MAF vs. Speed Density
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Freshman User
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MAF vs. Speed Density
I have read all these things on this website about Mass air flow and speed density, what is the difference between the two? I have a 1992 F-250 4x4 with a 351, which do i have MAF or Speed Density?
Lead Driver
Joined: Nov 2002
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From: Concord, NC
Your truck has speed density. What this means is that the amount of fuel injected is determined primarily from a combination of engine rpm (speed) and manifold pressure (air density). Mass air flow determines the proper amount of fuel based on engine rpm and the actual mass flow of air entering the engine, as determined by a mass air meter.
Posting Guru
Joined: Mar 2002
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From: Boise, Idaho
My 86 Mustang 5.0 is a Speed Density SEFI engine. No, SD does not mean it's batch fire.
A Mass Air meter is a hot wire. The electrical resistance of the wire varies with the temperature of the wire. As air passes over the wire, the air cools the wire and changes its resistance. More air cools the wire more.
A Mass Air meter is a hot wire. The electrical resistance of the wire varies with the temperature of the wire. As air passes over the wire, the air cools the wire and changes its resistance. More air cools the wire more.
Lead Driver
Joined: Nov 2002
Posts: 9,555
Likes: 40
From: Concord, NC
Paul's right. While these trucks are batch fired on the speed density versions, the injection method is independent of whether the fueling is speed density or mass air based. One could program a computer to use mass air and batch fire the injectors if that was desired.
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