JLG 450A_AJ Series II Service Manual - Manual (Page 142)

SECTION 3 - CHASSIS & TURNTABLE
3-102 – JLG Lift – 3121290
Ignition System Checks 1. Verify that the spark plugs are correct for use with LPG (R42LTS)
2. Check spark plugs. Remove and inspect plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Heavy deposits
3. Check ignition wires for the following items:
- Cracking
- Hardness
- Proper connections
Cooling System Checks Check engine thermostat for always being open or for the wrong heat range
Additional Check 1. Check transmission shift pattern. Refer to OEM Transmission Controls section Service Manual.
2. Check for dragging brakes.
Rough, Unstable, or Incorrect Idle, Stalling
DEFINITION: Engine runs unevenly at idle. If severe enough, engine or vehicle may shake. Engine idle speed may vary in RPM. Either condi-
tion may be severe enough to stall the engine.
Preliminary Check Refer to Important Preliminary Checks.
Sensor Checks 1. Check for silicon contamination from fuel or improperly used sealant. The sensor will have a white pow-
dery coating. The sensor will result in a high but false signal voltage (rich exhaust indication). ECM will
reduce the amount of fuel delivered to the engine causing a severe driveability problem.
2. Check the Heated Exhaust Gas Oxygen Sensor (HEGO) performance:
3. Check the Temperature Manifold Absolute Pressure (TMAP) sensor response and accuracy.
Fuel System Checks 1. Check for rich or lean symptom that causes the condition. Drive the vehicle at the speed of the com-
plaint. Monitoring the oxygen sensors will help identify the problem.
2. Check for a sticking mixer air valve.
3. Verify proper operation of the EPR.
4. Perform a cylinder compression test. Refer to Engine Mechanical in the Service Manual.
5. Check the LPR fuel pressure. Refer to the LPG Fuel System Diagnosis.
6. Check mixer module assembly for proper installation and connection.
Ignition System Checks 1. Check for proper ignition output voltage using spark tester J26792 or equivalent.
2. Verify spark plugs are correct for use with LPG (R42LTS)
3. Check spark plugs. Remove and inspect plugs for the following conditions:
- Wet plugs
- Cracks
- Wear
- Improper gap
- Burned electrodes
- Blistered insulators
- Heavy deposits
4. Check spark plug wires by connecting an ohmmeter to ends of each wire in question. If meter reads
over 30,000 ohms, replace wires.
Additional Checks Important: The LPG Fuel system works on a fumigation principle of fuel introduction and is more sensi-
tive to intake manifold leakage than a gasoline fuel supply system.
1. Check for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low throttle angle con-
trol command.
2.Check ECM grounds for being clean, tight, and in their proper locations.
3. Check battery cables and ground straps. They should be clean and secure. Erratic voltage may cause
faulty sensor readings resulting in poor idle quality.
Table 3-13. Symptom Diagnosis
Checks Action