JLG 600SJ Service And Maintenance Manual page 170

SECTION 3 - CHASSIS & TURNTABLE
Checks
Engine Mechanical Check
DEFINITION: The engine has a power variation under a steady throttle or cruise. The vehicle feels as if it speeds up and slows down with no change in the
accelerator pedal.
Preliminary Checks
Sensor Checks
Fuel System Checks
Ignition System Checks
Additional Check
3-120
Table 3-12. Symptom Diagnosis
² Check the 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
Refer to Important Preliminary Checks.
² Check Heated Exhaust Gas Oxygen Sensor (HEGO) performance.
² Check for Rich or Lean symptom that causes the condition. Drive the vehicle at the speed of the complaint. Moni-
toring the oxygen sensors will help identify the problem.
² Check the fuel pressure while the condition exists. Refer to LPG Fuel System Diagnosis.
² Verify proper fuel control solenoid operation.
² Verify that the LPG manual shut-off valve is fully open.
² Check the in-line fuel filter for restrictions.
² Check for the proper ignition output voltage using the spark tester J26792 or the equivalent.
² Verify that the spark plugs are correct for use with LPG (R42LTS)
² Check the spark plugs. Remove the plugs and inspect them for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
- Check the Crankshaft Position (CKP) sensor.
² Check the ECM grounds for being clean, tight, and in their proper locations.
² Check the generator output voltage.
² Check the vacuum hoses for kinks or leaks.
² Check Transmission
Action
– JLG Lift – 3121202