Service Manual Instruction Manual

SECTION 3 - CHASSIS & TURNTABLE
3-100 – JLG Lift – 3121616
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 in RPM. Either condition 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 coating. The sen so r wil l r es ul t i n a
high but false signal voltage (rich exhaust indication). The ECM will reduce the amount of fuel delivered to the engine causing a severe drive-
ability problem.
²Check the Heated Exhaust Gas Oxygen Sensor (HEGO) performance:
²Check the Temperature Manifold Absolute Pressure (TMAP) sensor response and accuracy.
Fu el Sy st em Ch ec ks ²C he ck f or ric h or lean sy mpt om th at cau se s the condition. Drive the vehicle at the speed of the complaint. Monitoring 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:
- We t p lu gs
- Crack s
- We ar
- Improper gap
- Burned electrodes
- Bl is te re d i ns ul at or s
- Heavy deposits
²Ch eck t he s pa rk p lug wir es by co nn ec t in g a n o hm me te r t o t he 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 vacuum leaks. Vacuum leaks can cause a higher than normal idle and low throttle angle control command.
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.
En gin e Me cha ni c al Ch ec k ² Ch ec k t he e ng ine for th e fo llo wi ng :
- Br oke n mo to r m oun ts
- Im pr op er va lve ti min g
- Lo w c om pr es si on
- Be nt pu shr od s
- Wo rn rocke r a rm s
- Br oke n or we ak va lv e s pr in gs
- Wo rn ca ms ha f t l ob es
Surges/Chuggles
DEFINITION: The engine has a power variation under a steady throttle or cruise. The vehicle feels as if it speeds up and slows d ow n w it h no ch an ge i n t he ac ce le ra to r p ed al .
Preliminary Checks Refer to Important Preliminary Checks.
Sensor Checks ² Check Heated Exhaust Gas Oxygen Sensor (HEGO) performance.
Table 3-11. Symptom Diagnosis
Checks Action