JLG 680S, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3121234 3-203
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 sensor 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 operating 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.
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 or Exhaust System in the GM Base Engine Service
Manual.
Table 3-13. Symptom Diagnosis
Checks Action