JLG 660SJ Service Manual - Manual (Page 110)

SECTION 3 - CHASSIS & TURNTABLE
3-60 – JLG Lift – 3121202
VISUAL/PHYSICAL ENGINE INSPECTION
CHECK
Perform a careful visual and physical engine inspection
before performing any diagnostic procedure. Perform all
necessary repairs before proceeding with additional diag-
nosis, this can often lead to repairing a problem without
performing unnecessary steps. Use the following guide-
lines when performing a visual/physical inspection check:
• Inspect engine for modifications or aftermarket equip-
ment that can contribute to the symptom; verify that all
electrical and mechanical loads or accessory equip-
ment is "OFF" or disconnected before performing diag-
nosis.
• Inspect engine fluids for correct levels and evidence of
leaks.
• Inspect vacuum hoses for damage, leaks, cracks,
kinks and improper routing, inspect intake manifold
sealing surface for a possible vacuum leak.
• Inspect PCV valve for proper installation and operation.
• Inspect all wires and harnesses for proper connections
and routing; bent or broken connector pins; burned,
chafed, or pinched wires; and corrosion. Verify that
harness grounds are clean and tight.
• Inspect engine control module (ECM), sensors, and
actuators for physical damage.
• Inspect ECM grounds for cleanliness, tightness, and
proper location.
• Inspect fuel system for adequate fuel level, and fuel
quality (concerns such as proper octane, contamina-
tion, winter/summer blend).
• Inspect intake air system and air filter for restrictions.
• Inspect battery condition and starter current draw.
If no evidence of a problem is found after visual/physical
engine check has been performed, proceed to MIL DTC
retrieval procedure.
ECM/EPM and Sensors
CRANKSHAFT POSITION (CKP) SENSOR
The crankshaft position (CKP) sensor provides a signal
used by the engine control module (ECM) to calculate the
ignition sequence. The CKP sensor initiates the reference
pulses which the ECM uses to calculate RPM and crank-
shaft position.
CAMSHAFT POSITION (CMP) SENSOR AND
SIGNAL
The camshaft position (CMP) sensor sends a CMP signal
to the ECM. The ECM uses this signal as a "sync pulse" to
trigger the injectors in the proper sequence. The ECM
uses the CMP signal to indicate the position of the #1 pis-
ton during its power stroke. The CMP uses a Hall Effect
sensor to measure piston position. This allows the ECM to
calculate true sequential fuel injection (SFI) mode of oper-
ation. If the ECM 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.