CX210/CX240 ELECTRONIC FUEL SYSTEM
8 - 10
CX EXCAVATORS
FUEL SYSTEM FUNCTION
Fuel from the injection pump is sent to the injectors through high pressure injection lines in
accordance with the engines firing order. The high pressure lines are connected to the
distributor housing fittings at the pump and at fuel connectors at the cylinder head. The
connectors direct the fuel through edge filters and on to the injectors. Fuel pressure builds in
the injector until pressure under the needle becomes greater than the injector spring pressure
allowing the needle to raise. Small spray holes in the injector tip allows fuel to exit the
injector. Leakage from the injector passes through a rifled passage drilled through the length
of the cylinder head and joins the return flow of fuel.
Pump timing is altered by changing the position of the cam ring in the injection pump. Timing
is controlled by the master piston in the timing advance mechanism. During the cranking
cycle the return spring holds the master piston and cam ring in the retarded position. This
causes injection to occur at approximately top dead center. Transfer pressure is delivered to
the master piston control valve and servo. As engine speed increases, transfer pressure
increases causing the master piston to move, compressing the return spring, causing the
cam ring to rotate and causing injection to occur earlier.
The pulsing timing control valve, activated by the ECM, can retard timing when energized, by
venting pressure from the advance mechanism and allowing the return spring to move the
master piston in the retard direction. This feature permits changes in timing up to 30 engine
degrees.
The calculated timing of the Engine ECM is sent to the FPCM where it is controlled. An
Incremental Angle Timing (IAT) ring in the injection pump determines the beginning and end
of injection. Timing information from the IAT is compared to the timing information from the
ECM for accuracy. If a variation of 3 degrees or more occurs, the FPCM data is retained
however, the engine will operate at a reduced output (limp home mode).
The Bosch VP44 injection pump is fixed position mounted and cannot be rotated to alter
timing. Static pump timing for a specific application is obtained through the use of the proper
drive shaft key. Keys are offset as required by the timing requirements, based on pump
manufacturers tolerances. Keys are identified by a two digit part number on the top of the
key along with an arrow which points toward the injection pump. The required key part
number can be found on the injection pump identification plate.
To Next Page
Loading...
