Homemade Air/Fuel meter

Gannon · Post by **Gannon** » Sat Jul 22, 2006 2:06 pm

Feeling creative thismorning, I ran two wires to the exhaust pipe Y join/cat converter, one is connected to the o2 sensor and the other is just connected to the body.
At the other end, is my multimeter set on millivolts range.

I discovered that at idle, the o2 sendor produces around 70-250 mV.
At full throttle under load, as high as 700mV
At cruise, it varies anywhere between 200 - 600mV
On deacceleration, it can drop down to -150mV ...Yes minus 150mV

I tested to see if this was lean by unplugging a vac line, and yes, it showed -170mV

This is a carburettored engine, and i expected it to show rich mixtures (indicated by positive voltages)

Im curious to see how a mpfi or turbo car would show

All expressions and coments are welcome

Gannon

subanator · Post by **subanator** » Sat Jul 22, 2006 11:20 pm

I was doing this also to faultfind my EA82T problems running lean. I ran a pair of wires back inside to my meter, and watched it while driving.

Can do the same for the hotwire airflow sensor reading 1-5V

But as that O2 sensor is a narrow band sensor, you dont really get a true indication of mixture due to their design. Thats why a 4 wire one is prefered as its wide band sensor, but outputs differently and requires the equvilent ECU to read it.

The narrow band O2 reading fluctuates even at steady throttle, as the ECU is "averaging" the mixtuer via closed loop. On a turbo car on boost, the signal goes out of range of the sensor and the ECU ignores the value and goes open loop control via its fuel mapping.

If you want to make a air-fuel meter, Jaycar have a kit for a 4 wire, but needs to be calibrated against another. I may give this one a go myself.

Gannon · Post by **Gannon** » Sun Jul 23, 2006 7:26 am

I know that the reading are rough, but it still gives you an idea of what is happening,.. i was glad that i was able to get a reading ie. without a compuer or such do analise it

What were your readings like, did they vary much from mine?
Did it show you it was running lean?

Yeah i was looking at a jaycar kit myself, but im pretty sure it was for a single wire, narrow band sensor. only about $15

If your car is a 4 plug ecu/hot wire type, im pretty sure that it only runs in open loop mode when it is cold, until the sensor warms up.
The 4 plug ecu has no boost sensor so there is nothing to tell it it is on boost.

Gannon

fredsub · Post by **fredsub** » Sun Jul 23, 2006 7:55 am

I remember that sensor connection thing on the old cat, but I thought it was probably a temp sensor, thermocouple perhaps not a O2 sensor.
The bung for it too, is fairly common size for temp sensor too, and not O2
I never could get it out.......

subanator · Post by **subanator** » Mon Jul 24, 2006 11:25 pm

Suparoo, my readings were pretty similar, would either go neg or zero when lean. Apparent range expected lean 0.2 - 0.9V being rich.

Measuring the O2 sensor was a indicator only and by no means accurate, as I found out later when a tuner measured mine as A-F ratio meter, it was super lean being as low as 16:1, a problem now corrected.

The Jaycar kit can be added to include a dash mounted LED mixture panel, just need a better 02 sensor like a 4 wire, having a different reactive metal to sense with and a heater to aid reading for cold start/running.