Haltech F9A - Manual (Page 95)

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Engine Speed: The extra fuel pump will turn on when the engine speed exceeds this
parameter. If you wish to switch the pump only by load, set this parameter high.
Run Time: The auxiliary fuel pump will switch on if the engine exceeds the engine speed
and/or the load bar set above. It will then stay on, even after speed and load have dropped
below their respective limits, for a period of time specified by Run Time. A minimum Run
Time of 5 seconds is permitted.
The Auxiliary Fuel Pump will prime with the main fuel pump, but will only run if the engine
condition exceeds either limit. Since there may be a short delay from the time the fuel pump is
switched on to the time the extra fuel becomes available, the Load Bar and Engine Speed
settings above should be set below when that extra fuel is actually needed. The use of a good
quality check valve and fuel pump will reduce the delay time by maintaining pressure in the
secondary line. Nevertheless, the extra fuel will not be instantly available and care should
taken when deciding the switch times. If these values are set too high, the engine may be
momentarily starved of fuel when there is a sudden fuel demand.