Iv been strugeling for a while now to work out why my ecu is running with a shift of 15-25% rich ( not measures this is the computers compensation amount ), iv logged dats rom the ecu, the maf readings are reasonable ( had it off, it looks like it was changed by the previous owner and is new and clean) and changes responsivly with speed and load, the O2 sensor ( of which there is only 1, 1998 mk1 focus) reads in a range of 0-1.2 and jumps around nicely, no damage to wiring. There is also excessive soot building up on spark plugs and the like ( brand new plugs, black very quickly ) but no black smoke from the exhaust yet.the MPG is steady but lower Than I would expect / want.

Anyone get any ideas?