Fault Phenomenon: Caterpillar 789D mining truck engine speed unstable, occasionally stalls automatically, reports fuel system fault.

Troubleshooting Process:
– Checked metering unit: high-pressure pump metering valve (IMV) stuck.
– Checked fuel: fuel contained gum or impurities.
– Checked filter: fuel filter poor filtration.
– Checked wiring: metering unit coil resistance abnormal.

Root Cause: The high-pressure common rail pump metering unit is stuck due to gum deposits in the fuel, causing slow or stuck spool movement and inaccurate injection quantity control.

Required Parts: Replace high-pressure fuel pump metering unit or pump assembly.