Tracker Valve - Mercury Optimax 250 Manual

DIRECT FUEL INJECTION

Tracker Valve

The tracker valve is located on the starboard fuel/air rail assembly.
The DFI system must maintain a constant 10 psi pressure difference between the fuel
pressure and air pressure in the rails, at all times. The tracker is designed to maintain the
10 psi differential when the air or fuel pressure suddenly raises (i.e. pulses generated by
the compressor's piston or by the fuel injectors opening and closing). The tracker contains
a spring on the air side of the diaphragm. This spring positions the diaphragm against the
diaphragm's seat (when the engine is not running).
After the engine starts, and the fuel and air pressure reach normal operating range, the
fuel pressure will compress the spring and the diaphragm will move slightly away from the
seat (to a neutral position). At this point the pressure on both sides of the tracker dia-
phragm is equal (10 psi spring pressure + 80 psi air pressure = 90 psi fuel pressure).
Any air or fuel pressure "spikes" on one side of the diaphragm will transfer this pressure
rise to the other system (air or fuel) on the other side of the diaphragm. Both systems will
have a momentary increase in pressure so that the 10 psi difference between air and fuel
system pressures can be maintained.
NOTE: To prevent excessive wear in the seat, the tracker is calibrated to allow the dia-
phragm to be slightly away from the seat during normal operation.
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90-888438 JUNE 2002