i have seen the expensive portable A/F ratio gauges and i have seen the indash gauges, any Doc Brown types build their own on a Kool-Aid budget??

Use a narrow-band O2 sensor and a digital voltmeter.............

Here's a graph of the approx millivolts vs A/F

http://www.conservatory.com/vw/manuals_ ... ETL-18.GIF

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

i was wanting something that i could build and use as a portable tool, if i was going to fit an O2 sensor i would just mount an LED gauge under the dash..

Hmmmm. JDS brings up a good thought process. I can't help but wonder if a guy couldn't use a heated O2 sensor and a narrow-band LED guage in a hand-held housing. Have long enough leads to hook up the 12v + and - to the battery, and stuff the O2 sensor into the tailpipe. I can't say how accurate the reading might be that far back, but it could be checked against a known signal in a tuned vehicle.

Roger

You would have to use a heated O2 sensor and make sure you have NO LEAKS in your exhaust system at all. Then it might work.

Lou

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Home of Slant6-powered fun machines since 1988

For about $30 at some pawnshop you might be able to find one of those old Exhaust analyzers that clips into the end of the tailpipe, and runs off the battery...I have one my grandfather left me...it's not as accurate as welding the bung in the pipe close to the manifold, wiring the gauge in, and tuning things up...

-D.Idiot

You have to fit an o2 sensor somewhere, regardless of wether you build your own gauge or purchase one. The gauge however is a simple voltmeter so you can use a digital vom if you have one as gauge replacement.

Edelbrock and others make all in one kits with gauge and sensor etc. Autometer, stewart warner make the fancier gauges that you can mate with your own sensor. They probably sell their own branded sensor as well.

Even unheated o2's, left at back of pipe for a few seconds will get too hot to touch so the "all in one" housing is out of the question.

Innovate motorsports makes a bracket with clamp to mount a sensor at back of pipe. Since sensor dimensions are the same wide or narrow band you can use the bracket for cheaper narrowband sensors, but I'm with Roger on this one I don't think narrowbands were made to use that far back. All the innovate motorsports stuffs is wideband.

I have their LC-1 kit in my car - its a slick unit, has 2 fully programmable outputs, one sent to the efi controller and one to indash gauge. Not exactly kool-aid budget though, $200 for sensor/controller kit (comes with weld in bung, tailpipe bracket separate).

i think that i will just end up using one of the mounted gauges and run an O2 sensor after the manifold. there are quite a few brands and styles floating aroung, anybody have a fav or a horror story? i think the led style looks pretty sharp, but of course i will be mounting this down low not to attract attention, i'm using it as a tool, not for styling!

JDS....That's what I did, right in the panel of my race car. It makes a great tuning tool, along with plug readings, but I figure it will give me a heads-up, should something go south in the carb on the motor.

I used a Stewart-Warner from Summit, and it's an LED "sweep" guage. Three wires, 12V+, 12V-, and the O2 sensor hookup. The guage was about $52, and the sensor came out of a GM product at a local boneyard. (Make sure you get both the wiring connector "halves".)
I understand that Nordskog is now making a needle-sweep guage for air/fuel ratio for about $55, and I tried to get that one from Summit, but was told it would be a three-week lead time. Couldn't wait that long.

Roger

I bought a colored LED bar graph A/F gauge from JCWhitney and connected it to a factory O2 sensor - it seems to work fine. I often see it goes offscale toward lean, but everything seems to work fine. I think it ran ~$36.

Why is that so important?

If outside air gets into the system, the A/F ratio will look leaner than it actually is

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Even with the pressure of exhaust gases?

Pressure isn't constant, and can actually go below atmospheric in the pipe.

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

Of course, a standard narrow band oxygen sensor can only be used to determine three things:

1. when you are at stoichiometric A/F (14.64:1)
2. when you are richer than stoich
3. when you are leaner than stoich

You will not be able to determine your actual A/F beyond this. As long as these limitations are acceptable to you, then any display using a narrow band is OK.

Mitch