| 1: Fuel Pump | 6: Coolant Temp Switch |
| 2: Fuel Filter | 7: Auxilary air valve |
| 3: Fuel Pressure Regulator | 8: Throttle Position Switch (TPS) |
| 4: Injector | 9: Oxygen Sensor |
| 5: Air Flow Sensor | 10. ECU |
(1) Fuel Pump:
The electric Fuel Pump and filter are located at the rear of the car, external to the fuel tank. The pump operates for a few seconds whenever the ignition is switched on. This allows fuel pressure to build up before the engine is cranked. It operates continuously when the motor is cranking or running. The fuel pump supplies fuel several times more than the required pressure to the Fuel Pressure Regulator fitted in the fuel rail.
Read fuel filter section.
(3) Fuel Pressure Regulator:
The Fuel Pressure Regulator, maintains the injector supply pressure in the fuel rail at 2.5 Bar (approx 37psi) and in this system not adjustable. It maintains the pressure in the fuel rail by restricting the amount of fuel returned to the tank. Manifold vacuum is applied to the regulator and when the vacuum drops in the intake manifold as in acceleration, the fuel pressure will raise approx .5 Bar.
(4) Injector:
The entry point of fuel into the intake manifold. There is one injector per cylinder and they are electro-magnetically activated. The time they are activated is measured in m/s (milliseconds). The injector is designed to spray fuel into the manifold in an atomized state so that the fuel mixes effectively with the incoming air. The injection valves squirt twice every camshaft revolution and when the inlet valves open the fuel is entrained by the flow of intake air.
(5) Air Flow Sensor:
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This is the main control variable in determining the quantity of fuel injected. The Air flow sensor has a flap inside the sensor. As air is drawn through the sensor the flap rotates and a set of contacts move along a variable resistance track. This sends a variable voltage to the ECU in proportion to the air drawn into the engine. This sensor is more commonly known as a potentiometer. |
The coolant sensor when cold, tells the ECU to richen the mixture. As the engine warms up, the resistance through the sensor changes and therefore this tells the ECU to progressively return injection duration to normal as it reaches operating temperature.
(7) Auxilary Air Valve:
A cold motor needs to idle slightly faster requiring a little additional air and fuel. This system uses an Auxiliary Air Valve, which allows a small amount of air to bypass the throttle butterfly when cold, gradually reducing the amount as the element in the valve warms up. This is the same as holding the throttle slightly open. The ECU automatically supplies the matching fuel as dictated by the air flow meter and temp sensor.
(8) Throttle Position Switch: (TPS)
(9) Oxygen Sensor:
Some early L systems did not use an oxygen sensor. In Australia they were introduced on the LE system. See my other article on O2 sensors and testing.
(10)ECU:
The ECU determines how much fuel is needed and controls how long the injectors are held open during each piston stroke. The ECU will vary this duration in accordance with inputs from the following sensors:
- The main input is the intake Manifold Pressure Sensor (MPS) which measures airflow by monitoring the intake manifold pressure (for the oldies - vacuum) It is connected to the intake manifold via a rubber hose.
- Throttle position and relative movement of the throttle from the Throttle Position Switch (TPS), which is connected to the butterfly shaft.
- Coolant temperature from a Temperature Sensor, which is generally fitted in the cylinder head near the thermostat housing.
- Ambient air temperature from an air temperature sensor, which is generally located in the air cleaner box and,
- a set of dual trigger points, located in the base of the distributor which synchronize the timing of the fuel injectors to the correct piston strokes.