®
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 screw
Bypass passag
e
Measuring plate
OHP 1
1
18
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