater circuit burns out quicker, but I don't find any mention of that yet.

[nitrofarm]

I'll let Movin Comment but I think if it keeps getting hotter w/o the duty cycle, its going to cause the fuel ratio to become to lean? But if we get lucky it might not be too lean to actually affect drive-ability or worse damage pistons. I would def be willing to try it with a wide band to monitor the situation.

[Movin]

The extra heat would affect things very little after 700F as far as mixture control. But sensor scaling
and heater melt down will probably happen, fairly quickly with one of my trailers on behind! Without a steady load and without headers and in the stock location designed to operate in the 700F range, It is likely at some point the heater would melt.

Thermal switches are cheap and seem to last well I think hose clamping one downstream where it can turn off and on at 200F while the o2 is in range would be cheap insurance.
Especially if we switched to four wire for even better accuracy.

[XFSE71]

I would worry about setting up a 3 wire narrow band sensor hot key on and burning it up because of no interrupt. A clamp on thermal switch is an alternative, but I'm not sure about durability of mousing things like that. We would need a lot of R&D to find the right temp and location. The o2 being overheated will not change AF ratio, because the eca is only looking for the .5V crossing. It may cause the sensor to fail as well. so with or without the heater the AF Ratio will remain unaffected. You can only put so many amps through a resistive media (heater), so it may be self regulating. It's like turning on a hot plate, let it get red hot and walk away. It may still be working when you get back if it's tough enough, or not.

If you hook a voltmeter to your o2 and go drive, you will see closed loop under all conditions except WOT or heavy load and extended idle. Maybe we don't care about heating the o2. just saying.