The Yanmar injector pump delivers precisely metered and timed bursts of fuel to the fuel injectors via the injector lines. Fuel is delivered to the injector pump by a low pressure feed pump (lift pump).
The injector pump draws fuel from the feed supply and distributes high pressure fuel to the injectors and the spill circuit. Air leaks and fuel restrictions reduce the amount of fuel that the lift pump delivers to the injector pump.
Worn components inside the injector pump reduce the pump output and lead to poor or non-running conditions. Poor adjustments of the governor and bad fuel timing can mimic injector pump problems and should be eliminated as possibilities before tackling the injector pump.