Hi Ian

I too shared your reservations especially with the advent of OBD and O2 sensor.

I fitted a CEV to my 98 Honda having first videoed not only the emissions but the Lambda switch, which was rather lethargic.
In attendance was Dr Terry O'Neill PhD MBA MSc Chartered Engineer(MIEE) and Chartered Physicist(MIoP).

Having connected the device, started the engine and ran on fast idle for a short whilst monitoring the Lambda.
Entering closed loop the the count was much faster as if we had fitted a new sensor.
Quickly we hooked up my Lucas 5gas inc NOX Analyser (I'm sure Darren Bamford could vouch for this splendid machine) and were surprised how quickly the emissions dropped. The drop in oxygen levels and rise in carbon dioxide together with steadily reducing CO & HC figures showed how more efficient the engine had become.

The engine was noticeable smoother tacho being rock solid at idle.

We have since fitted a CEV on my Son's Skoda Superb,the works Berlingo diesel and Terry's (although recently passing a MOT smoke test) 1990 Merc engined Motor home and his son's Mondeo 2.0 TDCi.
All giving reduced smoke results. Also I have the printout's of former tests showing a drop of 50% to 82.5%.

I'm sure if asked the independent MOT garages who who did the tests,would confirm the device definitely works.

We have yet to fit one to a OBD11 petrol with (pre & after) O2 sensors, which Terry thinks could be a problem.

Regards Derek