Wideband O2 sensor versus MOT

[DaveEFI]

How accurate is the average wideband system at idle versus the test equipment they use at MOT time?

[mgbv8]

My Zeitronix wideband is within 2% of the sensor that Martin uses at Marlin Motor Engineers when my car is on the Dyno ?? But who can tell which sensor is wrong???

[DEVONMAN]

As the MOT sensor is placed at the end of the exhaust pipe, any leaks etc may affect the readings more so than a lambda placed further up the system.

I expect all types of gas analysis equipment would vary slightly as they have to be matched to the sensor/pickup in the first place and certain types may need recalibrated over time.

With 1 volt systems, iffy wiring connections could affect the results.

[stevieturbo]

How accurate is the average wideband system at idle versus the test equipment they use at MOT time?

They are measuring totally different things....so not really comparable in that sense.

[DaveEFI]

How accurate is the average wideband system at idle versus the test equipment they use at MOT time?

They are measuring totally different things....so not really comparable in that sense.

I found some tables that gave the C0 output you'd expect at a given AFR.
Using those, the readings I get at idle are very different from the MOT one for CO. So just wondered why.

[stevieturbo]

How accurate is the average wideband system at idle versus the test equipment they use at MOT time?

They are measuring totally different things....so not really comparable in that sense.

I found some tables that gave the C0 output you'd expect at a given AFR.
Using those, the readings I get at idle are very different from the MOT one for CO. So just wondered why.

expect....but maybe not.

Wideband isnt reading HCC, CO, CO2, O2 or any of those things....and those readings can be skewed by air leaks, misfires etc etc, as of course can wideband readings.

So there's just lots of potential for what they should read...as to what they actually do read.
But with a gas analysers it's much easier to see where any problem may lie, because you've got a good picture of all the gases coming out. With a wideband, you need to be fairly sure everything is healthy for it to be usable for guessing CO emissions

A very very tiny air leak can have a big impact...but you'd spot this a mile off from a high O2 reading on the gas analyser, likewise lambda would then appear lean, but the car could actually be rich. CO would tell you if this is really the case or not

Widebands just dont have access to all that info.