MAF vs SD for dummies
Lead Driver
Joined: Nov 2002
Posts: 9,557
Likes: 44
From: Concord, NC
A common misconception is that MAF computers don't have calibration tables, which is untrue. The difference between mass air and speed density is simply the method used to determine engine load for fueling purposes (possibly timing as well, depending on the computer). Both mass air and speed density have a table with load on one axis, rpm on the other axis, and fuel pulse width as the table values. The mass air computer uses input from the mass air sensor as the load axis, while speed density uses manifold pressure. You could probably call mass air "speed mass" if you wanted and it would be correct.
The reason that mass air can "adapt" to changes better than speed density is that fueling, for the most part, is based on the amount of air entering the engine. If the air flow is increased, the computer simply references a higher load line in the fuel table. Conversely, the reason that speed density cannot adapt as well is that fuel is determined by manifold absolute pressure (air density), such that if the volumetric efficiency is changed (more air flow for the same manifold pressure), the computer is still referencing the same table value as before, but the fuel value is now incorrect.
The reason that mass air can "adapt" to changes better than speed density is that fueling, for the most part, is based on the amount of air entering the engine. If the air flow is increased, the computer simply references a higher load line in the fuel table. Conversely, the reason that speed density cannot adapt as well is that fuel is determined by manifold absolute pressure (air density), such that if the volumetric efficiency is changed (more air flow for the same manifold pressure), the computer is still referencing the same table value as before, but the fuel value is now incorrect.
Postmaster
Joined: Jul 2006
Posts: 3,978
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From: Central PA
Originally Posted by 17fordguy
what years were sd and what years were maf?
94 F150 auto only (well anywhere but Cally) Most I foundr e4od OBDI
Sequential
95 F150 have seen 300 -6 with Maf . auto also . OBDI sequentail
96 F150 About everything was MAF.(althought I never saw a 351 Or F250 up in any year that was not supposed to be a Cally truck that had MAF . ) And switched to OBDII
The F250 and up stayed OBDI and have not seem any with MAF .
