JLG 740A, Service And Maintenance Manual

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SECTION 3 - CHASSIS & TURNTABLE
3121160 – JLG Lift – 3-147
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 System in
the GM Base Engine Service Manual
Additional Checks
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
- 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 3-13. Symptom Diagnosis
Checks Action