MAF/MAP sensor for those who don't know...
Posted: Wed Oct 24, 2001 10:23 am
--- BASIC AUTOMOTIVE SENSORS 101 ----
LESSON 1: MAF/MAP Sensors
First of all, let's begin with what the two acronyms stand for.
MAF - Mass Airflow
MAP - Manifold Absolute Pressure
These two sensors work in tandem in a turbocharged engine to give the ECU
enough information to get the A/F ratio nearly bang on every rev. Let's
examine how!
Firstly, when the air enters the intake chain, it comes through the air
filter into the MAF. The MAF on most Subarus is the "hot wire" type - a
very thin strip of platinum is heated and suspended in the stream of
air. The temperature of the wire is kept constant - but the amount of air
rushing through the intake causes the temperature of the wire to fluctuate
(or it would fluctuate if it wasn't being kept at a constant temperature) -
the amount of airflow is determined by the extra current required to keep
the wire hot.
This information is useful for non-turbocharged engines and turbocharged
engines alike - but for we turboers, it's *useless* without MAP feedback.
Can you guess why?
That's right, the MAP sensor tells us how good a job our turbocharger is
doing (which is important). The airflow (MAF) multiplied by the pressure
(MAP) gives us an approximate volume of air.
This allows us to calculate the required amount of fuel (based on
precalculated amounts of airtemp increase due to compression) required to
make the reaction in the cylinder a quick expansion rather than a
engine-frying explosion.
NOW, that being said... a turbocharged engine will run fairly well on the
MAP alone, and a naturally-aspirated motor will run fairly well without the
MAF, because the airflow at a given air pressure (or RPM in the NA motor)
is fairly predictable. The reason they both run like shit is simple:
without the MAF, the ECU reverts to precalculated values.
Sometimes they'll be lean, sometimes rich.
Scary, scary folks.
Hopefully that's cleared it up for a few of you.
-Matt
------------------------ ---------------------~-->
Monitoring Service trial
http://us.click.yahoo.com/Gi0tnD/bQ8CAA ... /XoTolB/TM
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LESSON 1: MAF/MAP Sensors
First of all, let's begin with what the two acronyms stand for.
MAF - Mass Airflow
MAP - Manifold Absolute Pressure
These two sensors work in tandem in a turbocharged engine to give the ECU
enough information to get the A/F ratio nearly bang on every rev. Let's
examine how!
Firstly, when the air enters the intake chain, it comes through the air
filter into the MAF. The MAF on most Subarus is the "hot wire" type - a
very thin strip of platinum is heated and suspended in the stream of
air. The temperature of the wire is kept constant - but the amount of air
rushing through the intake causes the temperature of the wire to fluctuate
(or it would fluctuate if it wasn't being kept at a constant temperature) -
the amount of airflow is determined by the extra current required to keep
the wire hot.
This information is useful for non-turbocharged engines and turbocharged
engines alike - but for we turboers, it's *useless* without MAP feedback.
Can you guess why?
That's right, the MAP sensor tells us how good a job our turbocharger is
doing (which is important). The airflow (MAF) multiplied by the pressure
(MAP) gives us an approximate volume of air.
This allows us to calculate the required amount of fuel (based on
precalculated amounts of airtemp increase due to compression) required to
make the reaction in the cylinder a quick expansion rather than a
engine-frying explosion.
NOW, that being said... a turbocharged engine will run fairly well on the
MAP alone, and a naturally-aspirated motor will run fairly well without the
MAF, because the airflow at a given air pressure (or RPM in the NA motor)
is fairly predictable. The reason they both run like shit is simple:
without the MAF, the ECU reverts to precalculated values.
Sometimes they'll be lean, sometimes rich.
Scary, scary folks.
Hopefully that's cleared it up for a few of you.
-Matt
------------------------ ---------------------~-->
Monitoring Service trial
http://us.click.yahoo.com/Gi0tnD/bQ8CAA ... /XoTolB/TM
---------------------------------------------------------------------~->
To unsubscribe from this group, please send an email to:
BC-BFLegacyWorks-unsubscribe@egroups.com