JLG 450A_AJ Series II Service Manual - Manual (Page 141)

SECTION 3 - CHASSIS & TURNTABLE
3121290 – JLG Lift – 3-101
Lack of Power, Sluggishness, or Sponginess
DEFINITION: Engine delivers less than expected power. There is little or no increase in speed when partially applying accelerator pedal.
Preliminary Checks 1. Refer to Important Preliminary Checks.
2. Refer to LPG Fuel system OBD System Check
3. Compare customer's vehicle with a similar unit. Make sure customer has an actual problem. Do not
compare power output of vehicle operating on LPG to a vehicle operating on gasoline as fuels have dif-
ferent drive feel characteristics.
4. Remove air filter and check for dirt or restriction.
5. Check vehicle transmission Refer to OEM transmission diagnostics.
Fuel System Checks 1. 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.
3. Check for proper installation of the mixer module assembly.
4. Check all air inlet ducts for condition and proper installation.
5. Check for fuel leaks between the LPR and the mixer.
6. Verify that the LPG tank manual shut-off valve is fully open.
7. Verify that liquid fuel (not vapor) is being delivered to the LPR.
Sensor Checks 1. Check Heated Exhaust Gas Oxygen Sensor (HEGO) for contamination and performance.
2. Check proper operation of MAP sensor.
3. Check proper operation of TPS sensor.
Exhaust System Checks Check exhaust system for a possible restriction:
- Inspect exhaust system for damaged or collapsed pipes.
- Inspect 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 1. Check ECM grounds for being clean, tight, and in their proper locations.
2. Check generator output voltage.
3. If all procedures have been completed and no malfunction has been found, review and inspect the fol-
lowing items:
- Visually and physically inspect all electrical connections within suspected circuit and/or systems.
- Check scan tool data.
Poor Fuel Economy
DEFINITION: Economy is noticeably lower as shown by refueling records.
Preliminary Checks 1. Refer to Important Preliminary Checks.
2. Check air cleaner element (filter) for dirt or restriction.
3. Visually (Physically) check vacuum hoses for splits, kinks, and proper connections.
4. Check operator driving habits for the following items:
- Is there excessive idling or stop and go driving?
- Are tires at correct air pressure?
- Are excessively heavy loads being carried?
- Is there often rapid acceleration?
5. Suggest to owner to fill fuel tank and recheck fuel economy.
6. Suggest a different operator use equipment and record results.
Fuel System Checks 1. Check LPR fuel pressure. Refer to LPG Fuel System Diagnosis.
2. Check fuel system for leakage.
Sensor Checks Check Temperature Manifold Absolute Pressure (TMAP) sensor.
Table 3-13. Symptom Diagnosis
Checks Action