Man 3779

Rail pressure: Leakage due to quantity compensation 3779

Monitoring for leakage in high-pressure hydraulic system System reaction: High-pressure side leaking, engine stops, lack of power, risk of fire. Limiting: 130-150 mg/stroke

SPN 3779 RAIL PRESSURE: LEAKAGE DUE TO QUANTITY COMPENSATION Fault display:

Central fault lamp flashes red whilst driving and when stationary, stop indication on display (priority 1)

Monitoring strategy:

Monitoring for leakage in high-pressure hydraulic system

Effect of fault:

Engine can stop, lack of power, danger of fire. Limiting: D08: 100 mg/stroke, D20: 130-150 mg/stroke, D26: 180 mg/stroke

Refer to the diagrams for the vehicle in question Testing

Measurement

Correcting the fault •

Fuel Fuel syst system em

Chec Check k acc accor ordi ding ng to hydr hydrau auli licc tes testt ste step p lis listt

Metering unit (MProp)

Resistance measurement between pin A08 and A10 Nominal value: 2.5 – 4.5 Ω

• •

•

Rail pressure sensor

Check the plug connection on the sensor for loose contact

See hydraulic test step list Check lines Check plug connectors Repair or renew the connector Renew rail pressure sensor

•

hydraulic test step list

1st Check the electrical cables and plugs to the fuel metering unit and to the rail pressure step sensor Renew the fuel metering unit if a high rail pressure output value of 10-14% is 2nd recorded at idling speed with the engine warm (cooling water min. 70°C). Re-install step the original fuel metering unit and continue from step 3 if there is no value change to < 6%. *) Measure the total leakage volume of the injectors and the pressure limiting valve. Check the PLV for leaks if the volume is too high. (PLV must be leak-tight.) Renew 3rd the PLV if it is leaking and repeat the total leakage volume measurement. Check the step rail pressure controller output value is < 6%. Measure the individual leakage of the injectors if the PLV is not leaking. 4th Now renew the fuel metering unit if the rail pressure controller output value was step measured between 6 and 10 % in test step 2 5th Renew the rail pressure sensor (only with SPN 3781) step 6th Measure the delivery volume of the high-pressure pump. Renew the HP pump if the step volume is too low. Contact the relevant technical department if the volume is OK