AFR / O2 / Lambda Sensors

[djw090]

Some modern cars have a sensor before the cat and one after. I am planning to find a second hand sensor to use on my MGB. Are the before and after sensors essentially the same?

I may get 2 any way so if the before and after sensors are the same I could get them both from the same car. That might make the wiring easier.

[DiDueColpi]

Generally no. The rear sensors are only there to confirm cat operation so they tend to be a simpler sensor.
Some sensors are air/fuel ratio monitors (wide band), some are simple lambda sensors, some heated, some not.
As well some provide a variable voltage , some provide a variable resistance and some provide a variable ground.
What are you connecting them to?

[djw090]

I am connecting them to Megasquirt 1 v2.2. It is being used to control the spark and provide data recording.

The sensors will be used for data logging only. I am only inerested in narrow band at this stage but I had it in mind to use heated ones so they might be 4 wire. To a large extend it depends what is available used/cheap.

[MG four six eight]

David

I highly recommend getting a new one as opposed to a second hand unit. O2 sensors do wear out and can give you false readings and nothing is more frustrating then trying to tune an engine with false imformation. When an O2 sensor is past it's prime, usually the ouput voltage will be lower and they will re-act slowly (poor cross count performance when cycling above/below 14.7 to 1 AFR)
Some of the GM sensors are fairly low cost and work well Mega-Squirt.

Bill