MAP, MAF and Alpha-N are the 3 major types of EFI control systems.
The MAF sensor is placed in the air intake ducting between the air cleaner
and the tb. The actual measuring is done be various means but, typically,
a thin heated wire is used inside the MAF housing. The wire is cooled
by the air passing over it. As more air is passed through the sensor,
mor voltage is needed to heat the wire. The computer reads this voltage
and uses it to determine the quantity of air passing through the MAF.
The MAP sensor connects to a vacuum port and reads atmospheric pressure
in the intake manifold. The computer uses this input along with
several others, and compares it to stored data to determine the quantity
of air being ingested by the engine.
Because a MAF sensor measures airflow before it reaches the engine, it is
much less sensitive to engine modifications. Trucks with MAP sensors
often need computer reprogramming to accept engine modifications.
A MAF system are more accurate then MAP system but also more expensive
because the MAF sensor tends to be pricey.
The Alpha-N system is generally used only in racing or on heavily modified
street engines with big cams. Major inputs for Alpha-N are throttle position
and rpm. It was developed because race engines often operate at idle and
part-throttle with very little manifold vacuum. It is the least precise
system
of the three. A MAP sensor can still be used with the Alpha-N but it is
generally used as a barometric pressure sensor to detect attitude changes.
BTW, Ford used MAPs on EFI 5.0L until 1988 then switched to MAF (except in CA
where the switch wasn't made until '89). GM used MAF on TPI-equipped cars
until '89 when it switched to MAP. The LT1 engine used MAP til '94 when
GM returned to MAF.
Bob, Burlington, Ontario
'97 FR CC Sport, 5.2L, 3.55 SG, auto., 15.234 @ 87.26
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