JLG 660SJ Service Manual - Manual (Page 142)

SECTION 3 - CHASSIS & TURNTABLE
3-98 – JLG Lift – 3121298
Ignition System Checks Note: LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating conditions. If a prob-
lem is reported on LPG and not gasoline, do not discount the possibility of a LPG only ignition system failure and test the system accordingly.
2 Check for the proper ignition voltage output with J 26792 or the equivalent.
2 Verify that the spark plugs are correct for use with LPG (R42LTS)
2 Check for faulty spark plug wires
2 Check for fouled spark plugs.
Additional Check 2 Check for manifold vacuum or air induction system leaks
2 Check the generator output voltage.
Backfire
DEFINITION: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise.
Preliminary Check 2 Refer to Important Preliminary Checks.
Ignition System Checks Important! LPG, being a gaseous fuel, requires higher secondary ignition system voltages for the equivalent gasoline operat-
ing conditions. The ignition system must be maintained in peak condition to prevent backfire.
2 Check for the proper ignition coil output voltage using the spark tester J26792 or the equivalent.
2 Check the spark plug wires by connecting an ohmmeter to the ends of each wire in question. If the meter reads over 30,000 ohms, replace the
wires.
2 Check the connection at each ignition coil.
2 Check for deteriorated spark plug wire insulation.
2 Check the spark plugs. The correct spark plugs for LPG are (R42LTS)
2 Remove the plugs and inspect them for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
Engine Mechanical Check Important! The LPG Fuel system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than a
gasoline fuel supply system.
2 Check the engine for the following:
- Improper valve timing
- Engine compression
- Manifold vacuum leaks
- Intake manifold gaskets
- Sticking or leaking valves
- Exhaust system leakage
2 Check the intake and exhaust system for casting flash or other restrictions.
Fuel System Checks 2 Perform a fuel system diagnosis. Refer to LPG Fuel System Diagnosis.
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 2 Refer to Important Preliminary Checks.
2 Refer to the LPG Fuel system OBD System Check
2 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
2 Remove the air filter and check for dirt or restriction.
2 Check the vehicle transmission Refer to the OEM transmission diagnostics.
Table 3-12. Symptom Diagnosis
Checks Action