GASOLINE FUEL INJECTION SYSTEMS
OBJECTIVE: Identify and describe the different gasoline fuel injection systems.
gasoline injection system uses pressure from an electric fuel pump to spray fuel into the
engine intake manifold. Like a carburetor, it must provide the engine with the correct
air-fuel mixture for specific operating conditions. Unlike a carburetor, however,
PRESSURE, not engine vacuum, is used to feed fuel into the engine. This makes the gasoline
injection system very efficient.
injection system has several possible advantages over a carburetor type of fuel system.
Some advantages are as follows:
atomization. Fuel is forced into the intake manifold under pressure that helps break fuel
droplets into a fine mist.
fuel distribution. Equal flow of fuel vapors into each cylinder.
idle. Lean fuel mixture can be used without rough idle because of better fuel distribution
and low-speed atomization.
emissions. Lean efficient air-fuel mixture reduces exhaust pollution.
cold weather drivability. Injection provides better control of mixture enrichment than a
engine power. Precise metering of fuel to each cylinder and increased air flow can result
in more horsepower output.
parts. Simpler, late model, electronic fuel injection system have fewer parts than modern
There are many
types of gasoline injection systems. Before studying the most common ones, you should have
a basic knowledge of the different classifications. Systems are classified either single-
or multi-point injection and indirect or direct injection.
The point or
location of fuel injection is one way to classify a gasoline injection system. A
single-point injection system, also call throttle body injection (TBI), has the injector
nozzles in a throttle body assembly on top of the engine. Fuel is sprayed into the top
center of the intake manifold.
injection system, also called port injection, has an injector in the port (air-fuel
passage) going to each cylinder. Gasoline is sprayed into each intake port and toward each
intake valve. Thereby, the term multi-point (more than one location) fuel injection is
injection system sprays fuel into the engine intake manifold. Most gasoline injection
systems are of this type. Direct injection forces fuel into the engine combustion
chambers. Diesel injection systems are direct type.
three basic configurations of gasoline fuel injectiontimed, continuous, and throttle