SECTION 3 - CHASSIS, PLATFORM & SCISSOR ARMS
3-90 – JLG Lift – 3121642
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.
• Check for the proper ignition voltage output with J 26792 or the equivalent.
• Verify that the spark plugs are correct for use with LPG (R42LTS).
• Check for faulty spark plug wires.
• Check for fouled spark plugs.
Additional Check • Check for manifold vacuum or air induction system leaks.
• 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 • Refer to Important Preliminary Checks.
Ignition System Checks Important: LPG, being a gaseous fuel, requires higher secondary ignition system voltages for the equivalent gasoline operating conditions.
The ignition system must be maintained in peak condition to prevent backfire.
• Check for the proper ignition coil output voltage using the spark tester J26792 or the equivalent.
• 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.
• Check the connection at each ignition coil.
• Check for deteriorated spark plug wire insulation.
• Check the spark plugs. The correct spark plugs for LPG are (R42LTS).
• Remove the plugs and inspect them for the following conditions:
- Wet plugs
- Cra cks
- Wear
- Impro pe r g ap
- Burned electrodes
- Heav y de po si ts
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.
• Check the engine for the following:
- Impro pe r v al ve ti mi ng
- Engi ne c omp re ss io n
- Mani fol d va cu um le aks
- Int ake ma ni fo ld gas ke ts
- Stick in g o r lea king va lv es
- Exhaus t sy ste m l eak age
• Check the intake and exhaust system for casting flash or other restrictions.
Fuel System Checks • 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 • 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.
Table 3-14. Symptom Diagnosis
Checks Action
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