MAF vs MAP

[Michael T. Kasimirsky]

On Thu, 26 Feb 1998, Shannen Durphey wrote:


> >   Did that 96 Corsica have both a MAF, and MAP?.
> Yes.   Seems that most of the OBDII cars are like this.

I believe this is a requirement of OBDII.  The protocol requires that 
there be logic for detecting failed (or failing) sensors.  For the MAF 
sensor, the PCM uses MAP and RPM to do a speed-density calculation that 
it compares to the MAF input.  If the numbers aren't close, it sets an 
error code.  OBDII is chock full of these little tidbits, for example, 
coolant temp and intake are temp sensors are cross-checked on a cold 
start, etc., etc.  All of it is to keep the car from going outside the 
emissions specifications.

Michael T. Kasimirsky       ---->              mtk at tmc.astm.cmri.cmu.edu
Days:    Staff Engineer                     or mk4u at andrew.cmu.edu
         ASTM Test Monitoring Center           Phi Gamma Delta,
Nights:  1992 Suzuki GSX-R750 Pilot            NRA Life Member, AMA Member
         1990 Yamaha FZR400 Superbike Racer    DoD #1848
         1991 Suzuki GSF400 Bandit Mechanic    WERA Novice #22