JLG 450A_AJ Series II Service Manual - Manual (Page 143)

SECTION 3 - CHASSIS & TURNTABLE
3121290 – JLG Lift – 3-103
Engine Mechanical Check Check engine for the following:
- Broken motor mounts.
- Improper valve timing.
- Low compression.
- Bent pushrods.
- Worn rocker arms.
- Broken or weak valve springs.
- Worn camshaft lobes.
Surges/Chuggles
DEFINITION: Engine has a power variation under a steady throttle or cruise. Vehicle feels as if it speeds up and slows down with no change
in accelerator pedal.
Preliminary Checks Refer to Important Preliminary Checks.
Sensor Checks Check Heated Exhaust Gas Oxygen Sensor (HEGO) performance.
Fuel System Checks 1. Check Rich or Lean symptom that causes condition. Drive vehicle at speed of complaint. Monitoring
oxygen sensors will help identify problem.
2. Check fuel pressure while condition exists. Refer to LPG Fuel System Diagnosis.
3. Verify proper fuel control solenoid operation.
4. Verify LPG manual shut-off valve is fully open.
5. Check in-line fuel filter for restrictions.
Ignition System Checks 1. Check proper ignition output voltage using spark tester J26792 or equivalent.
2. Verify spark plugs are correct for use with LPG (R42LTS).
3. Check spark plugs. Remove and inspect plugs for the following conditions:
- Wet plugs.
- Cracks.
- Wear.
- Improper gap.
- Burned electrodes.
- Heavy deposits.
4. Check Crankshaft Position (CKP) sensor.
Additional Check 1. Check ECM grounds clean, tight, and in proper locations.
2. Check generator output voltage.
3. Check vacuum hoses for kinks or leaks.
4. Check transmission.
Table 3-13. Symptom Diagnosis
Checks Action