What readings can I expect from a diesel exhaust?
The exhaust gas readings from diesel exhausts very widely depending on the type of engine management system.
A five gas analyser will accurately measure the following gases: Oxygen, Carbon Dioxide, Carbon Monoxide and Oxides of Nitrogen (NOx).
It will also measure Hydrocarbons (HC) but because the analyser's response is optimised for hexane, the HC readings from a diesel's exhaust will be inaccurate (very low maybe only 5% or so of true HC reading) and should be discounted.
Note: To create representative levels of NOx, the engine must be under load.
Examples (not necessarily typical, just random measurements):
Normally aspirated diesel engine at idle:
Turbo diesel engine at idle: