1. Fuel filter
The fuel filter removes dirt and impurities from the fuel that is compressed by the fuel pump.
2. Fuel pump filter
The fuel pump filter removes dirt and impurities from the fuel before entering the fuel pump.
If a fuel filter becomes clogged, it will reduce the fuel pressure sent to the injector, causing difficulties with engine starting or poor drivability.
Some fuel pumps are installed on the outside of the fuel tank.
In some models a union bolt or various types of quick connectors are used to connect the fuel line.
Fuel Pump Control
1. Basic operation
The fuel pump only operates when the engine is running. Even when the ignition switch is turned ON, if the engine is not running, the fuel pump will not operate.
(1) Ignition switch ON:
When the ignition switch is in the IG position, the EFI relay turns on.
(2) Ignition switch START:
When the engine cranks, a STA signal (starter signal) is sent to the engine ECU from the ST terminal of the ignition switch. When the STA signal is input into the engine ECU, the engine turns on the transistor and the circuit opening relay is turned on. Then, current is allowed to flow into the fuel pump in order to operate the fuel pump.
(3) Engine cranking/running
At the same time the engine is running, the engine ECU receives the NE signal from the crankshaft position sensor, continuing the transistor on to keep the fuel pump operating.
(4) If engine is stopped:
Even when the ignition switch is ON, if the engine is stopped, the NE signal will no longer be input into the engine ECU, so the engine ECU will turn off the transistor, which turns off the circuit opening relay, causing the fuel pump to stop.
There are some vehicles equipped with a DLC1 as shown at left. When +B terminal and FP terminal of the DLC1 are shorted using an SST with the ignition switch turned ON, the current will flow to the fuel pump without passing through the circuit opening relay to operate the fuel pump. In this way, the inspection of the fuel pressure or pump operation can be performed by forcing the fuel pump to operate.
2. Fuel pump speed control
This control reduce the fuel pump speed to decrease the pump wear and electrical power when much fuel is not required, such as when the engine is running at low speed. When the current flows into the fuel pump through the contact B of the fuel pump control relay and the resistor, the fuel pump operates at low speed. When the engine is cranking, when the engine is running at high speed, or at heavy loads, the engine ECU switches the contact of the fuel pump control relay into A in order to operate the fuel pump at high speed.
ON-OFF control with speed control (by engine ECU and fuel pump ECU)
Some models control the fuel pump speed using the fuel pump ECU instead of the circuit opening relay, fuel pump control relay and resistor. In addition, this type of control also has a fuel pump system diagnostic function. When a malfunction is detected, a signal is sent from the fuel pump ECU to DI terminal of the engine ECU.
3. Fuel pump shut-off system
Some vehicles have a mechanism where the fuel pump control stops the fuel pump in the following conditions to maintain safety.
(1) When an airbag inflatesWhen the SRS driver’s, front passenger’s, or side airbag inflates, the fuel cut-off control stops the fuel pump. When the engine ECU detects an airbag inflation signal from the center airbag sensor assembly, the engine ECU turns off the circuit opening relay to stop the fuel pump operation. After the fuel cut-off control operates, the fuel cut-off control can be cancelled by turning the ignition switch OFF, causing the fuel pump to reoperate.
(2) When the vehicle crashes or rolls overWhen the vehicle crashes, the fuel pump inertia switch will turn off the fuel pump to minimize fuel leakage. The fuel pump inertia switch is located between the fuel pump ECU and the engine ECU. When the ball in the switch moves at a collision, the switch is separated from the contact to turn it OFF and stop the fuel pump operation. After this fuel cut-off operates, push the reset switch to the top to reset the fuel cut-off control, causing the fuel pump to reoperate.
GasolineEngineFuel Injection Methods and Injection Timing
The fuel injection methods are to inject the fuel independently in each cylinder or to simultaneously inject the fuel into all the cylinders. There are also various injection timings, such as injecting at a determined timing or injecting in accordance with the changes in the amount of the intake air or engine speed. The basic fuel injection method and injection timing are as follows. In addition, the larger the injection volume is, the start of the injection timing becomes faster.
1. Independent (Sequential)
Fuel is injected independently for each cylinder once for every two crankshaft rotations.
The fuel is injected for each group once for every two crankshaft rotations.
The fuel is simultaneously injected to the respective cylinders once for each rotation of the crankshaft. The amount of fuel required for combustion is injected over two injections.
1. Fuel filter