I found this neat page about building your own meter. It uses dual LM3915s for extra resolution, but your are on your own to make one- no PC board is available, unless someone wants to draw one up. Also, you get to chose your own sensor.

The only odd thing is the way it's calibrated and how you read it, but it looks like it could be useful.

Pelican Technical Article: Building an In-Dash Air-Fuel Monitor

While this seems simple enough, and the PC board is easy to draw and make, there is some question if we could use it for the S30 engines. The problem is to select the right kind of sensor. The Air-fuel sensors (Lambda sensors) look like they all use a heater, which is controlled by the circuits of a modern ECU. I suppose you could just hook up the heater wires to the 12V power supply and it'll get hot, but you need to maintain a certain temperature, which is the tricky part.

If anyone can simplify the sensor hookup, please let us know.

Edited February 11, 201312 yr by TomoHawk

Do they still need a heater after the engine is warmed up?

I dont' think they do. Lots of O2 sensors are 2-wire. I believe that's the type in my Saturn. They don't really work until they're warmed by the exhaust.

This should get us on the same page.

"Technology for Tuners"Newsletter #3 :: Exhaust Clamp, XD-1, How Wideband Sensors Work, and more!

Modern, affordable accurate wide band AFR is available to masses without having to build our own circuits.

One of the better known systems:

Innovate Motorsports LC-1 and LM-2 WBo2 WideBand o2 Systems Megasquirt Kits / Assembled Engine Management Systems, Wideband o2 Sensor Systems and tuning products - DIYAutoTune.com

there is a big difference in "affordable," as in between $150 and $25. You can make the circuit I posted for about $10 or so, and get a sensor for under $10. So if you could figure out how to get the proper signal from the sensor (with either electric heating or natural exhaust heat) then the DIY way would be great, and you'd get a nice feeling of accomplishment.

So when those gauges are available for $10, I'll buy one.

Edited February 12, 201312 yr by TomoHawk

Since you need to put the sensor in the exhaust gas stream close to the exhaust ports, it looks like you can just ignore all of the heater stuff, right? The heater is basically just for when the engine is cold. A lower-temperature sensor that could be put into the exhaust outlet would be great, but there isn't one.

From the graphic on that web page in post #5, the 'knee' in the curve is pretty much the same for the different temperatures used, so you will have fun calibrating whatever kind of gauge you use.

How about a warning light instead of a gauge you could set for 14:1 or whatever's right for WOT near top RPM ? For me the main use for a wideband would be as a warning for going too lean while racing / testing etc. Without 6 into 2 headers with 2 senders it might not be very useful for tuning SU's.

And how would it be useful on a on a stock efi S30 without other modifications?