JLG 400S Service And Maintenance Manual page 211

Checks
Fuel System Checks
Sensor Checks
Exhaust System Checks
Engine Mechanical Check
Additional Check
DEFINITION: Fuel economy, as measured by refueling records, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously
shown by an by refueling records.
Preliminary Checks
Fuel System Checks
Sensor Checks
Ignition System Checks
Cooling System Checks
3121671
Table 3-14. GM Engine Symptom Diagnosis
² Check for a restricted fuel filter, contaminated fuel, or improper fuel pressure. Refer to LPG Fuel System Diagnosis.
² Check for the proper ignition output voltage with the spark tester J 26792 or the equivalent.
² Check for proper installation of the mixer module assembly.
² Check all air inlet ducts for condition and proper installation.
² Check for fuel leaks between the LPR and the mixer.
² Verify that the LPG tank manual shut-off valve is fully open.
² Verify that liquid fuel (not vapor) is being delivered to the LPR.
² Check the Heated Exhaust Gas Oxygen Sensor (HEGO) for contamination and performance. Check for proper operation of the MAP sensor.
² Check for proper operation of the TPS sensor.
² 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.
Check the engine for the following:
² Engine compression
² Valve timing
² Improper or worn camshaft. Refer to Engine Mechanical in the Service Manual.
² Check the ECM grounds for being clean, tight, and in their proper locations.
² Check the generator output voltage.
² If all procedures have been completed and no malfunction has been found, review and inspect the following items:
² Visually and physically, inspect all electrical connections within the suspected circuit and/or systems.
² Check the scan tool data.
Poor Fuel Economy
² Refer to Important Preliminary Checks.
² Check the air cleaner element (filter) for dirt or being plugged.
² Visually (Physically) check the vacuum hoses for splits, kinks, and proper connections.
² Check the operators driving habits for the following items:
- Is there excessive idling or stop and go driving?
- Are the tires at the correct air pressure?
- Are excessively heavy loads being carried?
- Is their often rapid acceleration?
² Suggest to the owner to fill the fuel tank and to recheck the fuel economy.
² Suggest that a different operator use the equipment and record the results.
² Check the LPR fuel pressure. Refer to LPG Fuel System Diagnosis.
² Check the fuel system for leakage.
² Check the Temperature Manifold Absolute Pressure (TMAP) sensor.
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
² Check the ignition wires for the following items:
- Cracking
- Hardness
- Proper connections
² Check the engine thermostat for always being open or for the wrong heat range
SECTION 3 - CHASSIS & TURNTABLE
Action
3-153