Hello folk.
My car is struggling with emissions at MOT time. 
Would fitting an aftermarket ECU allow the car to be tuned to pass the emissions test?
Any help is appreciated.
Many thanks.
Guy
My first reaction is that’s both expensive and not the best way to address the problem. Of course a healthy NB passes emissions using its stock ECU with no problem, and if yours doesn’t then something needs addressing but it’s really not likely to be the ECU.
Do you have any previous printouts of the actual emission numbers? They often provide clues.
Hello Martin, I agree completely that an ECU is an expensive solution but I’m exploring all options to keep her on the road.
I should clarify that the emissions test was incomplete this year because she began to overheat before the second run could be finished.
Last year she scraped through. The first CO2 reading was 1.272 (max 0.300). The second run was 0.295 (max 0.300).
Before last years MOT (less than 5K miles ago) she had new plugs, HT leads, air cleaner and an Italian tune up on the way to the testing station.
I shall book her in again this week and keep my fingers, eyes, toes and legs crossed.
I think you mean CO reading. My 1998 NB can be difficult and needs to be really hot but also the exhaust system must be free from leaks, even a faint blow will cause a fail. My car is still on the original cat and Lambda sensor after 129,000 miles
Yes, exhaust leaks between the engine and the O2 sensor can upset its readings and increase CO emissions. Worth having a good look for typical white or black powdery marks at any joins.
Injector cleaner might help, if one is a bit clogged and the fuelling isn’t even across all 4 cylinders, or if the spray isn’t very fine droplets so the combustion doesn’t complete.
Definitely keep a note of the CO, HC and Lambda readings as they can all tell you something.