TM 10-3950-672-24-2
During the injection cycle, high pressure from the
injection pump rises to the operating (pop) pressure
which causes the needle valve in the injector to lift.
Fuel is then injected into the cylinder. A shimmed
spring is used to force the needle valve closed as the
injection pressure drops below the pop pressure to seal
off the nozzle after injection.
Failure of the needle valve to lift and close at the correct
time or needle valve stuck open can cause the engine to
misfire and produce low power. Fuel leaking from the
open nozzle can cause a fuel knock, poor performance,
smoke, poor fuel economy, and rough running.
Caution: Be sure to tighten the fuel line nut before
proceeding to the next injector.
To find which cylinder is misfiring, operate the engine
and loosen the fuel line nut at one injector and listen for
a change in engine speed.
Note: A drop in engine speed indicates the injector
was delivering fuel to the cylinder.
Check each cylinder until the malfunctioning injector is
found.
Remove the malfunctioning injector to test or replace it.
If the engine continues to misfire after replacing the
injector, check for leaks in the high pressure line. Also
check for a defective delivery valve that lets the fuel
drain back into the injection pump.
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