JLG 4394RT Service Manual - Manual (Page 160)

SECTION 3 - CHASSIS, PLATFORM & SCISSOR ARMS
3-124 – JLG Lift – 3121249
Exhaust System Checks • 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
• Check for possible plugged catalytic converter. Refer to Restricted Exhaust System Diagnosis or Exhaust Sys-
tem in the GM Base Engine Service Manual.
Cuts Out, Misses
DEFINITION: A surging or jerking that follows engine speed, usually more pronounced as the engine load increases which is not normally felt above 1500
RPM. The exhaust has a steady spitting sound at idle, low speed, or hard acceleration for the fuel starvation that can cause the engine to cut-out.
Preliminary Checks
• Refer to Important Preliminary Checks.
Ignition System Checks • Start the engine.
• Wet down the secondary ignition system with water from a spray bottle, and look/listen for arcing or misfiring
as you apply water.
• Check for proper ignition output voltage with spark tester J 26792.
• Check for a cylinder misfire.
• Verify that the spark plugs are correct for use with LPG (R42LTS).
• Remove the spark plugs in these cylinders and check for the following conditions:
- Insulation cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
• Visually/Physically inspect the secondary ignition for the following:
- Ignition wires for arcing, cross-firing and proper routing
- Ignition coils for cracks or carbon tracking
Engine Mechanical Checks • Perform a cylinder compression check.
• Check the engine for the following:
- Improper valve timing
- Bent pushrods
110
- Worn rocker arms
- Worn camshaft lobes
- Broken or weak valve springs
• Check the intake and exhaust manifold passages for casting flash.
Fuel System Checks • Check the fuel system - plugged fuel filter, low fuel pressure, etc. Refer to LPG Fuel System Diagnosis.
• Check the condition of the wiring to the low pressure lock-off solenoid.
Additional Check Check for Electromagnetic Interference (EMI).
• EMI on the reference circuit can cause a missing condition.
• Monitoring the engine RPM with a scan tool can detect an EMI.
• A sudden increase in the RPM with little change in the actual engine RPM, indicates EMI is present.
• If the problem exists, check the routing of the secondary wires and the ground circuit.
Table 3-16. Symptom Diagnosis
Checks Action