The fuel is taken from the fuel tank by the fuel pump and sprayed under pressure by an injector. The fuel pressure in the fuel line must be regulated to maintain stable fuel injection by the pressure regulator and pulsation damper.
Main components
Fuel tank
Fuel pump assembly
Fuel pump
Fuel pump filter
Fuel filter
Pressure regulator
Delivery pipe
Injector
Pulsation damper
Fuel Pump and Pressure regulator
The fuel pump is installed in the fuel tank and is integrated with the fuel filter, pressure regulator, fuel sender gauge, etc. The pump impeller is turned by the motor to compress the fuel. The check valve closes when the fuel pump is stopped to maintain the pressure in the fuel line and make it easier to restart the engine. If there is no residual pressure, vapor lock can easily occur at high temperatures, making restarting difficult. The relief valve opens when the pressure on the outlet side becomes too high in order to prevent the fuel pressure from becoming too high.
The pressure regulator controls the fuel pressure to the injector at 324 kPa (3.3 kgf/cm2). (Values may differ depending on engine models) In addition, the pressure regulator maintains the residual pressure in the fuel line in the same way as the fuel pump check valve. There are two types of fuel regulation methods.
1. Type 1
This type controls the fuel pressure at a constant pressure. When the fuel pressure exceeds the force of the pressure regulator’s spring, the valve opens to return fuel to the fuel tank and regulate the pressure.
HINT:
The injection port of the injector is applied the vacuum by the manifold vacuum, which draws out the fuel. This vacuum is always changing depending on the engine conditions. Therefore, for this type the engine ECU calculates the fuel injection amount per injection duration in accordance with the changes in the intake manifold vacuum to ensure that the injector properly injects the fuel.
2. Type 2
This type is equipped with a delivery pipe that continually regulates the fuel pressure to keep the fuel pressure higher than a determined pressure from the manifold pressure. The basic operation is the same as type 1, but because the manifold vacuum is applied to the diaphragm’s upper chamber, the fuel pressure is controlled by changing the fuel pressure when the valve is opened in accordance with the manifold vacuum. The fuel is returned to the fuel tank via the fuel return pipe.
HINT:
The injection port of the injector is applied the vacuum by the manifold vacuum, which draws out the fuel. This vacuum is always changing depending on the engine conditions. Therefore, for this type the fuel pressure is continuously regulated in accordance with the intake manifold vacuum to keep the fuel pressure above a set pressure to maintain a set injection amount per injection duration.
Gasoline Engine Pulsation Damper
The pulsation damper uses a diaphragm to absorb a slight amount of fuel pressure pulsation generated by the fuel injection and the compression of the fuel pump.
SERVICE HINT:
The fuel pressure can be inspected easily by the screw of the pulsation damper.
HINT:
Some engine models do not have a pulsation damper.
Injector
The injector injects fuel into the intake ports of the cylinders in accordance with the signal from the engine ECU. The signals from the engine ECU cause current to flow in the solenoid coil, which causes the plunger to be pulled, opening the valve to inject the fuel. Because the plunger stroke does not change, the amount of the fuel injection is controlled at the time the current is flowed to the solenoid.
SERVICE HINT:
Handling of the O-ring:
The O-ring must not be reused.
When installing the O-ring, first coat it with new gasoline.
When installing the injector to the delivery pipe, be careful not to damage the O-ring.
With the injector installed in the delivery pipe, turn the indicator by hand. If it does not rotate smoothly, the Oring is damaged.