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.

"P" System EFI:

"P" SYSTEM FUEL INJECTION - 12 CYLINDER

The "P" type electronic fuel injection system is an indirect injection system which incorporates solenoid operated low pressure injectors intermittently spraying fuel into the inlet port of each cylinder. A digital engine control module (ECM) with an integral manifold pressure sensor, governs the amount of fuel injected by controlling the duration of injection. The manifold pressure and speed signal, derived from ignition pulses, provide the main control for the fuel injected. Additional sensors are used to monitor engine temperature, inlet air temperature and throttle position, etc, thereby ensureing optimum fueling for all engine operating conditions.

Fuel metering is obtained by controling the length of time the injectors are held open during each engine cycle. The pulse duration is varied by the ECM according to inputs from the engine and chassis mounted sensors. For more information, refer to COMPUTERS AND CONTROL SYSTEMS.

Evaporative Emission Control And Fuel Delivery:

FUEL DELIVERY

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 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.

Hot Start System:

Hot Start System:

HOT START

Hot start system assists in engine starting during high underhood temperatures by increasing fuel pressure and purging fuel rail.

System consists of a 45 second timer, fuel rail temperature sensitive switch, and a normally open solenoid vacuum valve located in fuel pressure regulator vacuum line. Vacuum is applied to regulator through solenoid vacuum valve, during normal operation.

Each time ignition is switched ON, 45 second timer is activated and applies voltage to hot start switch. When fuel temperature is 158° (70° C) or higher, switch closes and allows voltage flow to close solenoid vacuum valve. Fuel pressure regulator vacuum is delayed causing an increase in fuel pressure to purge fuel rail.