Kubota WG1605-E3 Diagnostic Manual page 36

WG1605-G-E3,WG1605-L-E3,WG1605-GL-E3, DM
Checks
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
Sensor Checks
Fuel System Checks
Ignition System Checks
Additional Checks
Engine Mechanical Check
Rough, Unstable, or Incorrect Idle, Stalling
• Refer to Important Preliminary Checks.
• Check for silicon contamination, from fuel or improperly used sealant. The sensor will have a white
powdery coating. 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.
• Check the Heated Exhaust Gas Oxygen Sensor (HEGO) performance:
• Check the Temperature Manifold Absolute Pressure (TMAP) sensor, response and accuracy.
• Check for rich or lean symptom, that causes the condition. Drive the vehicle, at the speed of the
complaint. Monitoring the oxygen sensors, will help identify the problem.
• Check for a sticking mixer air valve.
• Perform a cylinder compression test. Refer to Engine Mechanical in the Service Manual.
• Check the DSR fuel pressure. Refer to the LPG / Natural Gas Fuel System Diagnosis.
• Check mixer module assembly, for proper installation and connection.
• Check for the proper ignition output voltage, using the spark tester.
• Verify that the spark plugs are correct, for use with LPG / natural gas.
• Check the spark plugs. Remove the plugs and inspect them for the following conditions:
– Wet plugs
– Cracks
– Wear
– Improper gap
– Burned electrodes
– Blistered insulators
– Heavy deposits
IMPORTANT
• The LPG / Natural Gas Fuel system works on a fumigation principle, of fuel introduction,
and is more sensitive to intake manifold leakage, than the gasoline fuel supply system.
• Check for vacuum leaks. Vacuum leaks can cause a higher than normal idle, and low throttle angle
control command.
• Check the ECM grounds, for being clean, tight, and in their proper locations.
• Check 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.
• Check the engine for the following:
– Broken motor mounts
– Improper valve timing
– Low compression
– Bent pushrods
– Worn rocker arms
– Broken or weak valve springs
– Worn camshaft lobes
1-26
Action
ECM SYSTEM
KiSC issued 12, 2016 A