JLG 4394RT Service Manual - Manual (Page 164)

SECTION 3 - CHASSIS, PLATFORM & SCISSOR ARMS
3-128 – JLG Lift – 3121249
Engine Mechanical Check • 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
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
Refer to Important Preliminary Checks.
Sensor Checks • Check Heated Exhaust Gas Oxygen Sensor (HEGO) performance.
Fuel System Checks • Check for Rich or Lean symptom that causes the condition. Drive the vehicle at the speed of the complaint.
Monitoring the oxygen sensors will help identify the problem.
• Check the fuel pressure while the condition exists. Refer to LPG Fuel System Diagnosis.
• Verify proper fuel control solenoid operation.
• Verify that the LPG manual shut-off valve is fully open.
• Check the in-line fuel filter for restrictions.
Ignition System Checks • Check for the proper ignition output voltage using the spark tester J26792 or the equivalent.
• Verify that the spark plugs are correct for use with LPG (R42LTS).
• 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
Additional Check • Check the ECM grounds for being clean, tight, and in their proper locations.
• Check the generator output voltage.
• Check the vacuum hoses for kinks or leaks.
• Check Transmission.
Table 3-16. Symptom Diagnosis
Checks Action