Toro Workman HDX Service Manual page 44

Fuel Injector
The fuel injector is an electromagnetic device that oper-
ates when voltage is delivered from the ECU for a prede-
termined amount of time. When energized, the injector
opens and allows fuel to travel through the injector. The
open injector allows a fine mist of highly atomized fuel
to be sprayed at the back of the intake valve through the
intake port. The longer the voltage is applied, the longer
the injector will stay open. The length of time the injector
is open is called the duty cycle. This duty cycle will go up
as engine RPM and load against the engine increase,
which causes more demand for fuel.
For the fuel injectors to deliver the precise amount of fuel
demanded by the ECU, the fuel pressure needs to be set
at exactly the recommended pressure rating by the
OEM. This should not deviate more than 1 to 2 PSI dur-
ing operation. Proper fuel pressure will also facilitate
quick starting because of proper fuel atomization.
Crankshaft Position Sensor
The crankshaft position sensor's function is to report
back to the ECU with the signals needed to calculate
RPM. It is also used to determine which stroke each cyl-
inder is on for proper timing of fuel injection and ignition
events. This sensor is required for the system to inject
fuel as the intake valve opens for most efficient perfor-
mance and idle quality. The signals are used to control
when to apply the ignition voltage to the spark plug for
the proper ignition--timing advance.
The crankshaft position sensor works by having a mag-
netic core tightly wrapped with wire. When a ferrous
metal passes near the sensor, the metal interrupts the
magnetic field and induces a voltage spike in the wire
coiled around the magnet. The voltage spike is seen by
the ECU as a sine wave and the ECU counts the number
of pulses it sees over a period of time. The ECU divides
the pulses by the number of cylinders the engine has to
determine the engine RPM.
Crankshaft Reluctor Wheel
The reluctor wheel is attached to the back of the crank-
shaft accessory drive pulley. This wheel works in con-
junction with the crankshaft position sensor to provide
the momentary interruption in the magnetic field needed
to produce a voltage spike for the ECU to determine en-
gine RPM.
The largest gap in the Reluctor Wheel is used to tell the
ECU that the engine number 1 cylinder is at top dead
center. The ECU can now begin its sequence and follow
through the engine's firing order until the last injector has
been opened.
Briggs/Daihatsu Gasoline Engine Page 3 - - 26 Rev. A
Figure 26
Figure 27
Figure 28
Workman HDX