i have read lots of threads but with no joy do you need the lambda sensor i know you would need it for mots but thats about it or is it

 

yes - you need it - on the low end of revs operation, its a closed loop feedback system.

 

It's an essential sensor input for the ECU and in fact the only sure fire way that the ECU knows what the mixture is like. Take it out and it's like having central heating in your house without a thermostat.

 

Without it the ECU will run Open Loop fuelling direct from the fuel base map all of the time rather then use the Lambda sensor for low rpm/load i.e below 3,000rpm and 0psi boost. Above that it is redundant.

If the map is anygood (which most standard maps are and well remapped aftermarket ECU should be) then the fuelling will be fine but may not be quite tight enough to get through an emissions test.

When I first put a wideband sensor into mine (with the narrowband disconnected), running a standard ECU the open loop fuelling was very close to 14.7AFR, so close infact that you would of thought it was running closed loop with Lambda feedback.

With my Apexi setup, it runs near the same with or without the lambda switched on.