Cameron Apparently the MAF and MAP are not the same. I copied a writeup from
http://www.racer-x.f2s.com/proc/tpi2.htm which is shown below. It appears that the MAP only measures the air pressure - partially for the vacuum caused by the engine "sucking" in the air and the engine system computer uses a "memorized" program to guess at the air flow and other parameters measured by a MAF. I have not yet found anything about a system having both a MAF and MAP. The only advantage of the MAP (as mentioned below) is that it is less of a hinderance to air flow rate compared to a MAF. It is my guess that a MAP is less expensive than a MAF and motor vehicle companies are famous for working very hard to cut manufacturing costs as much as possible.
I am putting quote marks around the below stuff I borrowed from that
http://www.racer-x.f2s.com web site.
"3. The Mass Air Flow Sensor (MAF)
The ECM needs to know how much air is being taken in so that it can perform a variety of engine
management functions. Until 1989 GM used the Mass Air Flow sensor (MAF) for this purpose. While in
terms of function it is a nearly perfect sensor, in terms of performance it is a hindrance to air flow, and
therefore just begging to be hot rodded. 305 and 350 engines used the Bosch design MAF almost
exclusively, which is capable of flowing a measly 529 cfm. With some smart modifications, this number can
quite easily jump to over 700 cfm. For these procedures, click HERE. A word of caution, though: MAFs
are pretty sensitive, but more importantly, they are pretty expensive - up to $400 or more for a new one
(rebuilt units are available also). Be ready for the possibility that you will botch the job and have to pony up
the dough for another one. For the faint of heart, there are companies such as TPIS that will sell you a
modified one, or modify yours for you.
Starting in 1990, GM began using a Speed Density system. This system uses a Manifold Absolute
Pressure (MAP) sensor in place of the MAF. The MAP differs from the MAF in that it measures engine
load (using manifold vacuum) instead of intake air mass. The speed density system has the advantages of
reliability and zero intake restriction, but the MAP sensor is a far more limited sensor than the MAF, and
therefore less flexible; you can modify your MAF engine to the hilt, and the MAF will go about happily
reporting air mass, temperature, humidity, and pressure to the ECM without a complaint. The MAP sensor
on the other hand delivers only intake manifold vacuum values, and the ECM must rely on "fuel maps"
stored in memory to properly calibrate engine function based on the MAP readings, along with the input
from other sensors. What this means is that major engine modifications on speed density systems
generally require a revised PROM with the new fuel maps in memory.
Despite it's shortcomings, speed density systems are generally the choice for most high performance
systems. It is possible to convert your MAF system to the speed density type, but this switch is expensive
- it can approach $1000 for the new harness, MAP sensor, air ducting, and PROM. If you decide to make
this move, make sure that you really like the combination that you settle on - remember, modifications such
as camshaft changes will necessitate burning a new PROM so that the ECM can keep up."
Some other web sites on MAPs are:
http://www.racer-x.f2s/com/proc/maplearn.htm
http://www.autoclassroom.com/straight/sensor3.html
Mike in Seattle 91XLT 4x4
[Edited by MikeP on 12-26-2000 at 07:46 AM]
j/k. I'll keep y'all posted!
