Fuel Delivery and Air Induction: Description and Operation

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 injection. Additional sensors are used to monitor engine temperature, inlet air temperature and throttle position, etc, thereby ensuring 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.

Fuel Delivery / Canister Purge:

Fuel Pump Control:

Fuel Pumps:

FUEL DELIVERY

The 6.0 liter engine now uses two fuel pump modules to meet fuel requirements. Modules are identical but operate independently in two stages. One pump (A) operates continuously while engine is running. The second pump (B) is activated when engine speed exceeds 2840 rpm. Each pump is operated by a separate relay. Pump relay 1 is switched by EFI ECM; relay 2 by fuel pump control module. Fuel pump control module receives an engine speed input from Ignition ECM and switches relay 2 coil to ground when engine speed reaches 2840 rpm. When engine speed drops below 2000 rpm, ground is interrupted.

The fuel pumps 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

This system is controlled by EFI ECM. Power is derived from air injection relay. When air injection is enabled, (after all engine starts), current is applied to hot start switch. When fuel rail temperature is 158° F (70° C) or higher, switch closes and activates solenoid vacuum valve. This directs vacuum through delay valve to fuel pressure regulator. This momentary delay in vacuum increases fuel pressure to purge fuel rail.