JLG 400S Service And Maintenance Manual page 208

SECTION 3 - CHASSIS & TURNTABLE
Checks
Exhaust System Checks
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
Sensor Checks
Fuel System Checks
Ignition System Checks
Engine Mechanical Checks
Exhaust System Checks
3-150
Table 3-14. GM Engine Symptom Diagnosis
² 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.
² Check for possible plugged catalytic converter. Refer to Restricted Exhaust System Diagnosis
² Refer to Important Preliminary Checks.
² Make sure the vehicle's operator is using the correct starting procedure.
²Check 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
² Check the Crankshaft Position (CKP) sensor.
²Check the Throttle position (TPS) sensor.
Important: A closed LPG manual fuel shut off valve will create an extended crank OR no start condition.
² Verify the excess flow valve in the LPG manual shut-off valve is not tripped.
² Check mixer module assembly for proper installation and leakage.
² Verify proper operation of the low pressure lock-off solenoids.
² Verify proper operation of the EPR
² Check for air intake system leakage between the mixer and the throttle body.
² Check the fuel system pressures. Refer to the Fuel System Diagnosis.
Note: LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating conditions.
² Check for the proper ignition voltage output with J 26792 or the equivalent.
² Verify that the spark plugs are correct for use with LPG (R42LTS)
² Check the spark plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
² Check for bare or shorted ignition wires.
² Check for moisture in the distributor cap if applicable.
² 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.
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.
² Check for the following:
- Vacuum leaks
- Improper valve timing
- Low compression
- Bent pushrods
- Worn rocker arms
- Broken or weak valve springs
- Worn camshaft lobes.
² Check the intake and exhaust manifolds for casting flash.
² 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.
² Check for possible plugged catalytic converter. Refer to Restricted Exhaust System Diagnosis or Exhaust System in the GM Base Engine Service
Manual
Action
Hard Start
3121671