Fuel Delivery and Air Induction: Description and Operation

Influence Of Air/Fuel Ratio On Power, Economy And Emissions:

PRINCIPAL TASK

The principal task of the fuel injection system is to deliver the correct amount of fuel to each cylinder under various engine speeds and load conditions.

The theoretically ideal air/fuel mixture (stoichiometric ratio) is 14.7 : 1. This means the chemical minimum for complete combustion is 14.7 kg of air to every 1 kg of fuel.

Most contemporary engines operate at maximum fuel economy and least emissions output with a mixture of 15.0 : 1.

Because the vehicle engine usually operates in the partial load condition, it is designed for maximum fuel economy in that range. For the other conditions, such as cold start, idle and full load, the fuel mixture is enriched.

FUEL METERING

Fuel is delivered to solenoid operated injectors, through a fuel pressure regulator, by an electric fuel pump operating at constant pressure. Injector pressure will fluctuate between 35 - 45 lb sq in, depending on engine manifold pressure acting on fuel pressure regulator. The amount of fuel injected for a given duration of injector open time is maintained constant, regardless of back pressure on injector nozzles. Accurate fuel monitoring is achieved in this way.

Injectors are operated by an electrical pulse that actuates a solenoid valve inside injector body. The pulse duration, calculated by the ECU, determines quantity of fuel injected. ECU receives information from sensors regarding intake air volume, engine speed, and coolant temperature. This information is used to access mapped data stored in 128 memory locations containing injector pulse durations pertaining to eight engine loads at sixteen different speeds.

Fuel System:

FUEL SUPPLY SYSTEM

Fuel system is recirculating type. Fuel tank is mounted across car behind rear seat. An electric pump draws fuel from fuel tank. Fuel is delivered through a fuel filter to fuel rail on engine. A pressure regulator is fitted to fuel rail to maintain constant fuel pressure at 35 - 45 lb/sq in across injectors. The fuel pump supplies a larger amount of fuel then is ever needed by the system. The excess fuel is returned to the gas tank via the left hand pressure regulator, fuel cooler and return line. This constant flushing with cool fuel enables the overall system temperature to drop. This helps to avoid the formation of vapor bubbles and enables good hot starting characteristics. Fuel pump is energized only when ECU senses engine cranking signal or engine running signal.

The components addressed for the fuel system are:
^ Air Cleaner Assembly
^ Air filter Element
^ EVAP system
^ Fuel Cooler
^ Fuel filter
^ Fuel injectors
^ Fuel pressure regulator
^ Fuel pump
^ Fuel pump relay
^ Fuel rail
^ Fuel return line
^ Fuel supply line
^ Fuel tank
^ Inertia Switch
^ Intake air hoses
^ Overrun Valve
^ Power Resistor
^ Throttle Butterfly Valve
^ Throttle body
^ Throttle cable
^ Throttle Linkage
^ Throttle Pedal