JLG 680S Service Manual - Manual (Page 189)

SECTION 3 - CHASSIS & TURNTABLE
3121234 – JLG Lift – 3-141
Lack of Power, Sluggishness, or Sponginess
DEFINITION: The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal.
Preliminary Checks Refer to Important Preliminary Checks.
Refer to the LPG Fuel system OBD System Check
Compare the customer's vehicle with a similar unit. Make sure the customer has an actual problem. Do not compare
the power output of the vehicle operating on LPG to a vehicle operating on gasoline as the fuels do have different drive
feel characteristics
Remove the air filter and check for dirt or restriction.
Check the vehicle transmission Refer to the OEM transmission diagnostics.
Fuel System Checks Check for a restricted fuel filter, contaminated fuel, or improper fuel pressure. Refer to LPG Fuel System Diagnosis.
Check for the proper ignition output voltage with the spark tester J 26792 or the equivalent.
Check for proper installation of the mixer module assembly.
Check all air inlet ducts for condition and proper installation.
Check for fuel leaks between the LPR and the mixer.
Verify that the LPG tank manual shut-off valve is fully open.
Verify that liquid fuel (not vapor) is being delivered to the LPR.
Sensor Checks Check the Heated Exhaust Gas Oxygen Sensor (HEGO) for contamination and performance. Check for proper opera-
tion of the MAP sensor.
Check for proper operation of the TPS sensor.
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.
Engine Mechanical Check Check the engine for the following:
Engine compression
Valve timing
Improper or worn camshaft. Refer to Engine Mechanical in the Service Manual.
Additional Check Check the ECM grounds for being clean, tight, and in their proper locations.
Check the generator output voltage.
If all procedures have been completed and no malfunction has been found, review and inspect the following items:
Visually and physically, inspect all electrical connections within the suspected circuit and/or systems.
Check the scan tool data.
Poor Fuel Economy
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 Refer to Important Preliminary Checks.
Check the air cleaner element (filter) for dirt or being plugged.
Visually (Physically) check the vacuum hoses for splits, kinks, and proper connections.
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?
Suggest to the owner to fill the fuel tank and to recheck the fuel economy.
Suggest that a different operator use the equipment and record the results.
Fuel System Checks Check the LPR fuel pressure. Refer to LPG Fuel System Diagnosis.
Check the fuel system for leakage.
Sensor Checks Check the Temperature Manifold Absolute Pressure (TMAP) sensor.
Table 3-10. Symptom Diagnosis
Checks Action