System Description

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

Fuel system is recirculating type. Fuel pump is now located inside fuel tank. Fuel system is recirculating type with fuel tank mounted across car behind rear seat. Fuel is drawn into an in-tank fuel module which houses fuel pump. A 70 micron filter is incorporated in inlet port of fuel module to prevent entry of dirt. A 400 micron rock filter is included in inlet port of fuel pump for further protection from dirt.

Fuel is pumped from base of fuel tank through flex hose to in-line filter under car and then to fuel rail.

Fuel rail is mounted on engine with a fuel pressure regulator fitted at return port of rail. Regulator is used to maintain constant fuel pressure of 35 - 45 lb sq in, for delivery to injectors.

Excess fuel is returned to fuel module through return lines and hoses. A 70 micron filter is fitted to return inlet. Both feed and return ports of fuel module have non-return valves fitted.