EFI - Fuel Syste
m
2
. FUEL PUMP CONTRO
L
The fuel pump in a vehicle equipped with an EFI
engine operates only when the engine is
running
. This is to prevent fuel from being
pumped to the engine when the ignition switch
is on but the engine is stopped
.
The following types of fuel pump control are in
use at present
:
On-off
contro
l
Fuel pump
control
method
L
I On-of
f
L control
with
speed
control
By Engine EC
U
By fuel
pump switc
h
By Engine ECU,
fuel pump control
relay and resistor
By Engine ECU
and fuel pump
EC
U
ON-OFF CONTROL (BY ENGINE ECU)
*
1)
Engine crankin
g
When the engine is cranking, current flows from
the IG terminal of the ignition switch to the Li
coil of the EFI main relay, turning the relay on
.
At the same time, current flows from the ST
terminal of the ignition switch to the L3 coil of
the circuit-opening relay, turning it on to operate
the fuel pump
.
Battery
The starter operates next and the
engine begins
to crank,
at which point
the Engine
ECU receives
an NE signal
. This signal causes the transistor
inside the Engine
ECU to go on,
and current
therefore
flows to the L2 coil of the circuit-
opening relay
.
~2 Engine
starte
d
After the engine sta
rt
s and the ignition switch is
returned from
the START
position
(
ST terminal)
to the ON position (IG terminal), current flowing
to the
L3
coil of the circuit-opening relay is cut
off
. However, current continues to flow to the L
:
coil, while the engine is running, due to the
transistor inside the Engine ECU being on
. As a
result, the circuit-opening relay stays on,
allowing the fuel pump to continue operating
.
($)
Engine stoppe
d
When the engine stops, the NE signal to the
Engine ECU stops
. This turns off the transistor,
thereby cutting off the flow of current to the L2
coil of the circuit-opening relay
. As a result, the
circuit-opening relay turns off, turning off the
fuel pump
.
D-EFI systems and L-type EFI with optical Kar-
man vortex type air flow meter or hot-wire
type air flow meter
.
55
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