Check low-pressure fuel circuit

AR07.15-W-2000RA

Check low-pressure fuel circuit

27.08.2020

Engine

457.9 in model 949

 Danger

Risk of explosion caused by fuel igniting, risk of poisoning caused by inhaling and swallowing fuel as well as risk of injury to eyes and skin caused by contactwith fuel.

No fires, sparks, open flames or smoking. Pour fuels into suitable and appropriately marked containers only.
Wear protective clothing when handling fuel.

AS47.00-Z-0001-01A

 Warning

Risk of accident from vehicle starting off by itself when engine running. Risk of injury (bruises and burns) resulting from working on the engine while it is being started or when it is running.

Secure vehicle to prevent it from starting off by itself. Wear closed and snug-fitting work clothes. Do not touch hot or rotating parts.

AS00.00-Z-0005-01A

Notes on possible sources of fault in the low-pressure fuel circuit

AH07.15-N-1000-02C



Check

1

Open engine hood and raise to vertical position

AR88.40-W-1000R

2

Clean assembly parts of the fuel system for soiling and dry.

3

Start engine and let it run for about 2 to 3 minutes at the maximum governed rpm, then stop the engine

4

Visually inspect all fuel lines, fittings, threaded connections and assembly parts of the fuel system

If damaged or leaky:



Replace any assembly part as necessary, seal connection and tighten threaded connection using the prescribed tightening torque.

5

Open cap on fuel tank

6

Dewater fuel prefilter and check fuel prefilter element; replace if necessary

Only for vehicles with code K81 (Fuel prefilter with heated water separator).



AP47.20-W-0783R

7

Remove fuel filter element and check



AP47.20-W-0790R

If there is severe contamination:



Replace fuel filter element.

8

Start engine and bring to operating temperature

 The fuel temperature in the fuel tank must be less than 40°C.

9

Switch off ignition

10

Check fuel low-pressure circuit for leaktightness

Only if the engine starts badly.

AR07.15-W-2000-04C

Pressure drop in low pressure fuel circuit

*BE47.00-N-1003-01D

 Banjo bolt, fuel line to fuel filter housing

*BA47.25-N-1004-01M

 Banjo bolt, fuel line to fuel heat exchanger

*BA47.25-N-1009-01M

 Banjo bolt, fuel line to solenoid valve of flame starting system/ banjo bolt for fuel filter housing

*BA47.25-N-1017-01M

 High-pressure hose

*123589042118

 Tester

*541589022100

 Adaptation parts

*541589009100

11

Measure fuel pressure downstream of fuel filter

Only for vehicles with poor engine performance.

AR07.15-W-2000-02C

Fuel pressure downstream of fuel filter

*BE47.00-N-1001-01D

 Banjo bolt, fuel line to fuel filter housing

*BA47.25-N-1004-01M

 Banjo bolt, fuel line to solenoid valve of flame starting system/ banjo bolt for fuel filter housing

*BA47.25-N-1017-01M

 High-pressure hose

*123589042118

 Tester

*541589022100

 Adaptation parts

*541589009100

If fuel pressure after measurement is too high:



Measure fuel return quantity at the fuel tank.

AR07.15-W-2000-03C

Fuel return quantity at fuel tank

*BE47.00-N-1002-01D

If fuel pressure after measurement is too low:



Measure fuel intake pressure upstream of fuel pump.

AR07.15-W-2000-05C

Fuel intake pressure upstream of fuel pump

*BE47.00-N-1004-01D

 Banjo bolt, fuel line to fuel heat exchanger

*BA47.25-N-1009-01M

 Tester

*617589042100

 Clamp

*000589403700

 Adaptation parts

*541589009100

12

Close fuel tank cap

13

Start the engine and bleed the fuel system

 The fuel system is bled automatically. Run the engine for approx. 1 minute.

If engine fails to start or only runs for a brief period:



Bleed fuel system.

AR47.00-W-1720S

14

Close engine hood

AR88.40-W-1000R

Fuel circuit check values

Number

Designation

ENGINE 457.9

BE47.00-N-1001-01D

Fuel pressure downstream of fuel filter

Idling speed

bar

1,8...2,8

Breakaway speed

bar

6,2...7,2

Fuel circuit check values

Number

Designation

ENGINE 457.9

BE47.00-N-1002-01D

Fuel return quantity at fuel tank

Idling speed

l/min

1,1...1,5

Breakaway speed

l/min

2,2...2,8

Fuel circuit check values

Number

Designation

ENGINE 457.9

BE47.00-N-1003-01D

Pressure drop in low pressure fuel circuit

Test pressure 5.0 bar / test period 5 min.

bar

0

Fuel circuit check values

Number

Designation

ENGINE 457.9

BE47.00-N-1004-01D

Fuel intake pressure upstream of fuel pump

Breakaway speed

bar

–0,30...–0,15

 Fuel lines/hoses

Number

Designation

ENGINE 457.9

BA47.25-N-1004-01M

Banjo bolt, fuel line to fuel filter housing

Nm

50

 Fuel lines/hoses

Number

Designation

ENGINE 457.9

BA47.25-N-1009-01M

Banjo bolt, fuel line to fuel heat exchanger

Nm

50

 Fuel lines/hoses

Number

Designation

ENGINE 457.9

BA47.25-N-1017-01M

Banjo bolt, fuel line to solenoid valve of flame starting system/ banjo bolt for fuel filter housing

Nm

15