Fuel Delivery and Air Induction: Description and Operation

Multiport Fuel Injection (MFI)

WARNING: Do not smoke or carry lighted tobacco or open flame of any type when working on or near any fuel-related component. Highly flammable mixtures are always present and may be ignited, resulting in possible personal injury.

DESCRIPTION
The Multiport Fuel Injection System (MFI) is classified as a multi-point, pulse time, speed density control, fuel injection system. Fuel is metered into each intake port in a sequential firing order. Fuel injectors pulse to follow engine firing order in accordance with engine demand through fuel injectors mounted on a tuned intake manifold assembly.

OPERATION
The Powertrain Control Module (PCM) accepts input from various engine sensors to compute the required fuel flow rate necessary to maintain a prescribed air/fuel ratio throughout the entire engine operational range. The PCM then outputs a command to the fuel injectors to meter the appropriate quantity of fuel.

The PCM also determines and compensates for the age of the vehicle and its uniqueness. The PCM will automatically sense and compensate for changes in altitude (i.e., from sea level to mountains) and will also permit push-starting the vehicle should it become necessary (manual transmission only).

Fuel Injection Timing
Each fuel injector is energized once every other crankshaft revolution in sequence with engine firing order. The period of time that the fuel injectors are energized (fuel injector "on time" or pulse width) is controlled by the vehicle's PCM. Air entering the engine is monitored by flow, pressure and temperature sensors. The outputs of these electronic engine control sensors are processed by PCM. The PCM determines the needed fuel injector pulse width and outputs a command to the fuel injector to meter the exact quantity of fuel.