Ecotek's CB-26P has been discussed many many times on these NGs, with most people of the opinion they don't work but a few fans convinced that they do. Ecotek have now (finally!) carried out a set of scientific rolling-road economy and emissions tests on relatively modern cars
Yes, that's right, a ONE per cent improvement in fuel consumption - well within the bounds of experimental error, and even if real, insignificant in terms of savings versus cost of fitting. Although the cars tested were from 2001, it seems highly likely that the results would apply equally to any lambda-controlled car; that is to say, anything sold in the UK since 1993.
So it looks like we were right all along! (Anti-triumphalist note: all credit to Ecotek for releasing these results and not just burying them...)
There's a full analysis at