I have no idea what VW did to cheat the USA rolling road NOX tests but I know what can decrease NOX values in a DTI engine combustion chamber and they can all cause lower efficiency, lower performance, poor drivability and possible engine damage if activated on the road.
1. Injecting excess fuel with lower air/oxygen into the combustion chamber can = diesel knock and possible piston, conrod and bearing damage especially under load.
2. Opening the EGR valve/s early and/or over a longer time period and/or engine temperature range.
3. Increasing exhaust valve overlap using the VVT to leave exhaust gasses in the combustion chamber to lower combustion tempertures on the next power stoke.
VW may have used all the above or not to pass the USA rolling road emission tests and as I recall somewhere a few engines were for whatever reason run in test mode on the road and unfortunately destroyed themselves
And not all the engines affected just require a re-map, which means that some will need other electronic and/or mechanical update components in order to function over the possible longer time spans as detailed above, which may also include the need for more efficient DPF's or AdBlue cats on some engines.
“If you see a gap and don't go for it, you are no longer a racing driver”
Jaguar x-Type 2.2D S Saloon 2006 149k Black. First Jaguar. No modifications.
Maintenance: Sills and rear running gear repaint. Rear chassis and body under seal. Headlight revamp & T Cut. Lubricate clutch pedal, hinges and joints.
Items replaced: LH drive shaft and bearing. Aux belt, tensioners, Crank pulley. Reverse switch. A/C compressor. Front EGR hoses. Thermostats. RH Splash guard.