Haltech E6A - Manual (Page 88)

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Running two fuels pumps continuously, or else a single very large flow-rate pump (if one is
available) means excessive noise and heating of the fuel. A street vehicle with very high
potential output will not need a large fuel supply at all times. The second pump would only be
activated when load demands require that the extra flow be available.
NB: The extra fuel pump cannot be driven directly by the ECU. The ECU can be made to
drive a relay to power the pump.
To use the Auxiliary Fuel Pump function, you must have the following:
- a properly plumbed fuel pump, wired through a relay;
- E6A programming software and cable.
The extra pump must be connected in parallel with the primary fuel pump. Figure 16.6
suggests a possible layout. The check valve is necessary to prevent fuel from being forced in
the wrong direction. Connect the power to the pump via a relay as shown. Either the positive
or negative side may be switched through the relay.
Run the E6A programming software Online and select the Auxiliary Fuel Pump function on the
appropriate output. There are two parameters that define when the Auxiliary Pump will be
switched on.
Load Bar: This is the bar number on the fuel maps which must be exceeded for the extra fuel
pump to be switched on. If you wish to switch the extra fuel pump only by engine speed, set
this to 32.
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.