ECU thread
The ECU uses lookup tables to determined the amount of fuel to inject based on MAP/MAF,IAT,RPM readings. It can even have a different table for each gear. This also applies to timing.
It then looks at the O2 sensor to see if the values in its tables achieved the AF ratio it wanted. This does not apply to timing.
So you can't just modify the input (MAF/MAP/IAT) reading because the computer will eventually adjust fuel inj based on the O2 sensor. This amount is called the Long Term Fuel Trim(LTFT) adjustment.
you can't feed a constant signal to the o2 sensor because under acceleration, it expects to see a rich condition, and at cruise, a lean condition.
this explains why when you do a map/maf mod, you see short term gains, but then nothing.
this would also predict that an o2 sensor mod would take some time to take effect.
doing both SHOULD give you immediate and long term results. If you do an O2 sensor mod only, you are not getting the benefit of altered timing.
More later.
1982 MB 300D Turbo Diesel 90%WVO/10%RUG + additives blend. $.50/gal
don't know what MPG is, probly low 20s