Service Manual

SECTION 3 - CHASSIS & TURNTABLE
3121202 – JLG Lift – 3-119
Ignition System Checks
² Verify that the spark plugs are correct for use with LPG (R42LTS)
² Check the spark plugs. Remove the plugs and inspect them for the following conditions:
- Wet plugs
- Cr ack s
- Wea r
- Improper gap
- Burned electrodes
- Heav y deposits
² Check the ignition wires for the following items:
- Cr ack ing
- Hard nes s
- Proper connections
Cooling System Checks ² Check the engine thermostat for a lways bei ng o pen or for the wrong heat range
Additional Check
² Check the transmission shift pattern. Refer to the OEM Transmission Controls section the Service Manual.
² Check for dragging brakes.
Rough, Unstable, or Incorrect Idle, Stalling
DEFINITION: The engine runs unevenly at idle. If severe enough, the engine or vehicle may shake. The engine idle speed may vary i n R P M . E i t h e r c o n d i t i o n
may be severe enough to stall the engine.
Preliminary Check Refer to Important Preliminary Checks.
Sensor Checks
²Check for silicon contamination from fuel or improperly used sealant. The sensor will have a white powdery coat-
ing. The sensor will result in a high but false signal voltage (rich exhaust indication). The ECM will reduce the amount
of fuel delivered to the engine causing a severe driveability problem.
²Check the Heated Exhaust Gas Oxygen Sensor (HEGO) performance:
²Check the Temperature Manifold Absolute Pressure (TMAP) sensor response and accuracy.
Fuel System Checks
²Check for rich or lean symptom that causes the condition. Drive the vehicle at the speed of the complaint. Monitor-
ing the oxygen sensors will help identify the problem.
²Check for a sticking mixer air valve.
²Verify proper operation of the EPR.
²Perform a cylinder compression test. Refer to Engine Mechanical in the Service Manual.
²Check the LPR fuel pressure. Refer to the LPG Fuel System Diagnosis.
²Check mixer module assembly for proper installation and connection.
Ignition System Checks
²Check for the proper ignition output voltage using the spark tester J26792 or the equivalent.
² Verify that the spark plugs are correct for use with LPG (R42LTS)
²Check the spark plugs. Remove the plugs and inspect them for the following conditions:
- Wet plugs
- Cr ack s
- Wea r
- Improper gap
- Burned electrodes
- Blistered insulators
- Heav y deposits
²Check 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.
Additional Checks
Important: The LPG Fuel system works on a fumigation principle of fuel introduction and is more sensitive to intake
manifold leakage than the gasoline fuel supply system.
²Check for vac uum leaks . Vacuum l eaks can cause a higher than normal idle and low throttle angle control com-
mand.
²Check the ECM grounds for being clean, tight, and in their proper locations.
²Check the battery cables and ground straps. They should be clean and secure. Erratic voltage may cause all sensor
readings to be skewed resulting in poor idle quality.
Table 3-12. Symptom Diagnosis
Checks Action