Service Manual Instruction Manual

SECTION 3 - CHASSIS & TURNTABLE
3-98 – JLG Lift – 3121616
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:
- We t p lu gs
- Crack s
- We ar
- 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:
- Im pr op er va lv e t im in g
- En gi ne co mp re ss io n
- Ma ni fo ld va cuu m le ak s
- In ta ke ma ni fo ld ga sk et s
- St ic ki ng or lea ki ng va lve s
- Ex ha us t sy st em le akage
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
DEF INI TIO N: T he en gi ne de li ve rs les s t han ex pe c te d p ower. Th ere is li tt le or n o incr ea se in sp e ed wh en pa r ti al ly ap p ly in g t he 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 3-11. Symptom Diagnosis
Checks Action