Tuning Seicento sporting 1.1 mpi 2002 STFT

[dx90]

If my short term fuel trim was higher than 25% would it still pass the MOT emissions test? Mine did. Maybe I have a problem with the software I'm using. What do you think?

Thanks

 

[dx90]

My STFT is -34% using Scanxl Pro. Yet it still passed its emission test for the MOT.

Is it possible for the ECU to alter all the settings enough for it to pass the emissions test?

Thanks

 

[woj]

I am not sure why you bothered about this... STFT does not mean that the currently running mixture is bad, it means that it had to be corrected by the factor of X% to be OK, which it is at the moment. The only bad thing happens when the FT (short or long term, does not matter) reaches its limit, which for the 1.1 MPI ECU is +/- 50% if my memory serves me right, but I'd have to check.

The question you should be asking yourself is why the STFT is so large and whether that indicates an approaching problem with your fuel system. It means that the ECU is over-fuelling by default. It's probably not caused by a faulty lambda, because then the emissions would be off. But my experience with the 1.1 maps tells me that 34% might as well be a figure still in limits for an otherwise healthy engine and sensors.