Fuel System Function - Case CX Series Service Training Manual

CX210/CX240 ELECTRONIC FUEL SYSTEM

FUEL SYSTEM FUNCTION

Fuel is drawn from the fuel tank and passes through an inline filter prior to entering the fuel lift
pump. The 24 Volt DC pump is controlled by the Electronic Control Module through pulse width
modulation (PWM). The pump operates at a maximum pressure of 10 PSI when the engine is
running and at a maximum pressure of 7 PSI when cranking. Pressures greater than 7 PSI can
result in hard start/ no start problems. A relief valve in the head of the pump re-circulates the fuel
and regulates discharge pressure. The pump will run for 2 seconds when the key is turned on.
When cranking, the pump runs and continues to run for 25 seconds after cranking stops. The
pump runs continuously when the engine is running however, if the engine stops with the key still
on, the pump stops running. A 528 mesh screen at the inlet to the lift pump can be removed and
cleaned if required.
The fuel filter/ water separator is located between the fuel lift pump and the fuel injection pump.
Water will collect in the lower portion of the filter and must be drained to prevent damage to the
fuel injection pump. A water in the fuel (WIF) sensor alerts the operator when water should be
vented from the filter.
Fuel entering the Bosch VP44 Fuel Injection Pump fills the pump housing with fuel. Fuel is used
for cooling and lubricating the pump components. Fuel first enters a vane type transfer pump
which has a maximum regulated pressure of 300 PSI. Excess fuel from the vane pump regulator
returns to the vane pump inlet. Fuel from the vane pump enters a metering control valve through
a fill slot in the pump rotor.
When the Fuel Pump Control Module (FPCM) indicates no fuel needed, fuel flows through the
open metering valve and to the discharge valve in the distributor at transfer pump pressure. Fuel
at transfer pressure also forces the three pumping plungers outward against the cam ring. As the
pump shaft rotates, the pumping plungers are forced inward by the lobes on the cam ring, forcing
fuel to flow back through the open metering valve. At this time, as dictated by the FPCM, the
metering valve closes, forcing the fuel to flow out the discharge fitting and on to the specific fuel
injector. Although the injectors popping pressure is set at 4500 PSI, fuel pressure can reach
20,000 PSI during the injection period. When the proper amount of fuel has been delivered as
determined by the FPCM, the metering valve opens and allows fuel to flow back through the open
metering valve. With each revolution of the injection pump, fuel is supplied to all six cylinders in
the proper firing order. The ECM determines the quantity of fuel needed and sends this
information to the FPCM. The FPCM then determines the time of injection based on ECM
information of the engine's load and speed.
Fuel temperature in the injection pump is measured by an internal temperature sensor. The
temperature is monitored by the FPCM which adjusts fuel flow based on the temperature. Heat is
removed from the injection pump by providing an excess supply of fuel. A return flow line with an
overflow valve allows 70% of the fuel supplied to be returned to the tank. The overflow valve
uses a spring and check ball to regulate housing pressure at approximately 14 PSI. A small vent
prior to the check ball allows venting of air from the housing.
CX EXCAVATORS
8 - 9