JLG 450A_AJ Series II Service Manual - Manual (Page 138)

SECTION 3 - CHASSIS & TURNTABLE
3-98 – JLG Lift – 3121290
Engine Mechanical Checks Important: The LPG Fuel system works on a fumigation principle of fuel introduction and is more sensi-
tive to intake manifold leakage than a 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.
Exhaust System Checks 1. Check exhaust system for a possible restriction:
- Inspect exhaust system for damaged or collapsed pipes
- Inspect muffler for signs of heat distress or internal failure.
2. Check for plugged catalytic converter. Refer to Restricted Exhaust System Diagnosis
Hard Start
DEFINITION: Engine cranks OK, but does not start for a long time. Engine does eventually run or may start, but immediately dies.
Preliminary Checks 1. Refer to Important Preliminary Checks.
2. Make sure operator is using correct starting procedure.
Sensor Checks 1. Check Engine Coolant Temperature (ECT) sensor with scan tool. Compare engine coolant temperature
with ambient air temperature on a cold engine. IF coolant temperature reading is more than 5 degrees
greater or less than ambient air temperature on a cold engine, check for high resistance in coolant sensor
circuit. Refer to DTC 111
2. Check Crankshaft Position (CKP) sensor.
3. Check the Throttle Position Sensor (TPS).
Fuel System Checks Important: A closed LPG manual fuel shut off valve will create an extended crank OR no start condition.
1. Verify excess flow valve in LPG manual shut-off valve is not tripped.
2. Check mixer module assembly for proper installation and leakage.
3. Verify proper operation of low pressure lock-off solenoids.
4. Verify proper EPR operation.
5. Check for air intake system leakage between mixer and throttle body.
6. Check the fuel system pressures. Refer to Fuel System Diagnosis.
Ignition System Checks Note: LPG being a gaseous fuel requires higher secondary ignition system voltages for equivalent gaso-
line operating conditions.
1. Check proper ignition voltage output with J 26792 or the equivalent.
2. Verify spark plugs are correct for use with LPG (R42LTS)
3. Check spark plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
4. Check for bare or shorted ignition wires.
5. Check for moisture in distributor cap if applicable.
6. Check for loose ignition coil connections.
NOTICE:
1. If engine starts but then immediately stalls, Check Crankshaft Position (CKP).
2. Check for improper gap, debris, or faulty connections.
Table 3-13. Symptom Diagnosis
Checks Action