Kubota WG1605-E3, Diagnostic Manual

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ECM SYSTEM
WG1605-G-E3,WG1605-L-E3,WG1605-GL-E3, DM
1-16
Rough, Unstable or Incorrect Idle or Stalling
Checks Action
DEFINITION: The engine runs unevenly at idle. If severe enough, the engine or vehicle may shake. The engine idle speed may vary in RPMs.
Either condition may be severe enough to stall the engine.
Preliminary Check • Refer to Important Preliminary Checks.
Sensor 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 drivability
problem.
• Check the Heated Exhaust Gas Oxygen Sensor (HEGO) performance.
• Check the Temperature Manifold Absolute Pressure (TMAP) sensor response and accuracy.
Fuel System Checks
• Check for rich or lean symptoms that causes the condition. Drive the vehicle at the speed of the
complaint. Monitoring the oxygen sensors will help identify the problem.
• Verify proper operation of the injectors.
• Perform a cylinder compression test. Refer to Engine Mechanical in the Service Manual.
• Check the fuel Rail pressure. Refer to the Gasoline Fuel System Diagnosis.
• Check injector electrical connections.
Ignition System Checks
• Check for the proper ignition output voltage using the spark tester.
• Verify that the spark plugs are correct.
• 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
Additional Checks
• 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.
Engine Mechanical Check
• 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
KiSC issued 12, 2016 A