BOSCH Electronic Fuel Injection: Operation
- Fuel drawn from tank by fuel pump, passes through filter into main fuel supply. Pressure regulator, connected at end of main fuel supply, limits fuel pressure to 28 PSI. The electromagnetic injectors are connected to main fuel supply via fuel distribution pipes.
- Excess fuel from pressure regulator can flow through a second line back to fuel tank. A by-pass return line, coming from fuel pump, leads into this line. A pressure relief valve, in fuel pump, comes into operation when pressure rises considerably above normal (should pressure regulator develop a defect). A check valve in pressure line connection of fuel pump prevents pressure in main fuel supply from dropping immediately when pump is switched off.
- Fuel injectors are opened electrically in pairs by the electronic control unit and, due to pressure, fuel is injected. Injector jet is accurately calibrated and because fuel pressure is constant, amount of fuel injected depends only on length of time injector is kept open.
- Injection time is "computed" by electronic control unit. Information processed by electronics in control unit comes from individual sensors on engine. The moment when fuel is injected is controlled by distributor contacts 1 and 2 according to position of camshaft. These contacts are installed under the centrifugal advance device in distributor and are maintenance free.
- Injection time is governed by two factors, engine speed and load condition of engine. Engine speed is relayed to control unit by distributor contacts 1 and 2. Load condition is indicated by pressure in intake air distributor. Prevailing pressure here is converted to an electrical impulse and relayed to control unit by pressure sensor which is connected to intake air distributor by a hose.
- Electronic control unit processes this information and gives a signal for the injectors to be opened for a longer or shorter period of time. Control unit allows a varying amount of fuel to pass through the electrically operated injectors, depending on engine load and engine speed. This governs "basic amount" of fuel.NOTE: Electronic Control Unit cannot be repaired.
- In addition to basic amount of fuel, an accurately measured amount of fuel is additionally injected when starting at low outside temperatures, when engine is warming up and at full throttle.
- Enrichment of mixture for starting is dependent on engine temperature. Temperature is relayed from two temperature sensors to the control unit. The information is then sent to the cold start valve which provides extra fuel for approximately 8 seconds. As temperature rises, the injection time reduces, and at approximately 130-140°F the cold start valve stops giving extra fuel at starting. The cold start valve injects only when starter motor is operating to prevent engine flooding.
- This information is processed by the control unit in relation to basic fuel quantity, and impulses are relayed electrically to fuel injectors.
- During conditions of acceleration, throttle valve closes and engine speed is increased. Throttle valve switch cuts off fuel supply when throttle released for coasting or deceleration above preset RPM. If below a lower preset RPM, fuel supply is switched on again. This allows for smoother return to idle.
- Injectors of one pair of cylinders, inject fuel past the open intake valves, into combustion chamber during intake stroke, while injectors of other set of cylinders inject, onto the still closed intake valves, while exhaust gases are being forced out. In the latter case, fuel is "stored" at the intake valves.
- Amount of air is controlled during vehicle operation by a throttle valve in the intake air distributor. When idling, throttle valve is completely closed. Idling air can reach intake air distributor only via by-pass system in intake air distributor. Idling speed is adjusted by altering cross section of by-pass system. Adjustment must be carried out with engine at operating temperature.
- Engine, if it has not reached operating temperature, requires an additional amount of air. This is controlled by auxiliary air regulator. It alters functional cross section of auxiliary air line in accordance with temperature. Position of rotary valve is governed by a bi-metal spring which protrudes into crankcase.