Fuel Injector: Description and Operation

Fuel Injector:

WARNING: When checking the fuel injectors, never apply battery voltage directly to the solenoid, injector coil damage may occur.

PURPOSE

The fuel injectors are electro-mechanical devices which deliver, meter and atomize fuel to the engine.

OPERATION

The fuel injectors are mounted in the lower intake manifolds and positioned so that their tips are directing fuel at the back face of the intake valve. The body is a solenoid-actuated valve assembly. Therefore, fuel flow to the engine is regulated only by how long the solenoid is energized. Atomization of the fuel is obtained by a director/metering plate where the fuel leaves the fuel injector.
An electrical signal from the powertrain control module activates the solenoid windings of the Injector, causing the needle valve to move inward off the seat. This allows the pressurized fuel from the fuel pump to flow through the orifice and to spray into the intake manifold runners above the intake valve.

CONSTRUCTION

For maximum efficiency and for calibration accuracy, the fuel injector must have very little mechanical working lag of the needle valve for quick response. For this purpose the injection coil has very few windings and low inductance. Such a coil can, however, be burned out due to excessive current flow when energized.
At idle speed and up to 4,500 rpm, fuel is supplied by simultaneously providing one injection per crankshaft rotation (two injections per cycle) to all cylinders. Therefore, one injection period supplies half of the fuel necessary for ideal combustion.
Between 4,500 and 6,000 rpm, the fuel injectors could remain fully open due to fuel injector lag, resulting in poor performance and fuel control. For this reason, when the engine speed exceeds 4,500 rpm, there is a changeover to one injection per two crankshaft rotations (one injection per cycle). The fuel injectors stay open longer and the time the fuel injectors remain closed is reduced. The amount of fuel necessary for ideal combustion is supplied by one injection.
When engine speed reaches 6,300 rpm or higher, fuel injection is shut off in order to prevent engine over-speed, and possible engine damage.