JLG 740AJ Service Manual - Manual (Page 143)

SECTION 3 - CHASSIS & TURNTABLE
3121160 – JLG Lift – 3-91
Engine Module and Sensors
CRANKSHAFT POSITION (CKP) SENSOR
The crankshaft position (CKP) sensor provides a signal
used by the Engine Module to calculate the ignition
sequence. The CKP sensor initiates the reference pulses
which the Engine Module uses to calculate RPM and
crankshaft position.
CAMSHAFT POSITION (CMP) SENSOR AND
SIGNAL
The camshaft position (CMP) sensor sends a CMP signal
to the Engine Module. The Engine Module uses this signal
as a "sync pulse" to trigger the injectors in the proper
sequence. The Engine Module uses the CMP signal to
indicate the position of the #1 piston during its power
stroke. The CMP uses a Hall Effect sensor to measure pis-
ton position. This allows the Engine Module to calculate
true sequential fuel injection (SFI) mode of operation. If
the Engine Module detects an incorrect CMP signal while
the engine is running, DTC 53 will set. If the CMP signal is
lost while the engine is running, the fuel injection system
will shift to a calculated sequential fuel injection mode
based on the last fuel injection pulse, and the engine will
continue to nun. As long as the fault is present, the engine
can be restarted. It will run in the previously established
injection sequence.
ENGINE COOLANT TEMPERATURE (ECT)
SENSOR
The engine coolant temperature (ECT) sensor is a g
thermistor (a resistor which changes value based on tem-
perature) mounted in the engine coolant stream. Low
coolant temperature produces a high resistance of
100,000 ohms at -40°C (-40°F). High temperature causes
a low resistance of 70 ohms at 130°C (266°F). The Engine
Module supplies a 5-volt signal to the ECT sensor through
resistors in the Engine Module and measures the voltage.
The signal voltage will be high when the engine is cold
and low when the engine is hot. By measuring the voltage,
the Engine Module calculates the engine coolant temper-
ature. Engine coolant temperature affects most of the sys-
tems that the Engine Module controls.
After engine start-up, the temperature should rise steadily
to about 85°C (185°F). it then stabilizes when the thermo-
stat opens. If the engine has not been run for several
hours (overnight), the engine coolant temperature and
intake air temperature displays should be close to each
other. A fault in the engine coolant sensor circuit will set
DTC 33 or DTC 43.