Air Flow Meter; Vane Type - Toyota COMPUTER-CONTROLLED SYSTEM Training Manual

®
NOTE
ELECTRONIC CONTROL SYSTEM - Manifold Pressure Sensor (Vacuum Sensor),
Air Flow Mete r
The manifold pressure sensor uses the
vacuum in the vacuum chamber that is built
into it . The vacuum in this chamber is close to
a perfect vacuum, and is not influenced by the
changes in atmospheric pressure that occur
due to changes in altitude .
The manifold pressure sensor compares the
intake manifold pressure to this vacuum, and
outputs a PIM signal which is not influenced
by changes in atmospheric pressure .
This permits the ECU to keep the air-fuel ratio
at the optimal level even at high altitudes .
AIR FLOW METE R
The air flow meter is used with L-type EFI for
sensing the intake air volume .
In L-type EFI, this is one of the most important
sensors . The intake air volume signal is used t o
calculate the basic injection duration
ignition advance angle .
The following three types of air flow
used :
Vane type
Volume air flow -F
meter
and basi c
meter ar e
L
Optical Karman vortex typ e
Mass air flow _ Hot-wire type
mete r
Pe
rf
ect
Atmospheri c
vacuum pressur e
p 101 .3 200 kPa
(0, 0) (760, 29 .9) (1500, 59 .1) (mmHg,
. . . . . . . . .
in .Hg)
Absolute pressur e
101 .3
(760, 29 .9 )
Vacuum
0
(0, 0 )
Vacuum
0
(0, 0 )
(sea level )
(high altitude)
OHP 10
1 . VANE TYP E
There are two types of vane type air flow meter .
These differ in the nature of their electrical
circuitry, but the components for the two types
are the same .
This type of air flow meter is composed of many
components, as shown in the following
illustration :
Potentiomete r
Slide r
Return spring
Idle mixture
adjusting scre w
Bypass passag e
Measuring plate
OHP 1 1
18