The terms MAF scaling vs MAF tuning are open to interpretation. This article will covers the MoviChip interpretation.
We scale the MAF when we have changed something in the inlet tract. We have done something that alters the way the MAF reads the air. We need to scale the MAF sensor to compensate for these changes so we get accurate data going to the ECU.
Changes to the intact tract could include changing the diameter of the MAF housing, changing the MAF sensor itself, fitting a CAI which moves the MAF, either locating it a different distance from bends and/or changing the diameter of the tube where it is mounted. Changing the tube itself eg from corrugated to smooth eg from rubber to metal could also affect the accuracy of the MAF sensor signal.
How do we know if MAF scaling is required?
Fuel trims, short term and long term, will let us know if the ECU is having to compensate for incorrect readings. If the fuel trim is plus 10% and the only change has been to the MAF sensor (as detailed above) then it’s a fair assumption we need to scale the MAF sensor signal. Ideally we want the fuel trims to be 0.
MAF tuning is when we want to adjust the fuelling of our engine because we have changed the camshafts, changed the injectors, changed/removed the cat, fitted different headers.
The MAF sensor is still reading the air in the same way, the sensor reading is still accurate but the signal the MAF sensor sends to the ECU does not give the AFR we need.
In this case we need to “tune” the MAF sensor signal to get the fuelling we need.
Generally, engines with MAF sensors can adapt to breathing mods. These mods will alter the amount of air entering the engine and the ECU will know this and adapt because it is getting the MAF sensor signal.
However on cars with a narrowband lambda sensor, this sensor will only be affecting the fuelling when the car is in a steady cruise state or close to a cruise state. In full throttle/big load conditions the engine will be working in open loop ie not taking a reading from the lambda sensor. In these circumstances we can tune the MAF sensor signal to get the AFRs we need.
Amount of adjustment – Things to bear in mind
The amount of adjustment/the amount we can tune the MAF will vary from car to car. Some ECUs will allow big adjustments to the MAF signal, maybe up to +/- 50% or more. Others won’t.
In other words, on some cars MAF tuning can get the results we need, on others it won’t
There are also consequences to “tuning” the MAF sensor signal. Read about them here
Cars with Wideband Lambda Sensors
If we are scaling the MAF, wideband lambda sensors pose no issues. When we scale the MAF we are just making the signal accurate. We are not trying to adjust the tune of the engine ie adding more or less fuel.
However when the car is constantly looking at the AFR, piggyback units which alter the MAF sensor signal to change the AFRs will probably be of limited use. In these cases we either need to go into the car’s ECU itself and alter the AFR targets or we need to use a device which can control the fuel injectors completely independently of the car’s ECU.
Here is an excellent video by Motive Video which covers the potential MAF sensor signal issues when we fit a cold air intake