Service Manual Manual

SECTION 3 - CHASSIS & TURNTABLE
3-128 – JLG Lift – 3120788
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 operat-
ing 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
- Crack s
- 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 man-
ifold leakage than the gasoline fuel supply system.
 Check for the following:
- Vac uum leaks
- Improper v alve timing
- Low compress ion
- Bent pushro ds
- Worn rocker arms
- Broken or we ak valve spri ngs
- Worn ca mshaft lo bes.
 Check the intake and exhaust manifolds for casting flash.
Table 3-12. Symptom Diagnosis
Checks Action