Making Your Own Air/fuel Meter

[Trev]

do you have to mount a bung on the exhaust manifold? or can you insert it in the exhaust pipe like they do on the dyno's?

 

Exhaust tip clamp.

[altezzaclub]

You're right in a way Trev- I was thinking of hitting the wreckers to see if I could circumvent the $100odd for a sensor

 

This is what got me interested in it to start with- a gauge under $40 and a narrowband sensor for $40....

 

http://home.hiwaay.net/~langford/corvair/o2meter/

 

Unfortunately technology and prices have moved upwards! :(

[Evan G]

http://autospeed.com.au/cms/title_InCar-Ai...32/article.html

 

check that out, Mixture Display Kit for Fuel Injected Cars (Silicon Chip/Jaycar) Price: AUD$14.95.

[altezzaclub]

Yes, I started out with that idea Evan, then I learnt more...

 

So, what do we need for that? The $20 kit, a sensor, and.... do we need a controller like the Jaycar $80 one I posted up on page 1? Some cabling that I can cut out of a car at the wreckers with a wideband sensor on the end??

 

Any ideas on which model of car would do this?

Edited July 11, 2010 by altezzaclub

[snot35]

He doesn't have a fuel injected car.

 

I think you'd be able to do OK tuning with a narrow. Certainly much better than tuning by feel. If you can spare the money though, the wideband is something that will be in the toolkit, and be very handy, for a very long time!

 

Get the tech edge 2J. It's already built and is a plug in proposition. If you can scrounge an old laptop and drop the display it's only a bit more expensive. The 2Y is a kit. If you're confident with electronics it'd be fine. Otherwise it will probably cost you a penny to get it built.

[altezzaclub]

Yeah, the Techedge is the best of the smart ones Snot, so that budget is $250+.

 

I'll never need it after I tune the SUs on the KE70, I don't expect to build another car in my lifetime, and I wouldn't know how to hook the laptop I don't own into it. I can see that for you young guys they are indespensible tuning tools these days, but car computers and fuel injection is completely beyond me.

 

So It looks like the Jaycar LEDs and a narrowband sensor will do it. I'm unimpressed by what I've read about setting the rich & lean endpoints, they don't seem very scientific in their ideas of how to make it run lean or rich while you adjust it. I suppose the best way is to calibrate it against a proper machine in a dyno shop. Then again with SUs I can wind the jet up until it dies from being too lean and just pull the choke out for rich.

 

This is Dirtcheap Garages Ltd! :(

[philbey]

yeh I looked at buying these a while ago, everyone raves about the Techedge units although their website and general presentation is.... dated.

 

I was pretty keen on shipping an Innovate in as well, the local prices on them were shit. I reckon I read someone here on the RC had really bad experience with the innovate unit failing though.

 

I would like to dabble with E85 some day so that was my motivation for buying one of these suckers.

[Trev]

He doesn't have a fuel injected car.

 

Don't know what that has to do with it.

 

 

yeh I looked at buying these a while ago, everyone raves about the Techedge units although their website and general presentation is.... dated.

 

I was pretty keen on shipping an Innovate in as well, the local prices on them were shit. I reckon I read someone here on the RC had really bad experience with the innovate unit failing though.

 

Look at the dudes profiles that make it :(

 

I think that was me tho I would of been talking about the OBD part of it not updating correctly to work on all cars, If this happens you need to make a backup on your computer and send it to innovate.

[Felix]

Don't know what that has to do with it.

 

Maybe he means that seeing as carbs are an analog device, and the motor is not boosted, a wideband is not a necessity.

 

I put a narrowband in my ke15 with one of those Jaycar FMD's. Cost... $100 all up (about 6 years ago). Shitloads better than stumbling in the dark. The numbers may not be exact, but you have a definite guide as to which way your tuning changes are going.

 

Once you have it set up it is a simple task to upgrade to a wideband o2 sensor and to fit the wideband controller.

 

Anyway, personally I'm thinking of getting one of those LM-2 Kits at a later stage.

Edited July 12, 2010 by Felix

[altezzaclub]

Aha! Tell me about it Felix! Which Jaycar unit was that? Is it wired in or do you put it in the tailpipe? What did the narrowband sensor come off?

 

What else did you need to get it fitted and running? Got any photos??

[camerondownunder88]

Hello,

Just adding what I have.

 

With the narrow band yes not the best for tuning but better than nothing once you have a rough setup for carbies this can help fine tune them a bit more.

 

As for the kits I am currently building one atm. At the end of finance year I got a wide band fuel meter kit for Half price :( so like $35 I think it was CHEAP.

 

Jump on evil bay. $100 will get you a wide band sensor :D

 

Then jaycar now make a kit for the wide band controller for under $100 (think I saw it at $69 other day)

 

So for me about $190 I will have a full wide band setup.

 

But then the wide band jaycar kit pull out the O2 sensor and any sensor with a 0-5 volt range will plug n and it will read it :D

 

So with some tuning and that I could adapt this to a oil pressure, fuel pressure, vac gauge etc the list goes one your imagination limits you only. So es initially could cost $200+ for jaycar setup but uses down the track HEAPS.

 

And the wide band kit straight out of the box will read narrow band sensors so even if you can't afford a wide band sensor and controller straight away hey can still get a cheap narrow band sensor and start tuning. As a rich running carbie can kill an engine fast if left to run rich. And I am sure the motor being re-built cost more than tuning the carbies correctly.

 

Cheers

Cameron

[altezzaclub]

Well done Cam! What one did you get? ...and when do you reckon you will build it?

 

here's some explanations for everyone reading this. The pictures are on here-

 

http://wbo2.com/lsu/lsuworks.htm

 

As we will see, the wideband sensor is operated by current that is pumped into or out of the pump cell by the wideband controller electronics. This is fundamentally different to a narrowband sensor that produces its narrowband voltage, without any external electronics, when heated to operating temperature. To understand wideband, we must first understand narrowband sensors:

 

Narrow Band Sensors

 

Narrowband sensors have between one and four wires. One of the wires will always be the signal voltage. A second wire can be used to isolate the ground end of the signal to reduce signal noise. Three and four wire sensors add a heating element so the sensor starts operating faster and more reliably.

 

The image at left shows a representation of a 4-wire version - in practical narrowband designs the sensor is often shaped as a thimble to maximise surface area exposed to the exhaust gas. The electrical heater is used to raise the temperature of the Zirconium Dioxide (ZrO2) material that the sensor element is made from.

 

Zirconium Dioxide (often doped with Yttrium oxide) is an important substance that maintains mechanical rigidity while capable of conducting an electric current when in a molten (red hot) state. The sensor current is carried by oxygen ions that become available only when the sensor is hot enough. The Platinum covering is both conductive and promotes a catalytic reaction between oxygen ions and partially burned fuel. The Nernst equation describes the voltage produced as a result of this catalytic reaction involving Oxygen ions, Platinum catalyst and exhaust gas.

 

* Vs = (RT/4F)*ln(pO2air/pO2exh) pO2 = partial pressure across gas boundary

 

The pO2xxx is the partial pressure of oxygen, and is a convenient representation of the oxygen concentration on each side of the oxygen sensor. The RT/4F term can be thought of as a constant multiplied by temperature T.

What this equation says is that with rich mixtures, where there's almost no oxygen, but lots of free fuel, the voltage Vs produced by the sensor will be fairly high. Around stoich some free oxygen becomes available and the voltage produced by the sensor rapidly drops. The graph at left shows how Vs rapidly switches from a voltage around 0.9 Volts to around 0.1 Volt over a very small Lambda (or AFR) range. This rapid switching is one reason narrowband sensors are not accurate in the rich region, where most power tuning takes place.

 

The equation also says that at higher temperatures Vs will also be higher. This is shown in the image at right. It is the other major reason why narrowband sensors are not very accurate away from stoich. As the load on the motor varies, the temperature of the sensor will change, and it will read a different value, although the actual Lambda (or AFR) has not changed. It is possible to temperature compensate by measuring the impedance of the sensor and calculating its average temperature, and this is what most better quality Lambda meters, that use a narrow band sensor (such as the LSM-11), do in order to improve their accuracy.

Pump Cell

 

The narrowband sensor, described above, detects the voltage Vs produced by the Nernst Cell. It is possible to force a current through the molten electrolyte and to drive the chemical reaction such that oxygen is pumped (in the form of o2- ions) from one side of the cell to the other.

 

* O2 + 4e- —> 2 O2-

 

In a rich mixture the oxygen ions will combine, on the pump cell's catalytic surface, with fuel to produce water and carbon dioxide. When all the fuel is consumed there will be no free oxygen and the resulting mixture will be at stoich. In a lean mixture (or even in free air) the pump current is reversed and the free oxygen is pumped out until none remains, and the resulting mixture will also be at stoich.

The image at right shows a pump cell and a small chamber that exhaust gas can enter. The rich, or lean, gas inside the chamber can be reduced, or oxidised, to produce a stoich mixture. An important part of the pump cell is the size of the pump cells entry hole and width of the diffusion chamber. As these are all subject to manufacturing variations, spreads in operating parameters are expected, and a scheme to allow for this variation is required.

Combining Narrow Band and Pump Cells —> 5-wire Sensor

 

Combining the narrow band and the pump cells allows the narrowband sensor to sense the mixture resulting from pumping oxygen into or out of the diffusion chamber. The resulting sensor is shown at left. To save wires, the Vs (sense) and the Ip (pump) cells are connected together - they share a common reaction surface anyway, so this isn't a problem.

The manufacturing variation problem, which results in sensors of varying sensitivities (differing pump currents for the same Lambda), is solved by adding a calibration component. A resistor (Rcal) is laser trimmed after the sensor is constructed and tested. The laser burns away material and increases the value of the resistor until a standard Ip current is produced at a known Lambda value. If this circuit is reproduced in the controller itself then each sensor will be automatically calibrated without further calibration. Obviously, as each sensor is factory calibrated, and the calibration component is usually in the sensor connector itself, if someone removes the connector, then the sensor has become uncalibrated!

 

Many controllers do not have this circuit and they must go through a free-air calibration phase to work accurately. Note also that all pump-cell wideband sensors will have at least 5 wires from the sensor. Six or 7 wires will come from the connector (some sensors use a calibration resistor in the connector that has both ends free).

 

Some things to note are that when the sensor is being actively controlled, the mixture in the diffusion chamber is at stoich and the Vs voltage is close to 450 mVolts. There is a small self-pumping effect of atmospheric oxygen into the diffusion chamber by the Vs sensor part, but this is much smaller than the pump cell's action. As atmospheric oxygen concentration (ie. free-air) is used as the reference on one side of the Vs cell, then the flow of air to the back of the sensor must be maintained - this is usually via the sheath covering the wires to/from the sensor. The wire sheath should not be constricted!

[Felix]

The kit I used was an older Jaycar/DSE narrowband FMD kit (DSE was the one I used). I got an M18x1.5 nut and ground it to suit the outside of the exhaust after the extractors. Got it drilled and welded for a 6 pack. Used a second hand EB falcon heated 3 wire o2 sensor.

 

Edited July 12, 2010 by Felix

[Evan G]

your last picture of your ke15 says rolla LOL!

[altezzaclub]

Felix you're my sort of mechanic! :(

 

So, wreckers for three-wire EB Falcoon sensor to start with... If I can get a narrowband setup working I might broaden it to wideband later.

 

Thanks for that!