4-2. FUEL INJECTORS MAINTENANCE
This task covers disassembly, cleaning, inspection, reassembly, and adjustment of
fuel injector nozzles. It also includes a short theory of operation.
THEORY OF OPERATION
Fuel injectors consist of the items shown below.
A measured quantity of fuel under high pressure moves from fuel injection pump
through inlet to high pressure channel in injector body. Fuel then moves through
valve stop channel and enters pressure chamber which surrounds valve in injector
When pressure of fuel against valve is more than control spring force, valve is
moved from its seat at sac in injector tip. This permits fuel under high pressure to
enter sac. Fuel then moves from sac through spray orifices to combustion chamber;
fuel reaches combustion chamber in atomized condition.
When fuel delivery stops, pressure against valve is decreased and control spring im-
mediately returns valve to its seat; this removes danger of leakage after measured
amount of fuel has been released. Valve opens and closes rapidly with clear noise.
During injection, a small amount of fuel leaks through controlled clearance between
injector tip and injector body; this leakage adds lubrication to all moving parts in
fuel injector. This fuel then moves through leak off channel, leak off fitting, leak
off lines and returns to fuel tank.