EGO sensor/meter

[Jari Porhio]

Andris wrote:

> on the testbench. There was a note in the instructions that I should
> ground it only at the o2 sensor. What is the best way to ground it

 Whatever is easy to do. With a regular exhaust system, you can weld a
little loop to the exhaust pipe. Or just tighten the wire/connector
between the sensor and the exhaust.

> I got the o2 meter mounted now, and grounded it on one of my accessory
> circuits. The voltage difference is around .2 volts, since that is the
> LED reading w/o the engine running. The only problem is that the meter
> doesn't work! When the engine is running, the led lights from 2 to 3.

 Looks like your input is open, i.e. the sensor is not connected
properly.  The meter wants to light about two or three LEDs when the
input is floating.

 Make sure you know what sort of sensor you do have, what are the
signal and ground wires. If there is no ground wire, the sensor body
is the ground. If your signal wire is connected properly, and since
you grounded to something else than the exhaust, your exhaust could be
floating off the car ground altogether.

 An EGO sensor produces a low-level, relatively high-impedance voltage
over its signal wire and body/ground wire. This is the signal you want
to feed for the meter or whatever circuit is there. The power voltage
for the meter isn't that important. Of course if the power fluctuates
referenced to the ground, you will get spikes (like when you shut off 
the engine).

 So, if your exhaust system is close to the car/engine/charging/
battery ground, you can get away with three wires: signal from the
sensor, ground from the sensor and power from ignition switch. You can
add another ground for the power, but sometimes something funny could
happen (I don't know). Basicly you have added a ground loop.


Bruce wrote:

> stated that the O2 sensor puts out a roughly linear voltage as one
> mucks with the A/F ratio. Others have stated that the O2 sensor
> acts like a hard "switch" at stoichiometric, producing voltage

> Which is it? OEM boxes appear to treat the signal as a switch, but I see

 Just try one and you will immediately see. If you don't expect much,
it will provide you some useful information. It just doesn't tell you
any accurate numbers, and it can be misleading sometimes (temperature,
humidity, electrical noise, engine misfires, aging, contamination).

__________________________________________________________________________
 Jari Porhio   http://www.iki.fi/eppu/