JLG 4394RT Service Manual - Manual (Page 67)

SECTION 3 - CHASSIS & SCISSOR ARMS
3121133 – JLG Sizzor – 3-31
3.6 FORD EFI ENGINE
Performing Diagnostics
1. Verify the complaint and determine if it is a deviation
from normal operation.
2. Once the complaint has been verified, preliminary
checks can be done. Conduct a thorough visual
inspection, be alert for unusual sounds or odors,
and gather diagnostic trouble code information.
3. Perform a system check that will verify the proper
operation of the system in question and check for
recent information updates.
4. If a diagnostic trouble code (DTC) is stored, contact
a JLG distributor to make an effective repair.
5. If no DTC is stored, select the symptom from the
symptom tables and follow the diagnostic path or
suggestions to complete the repair.
6. After the repair has been made and validated for
proper operation, the old part should be momen-
tarily re-installed to verify that it was indeed the
source of the problem.
If no matching symptom is available, analyze the com-
plaint and develop a plan for diagnostics utilizing the wir-
ing diagrams, technical assistance, and repair history.
Intermittent conditions may be resolved by using a check
sheet to pinpoint the circuit or electrical system compo-
nent. Some diagnostic charts contain Diagnostic Aids
which give additional information about a system. Be sure
to use all of the information that is available to
you.
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.
EFI Diagnostics
The EFI diagnostics are designed to assist in locating a
faulty circuit or component. When a malfunction is
detected by the Engine Control Module (ECM), a diagnos-
tic trouble code (DTC) is set and will be displayed on the
JLG Control System Analyzer. Refer to Section 6 - JLG
Control System.
CLEARING TROUBLE CODES
To clear the trouble codes from the ECM, the electrical
current running to the ECM must be shut off. To do this,
disconnect the negative terminal from the battery for a
period of approximately 15 minutes.
ECM 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.