0.5 volt dc battery to fool O2 sensor?
 

I have been driving around watching a digital multimeter which is tied in to my one wire oxygen sensor wire (87 civic with feedback carb.)

The feedback system seems to be doing its job (readings jump around but 90% of the readings are below .45 volts when cruising on the highway). When I floor it, readings jump up to 0.8 and when decelerating in gear, readings go down to near zero volts.

I want to fool the system into leaning the mix out a little, so if I could just feed 0.5 volts into the oxygen sensor wire, then the computer would think it was running rich and tell the carb to lean it out.

Its the same theory behind the "fever buster" mod that is listed here on the intake temp thread.

So, I figure that all I need is a good low amp DC 0.5 volt source that will mimic a rich mixture oxygen sensor signal, but won't have enough amps to fry the computer.

Any ideas from the electronics whizzes here? How about if I use a 1.5 volt battery and a ton of resistors in series, might that be safe?

I am not looking to do this long term, just for a 30 mile test run.

Thanks in advance for any help.

You could do it with three equal sized resistors in series. Tap off of the positive of the battery and at the connection between the first and second resistor of the three and you would have exactly 0.5 volts. Then, connect the circuit in series with the wire going to the O2 sensor with the positive going to the ECU side and the negative to the O2 side. You would want to use fairly high value resistors to limit current flow. If you wanted to have some fine adjustment, you could add a variable resistor in the above circuit.

Thanks diamondlarry! But let me double check that I understand how to do this.

So, I have a simple loop with the positive end of a 1.5 volt battery (example AA) connected to three strong resistors in series and then back to the negative end of the same battery.

Then, I run another wire off the positive end of the 1.5volt battery and connect it to the wire that goes to the ECU and I run a wire from the connection between the first and second resistors and run it to the oxygen sensor. So I am forcing the oxygen sensor output in series through this circuit.

Its the resistor junction that I want to double check to be sure I know which one I should use.

The wire that goes to the oxygen sensor, should that be connected between the first and second resistors as viewed from the positive end of the 1.5 volt battery or as viewed from the negative end of the 1.5 volt battery?

Thanks again

It would be the one as viewed from the positive end of the battery. You would want to double-check everything with a multi-meter before making connections to the vehicle.

So you want to fool your computer into running lean... :confused:

Just be careful and I hope you know what your doing... get too lean and you'll be buying a new engine.

I really envy the VX lean burn system and thought I could tinker with one of my own :D

Seriously, I do appreciate the word of caution, yes I'll be listening carefully for spark knock during this limited time test. A few months ago found and patched a leaky vacuum hose (manifold vacuum). It was likely leaking for at least 500 miles.

This is a bad plan. Yes, you can fool the motor, but you will in all likelyhood get the motor to think the o2 sensor is bad. Then it will go into limp mode... and have bad fuel economy.

"lean" burn motors, don't just inject less fuel. they use special valve and combustion chamber setups to make sure that the air fuel ratio is correct near the spark plug.

By running lean, you get MUCH less power for a given amount of fuel. You want to get the greatest amount of power you can from each drop of fuel you burn.

You will get the best fuel economy by burning less gas.. with the correct amount of air. That means using smaller throttle openings. However, by using smaller throttle openings you're reducing the effective compression ratio. That too reduces the amount of power you can extract from a given amount of fuel.

You might consider a very thin copper headgasket and taking great care to avoid using large throttle openings. That would increase the efficancy of your motor at part throttle.

That said, to fool the motor, I would not use straight resistors. I'd use a 100k pot, and a 1mohm resistor, fed off of the battery. Use the 100k pot to get the output voltage you want.

I've been monitoring an '86 one wire sensor tied to a EFI throttle body system (4x4) and it acts just like yours. I was also using a vac gauge and found that unless I kept the vac above 10-12 " HG...the cycling stopped and it went into open loop. With this truck I had to be very attentive to keep it in closed loop during cruise...headwinds and hills were issues.

I doubt if the .5 V added will do the job because as I understand it...the ECU looks for the cycling AND the avg voltage level to determine the mix. You would need to add extra voltage ON TOP of the cycling voltage...which is what an EFIE does.

O2 sensors are tested for being in spec by watching for the number of cycles in say 10 seconds...if they don't cycle enough they are considered as LAZY and need to be replaced.

You could do damage to both your O2 and your ECU if not careful.

It would be nice to find an easy way to add some voltage TO the O2s cycling voltage...but not so sure it can be done.

Running a motor lean can also produce worse emissions. Also, one of the main functions of gasoline is actually to cool the combustion chamber and piston head.

If you use water injection correctly, you should be able to remedy the problems listed above.

Gotta run, I'll post more later.

Cvcc
 

I already have the special combustion chamber/valve setup that you mentioned on my stock CVCC engine. Its a 3 barrel carb that feeds a rich mixture to a mini combustion chamber directly surrounding the spark plug through a tiny extra intake valve and special ports in the intake manifold. The other two barrels work like a normal carb (secondary kicks in as needed) and feed the rest of the cylinder with a lean A/F mix via 2 intake valves.

I am assuming that the feedback carb further leans out the "lean" carb mixture, but I haven't been able to get enough info about this system to know for sure.

The head was shaved when I replaced my head gasket 5 months ago, but the machinist just milled off enough to get it truly flat.

In layman's terms, what is a 100K pot? A 100K resistor? Or a variable resistor like a volume knob on a radio?

I'm not sure if what I have is technically a computer. Its called a "control box". There is no check engine light with this system.

Water injection might be worth a try if it would help me here, but I'm worried that I might end up with too many variables to test at the same time.

I had a mid 80's K car that had a feedback carb that would run fine without ever being plugged in.

The 100K pot is a variable resistor.

I wouldn't recomend doing it this way either, the o2 sensor is part of a looped system, it's a sensor that is performing an important job and bypassing it just seems like a bad idea.
if you want it to run leaner, people have wraped aluminum foil around the out side of the o2 sensor, as they work by reading the differnce between the o2 content of the exaust, and the o2 in the air on the outside of the sensor, so if you limit the amount of of air that comes in contact with the outside vents of the sensor, then it's going to lean out the mix in a controled manner.

Pot is short for potentiometer which is a variable tapped resistor that can be used as a voltage divider.

You don't want to remove the O2 sensor from the system - what you want to do is add a bias to its output to make the ECU think you are running rich so it will lean out the mixture the amount that you bias it towards rich. That may require a little current from a 1 to 1.5 volt? source through a Pot which will allow you to vary how much rich bias you feed the O2 sensor. THis assumes that a rich sensor reads higher voltage and a lean sensor reads lower voltage. You should use about 50x the resistance of the O2 sensor for the pot or even higher so you only apply a 1/50th or less bias relative to the full output of the O2 sensor. You only want a small variation in the A/F mixture.

I need to clarify my earlier post:

I said that in response to the earlier thread that mentioned the car going into limp-home mode. It will still run ok(won't leave you stranded) but it will, if I remember correctly, default to a rich setting which means removing the O2 sensor completely would be a bad thing.

i did this mod with a 4 wire sensor, only i fed a few 10ths of a volt through the o2 ground to raise the voltage at the output.

everyone *****ed at me and no one bothered to actually try it. i wouldn't know how to raise the voltage of a single wire o2, but if you want to install a 4 wire, i can tell you how to do that. pm me.

From what I have read - a 4 wire O2 sensor is a sensor with a heating element in it to warm it up electrically with 12 volts? so it starts working sooner. It can read A/F ratios as long as it is warm enough and by having an electric heating element in it - it doesn't have to wait for the Cat to warm it up to operating temperature.

Makes me wonder if leaving the ignition key on for a few minutes before starting the motor would preheat the O2 sensor more and get it working SOONER thus saving fuel!!!!

I think that you would only need .300V give or take to be effective. Too much would cause an open-loop like condition.

Theres a much more robust way of acomplishing the same thing without resorting to aluminum foil which might destroy an oxygen sensor.

Not sure if the threads are standard on all oxygen sensors (quite possibly are as every car I've changed O2 sensors used the same O2 socket I have...

Anyway, I hate to admit this but back in my racing days when we went to the track we would install track pipes. Basically they were short sections of exhaust pipe that replaced the catalitic converter with a straight pipe. The pipe had a bung in it for an O2 sensor.

Now some people wanted to run this track pipe all year round for the increased performance but running without any cats would set off the CEL.

What they would do is get whats called a spark plug anti-fouler from their local automotive shop (pep boys, advance auto, etc...) They come in two different lengths, long and short. It looks like an extension sort of.. anyway, there are thread on the outside and inside of the adapter. There is alot of excess metal on the inside of the adapter to make the hole small.. you can take a 1" drill bit and drill out the adapter on the long one (make sure not to drill the threads on the inside!!).

All you have to do then is screw the long one into the short one (leaving the short one undrilled) and then screw your O2 sensor into it. Then take the whole assembly and screw it into your exhaust. It will stick out about 2" more than normal so this is only really possible if your O2 sensor isn't sticking out towards the ground (don't want it to hit anything)

It pulls the O2 sensor out of the exhaust path far enough for it to not sense as much exhaust gas, thereby should fool your car into running a bit leaner.

The reason they did it was because running without cats not only made their cars unable to pass emissions but also run richer... this fixes it.

Thanks- I like this idea better than adding extra voltage and possibly frying the oxygen sensor, control box or both. This also seems to preserve some of the functionality of the sensor while leaning things out a little bit.

Maybe I'll get around to setting up this test during the weekend.

The aluminum foil method seems easier, but I don't want to damage the sensor. How/why do you feel this could damage the sensor? Maybe a reaction between the dissimilar metals?

Well with all mods of this type your taking some risk... but IMO aluminum foil is mighty thin and exhaust gas is hot. All it takes is a little corrosion and a bit of it breaking off and lodging in your cat or making its way into your O2 sensor damaging it.

I've used the alum foil with no problems. I think it just insulates it and allows it to stay warmer espec in winter.

For the facts and the original idea:

https://www.lubedev.com/articles/

https://www.lubedev.com/smartgas/

https://www.brightgreen.us/

You guy are putting the aluminum foil on the OUTSIDE of the O2 sensor and cat area to retain the heat right?

I figured that since I am running at a slower speed most of the time and buring less fuel than the standard xB I would need to keep the exhaust warmer to keep the Cat working so I partially wrapped my header by putting foil over its heat shield - not directly on the header pipe. Seems to be standing up very well after more than a year.

The aluminum foil was sounding better but now I am trying to double check the logic behind it and things aren't adding up. Hopefully someone can help me see how the foil is supposed to work in light of the way that o2 sensors work.

This seemed to be a good resource: https://www.aa1car.com/library/o2sensor.htm

So o2 sensors work by looking at the difference in oxygen levels between the exhaust stream and the engine compartment (they are vented through the wire or through the housing around the sensor).

I am going to make up some numbers here-

Lets imagine that the actual oxygen concentration in the engine compartment is an arbitrary number like 10. Looking at the exhaust stream, imagine that ideal combustion is a 3 and a rich mixture would be 2 (less oxygen) a lean mixture would be 4 (more oxygen).

So, if the sensor compares the differences between the engine compartment= 10 and a lean mix= 4, that would be a difference of 6 (so its output would be less than .45 volts).

A rich mix would have a difference of 10-2= 8 (output over .45 volts).

So, if I reduce the amount of oxygen to the outside of the sensor by wrapping it with foil etc., lets imagine that I have lowered o2 to that end of the sensor so that it always sees a level of 8 (rather than the unwrapped value of 10). So now a lean mix would have a difference of 8-4=4 (very low voltage output) and a rich mix would have a difference of 8-2=6 (output still less than .45 volts).

This rich mix (in reality) would be interpreted by the wrapped o2 sensor as a lean mix because it would be outputting less than .45 volts and the computer would compensate by richening the mixture. So wrapping the o2 sensor could be a bad thing for mpg because it could trigger a richer mixture.

I see how the foil could help keep it warm though.

Please correct my logic here.

Inside outside does wrapping the sensor on the outside affect the O2 level of the air that reaches the sensor?? I don't think so! If the air is getting into the sensor via the connector contact it would take a lot of aluminum foil and maybe some silicon sealer to keep the air out. Wrapping can protect it from water and dirt and I don't think it would trap moisture near the sensor because it gets so hot the water would boil off in seconds of starting the engine. Good article on the O2 sensor except for the "voltage to flow" wording - voltage doesn't flow, current flows and in fact it probably produces voltage as the mixture gets richer or its resistance goes up increasing the voltage drop across it from the current supplied from the ECU.

JanGeo- That makes more sense- that the only benefit of the aluminum foil is to retain heat.

If it blocked any o2 from the outside of the sensor (which would be unlikely if o2 came in through the wire), it would seem to have a richening effect (worse mpg) than a leaning effect and helping mpg.

That's what I thought too...but saw no drop in mpg...can't say I had a valid gain either....cause I was doing other things too.

Think it helps in winter...espec with unheated O2s.