JLG 4394RT Service Manual - Manual (Page 159)

SECTION 3 - CHASSIS, PLATFORM & SCISSOR ARMS
3121249 – JLG Lift – 3-123
Exhaust System Checks • Check the exhaust system for a possible restriction:
- Inspect the exhaust system for damaged or collapsed pipes
- Inspect the muffler for signs of heat distress or for possible internal failure
• Check for possible plugged catalytic converter. Refer to Restricted Exhaust System Diagnosis.
Hard Start
DEFINITION: The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but immediately dies.
Preliminary Checks
• Refer to Important Preliminary Checks.
• Make sure the vehicle's operator is using the correct starting procedure.
Sensor Checks • Check the Engine Coolant Temperature sensor with the scan tool. Compare the engine coolant temperature
with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees
greater or less than the ambient air temperature on a cold engine, check for high resistance in the coolant sen-
sor circuit. Refer to DTC 111.
• Check the Crankshaft Position (CKP) sensor.
• Check the Throttle position (TPS) sensor.
Fuel System Checks Important: A closed LPG manual fuel shut off valve will create an extended crank OR no start condition.
• Verify the excess flow valve in the LPG manual shut-off valve is not tripped.
• Check mixer module assembly for proper installation and leakage.
• Verify proper operation of the low pressure lock-off solenoids.
• Verify proper operation of the EPR.
• Check for air intake system leakage between the mixer and the throttle body.
• Check the fuel system pressures. Refer to the Fuel System Diagnosis.
Ignition System Checks Note: LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline oper-
ating conditions.
• Check for the proper ignition voltage output with J 26792 or the equivalent.
• Verify that the spark plugs are correct for use with LPG (R42LTS).
• Check the spark plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
• Check for bare or shorted ignition wires.
• Check for moisture in the distributor cap, if applicable.
• Check for loose ignition coil connections.
Important:
1. If the engine starts but then immediately stalls, Check the Crankshaft Position (CKP).
2. Check for improper gap, debris or faulty connections.
Engine Mechanical Checks Important: The LPG Fuel system works on a fumigation principle of fuel introduction and is more sensitive to intake
manifold leakage than the gasoline fuel supply system.
• Check for the following:
- Vacuum leaks
- Improper valve timing
- Low compression
- Bent pushrods
- Worn rocker arms
- Broken or weak valve springs
- Worn camshaft lobes
• Check the intake and exhaust manifolds for casting flash.
Table 3-16. Symptom Diagnosis
Checks Action