Check low-pressure fuel circuit

AR07.15-W-2000R

Check low-pressure fuel circuit

7.7.10



Checking

 Danger!

Risk of accident caused by vehicle starting off by itself when engine is running. Risk of injury caused by contusions and burns during starting procedure or when working near the engine as it is running

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

AS00.00-Z-0005-01A

Danger!

Risk of explosion caused by ignition of flammable products, risk of poisoning caused by inhaling fuel vapors or swallowing fuel as well as risk of injury to skin and eyes exposed to fuel.

No fire, sparks, open flames or smoking.
Pour fuels only into suitable and appropriately marked containers.

Wear protective clothing when handling fuel.

AS47.00-Z-0001-01A

1

Open engine hood and raise to vertical position

AR88.40-W-1000R

2

Check all fuel lines, connections and components of the fuel system for damage and leaktightness

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

3

Clean fouled components of the fuel system on the outside

4

Open end cover at fuel tank

5

Dewater fuel prefilter using a heated water separator and check fuel pre-filter insert for soiling

 Only on vehicles with code (K81) Fuel prefilter with heated water separator.
If necessary replace the fuel prefilter insert for a case of strong soiling.

AP47.20-W-0783R

6

Check fuel prefilter insert for soiling

 If necessary replace the fuel prefilter insert for a case of strong soiling.

AP47.20-W-0730R

7

Check the fuel filter element for soiling

 If necessary, replace the fuel prefilter element for a case of strong soiling.

AP47.20-W-0780R

8

Start engine, bring to normal operating temperature then switch off engine

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

9

Switch off ignition

10

Check low-pressure fuel circuit for signs of leaks

 Only check if the engine does not start properly.

AR07.15-W-2000-04R

*BE47.00-N-1003-01B



*BA47.25-N-1008-01J



*123589042118



*541589009100



*541589022100



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

AH07.15-N-1000-02F

11

Measure fuel pressure downstream of fuel filter

 Only measure in the case of vehicles with a poor engine performance.

AR07.15-W-2000-02R

*BE47.00-N-1001-01B



*123589042118



*541589009100



*541589022100

If the fuel pressure is too high:



Measure fuel return quantity at the fuel tank.

AR07.15-W-2000-03R

*BE47.00-N-1002-01B

If the fuel pressure is too low:



Measure fuel intake pressure upstream of fuel pump.

AR07.15-W-2000-05R

*BE47.00-N-1004-01B



*BA47.25-N-1008-01J



*541589009100



*617589042100



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

AH07.15-N-1000-02F

12

Close fuel tank cap

13

Start the engine and bleed the fuel system

 The fuel system is bled automatically.

14

Close engine hood

AR88.40-W-1000R

Number

Designation

Engine
900.9, 902.9, 904.9, 906.9, 924.9, 925.9, 926.9

BE47.00-N-1001-01B

Fuel pressure downstream of fuel filter

Idling speed

bar

4.3

Breakaway speed

bar

4.0 to 6.5

BE47.00-N-1002-01B

Fuel return quantity at fuel tank

Idling speed

l/min

0.9 to 2.0

Breakaway speed

l/min

2.0 to 10.5

BE47.00-N-1003-01B

Pressure drop in low pressure fuel circuit

Test pressure 5.0 bar / test period
5 min

bar

0

BE47.00-N-1004-01B

Fuel suction pressure upstream of fuel pump at filter supply

Breakaway speed

bar

-0.4 to -0.5

Number

Designation

Engine
900.9, 902.9, 904.9, 906.9, 924.9, 925.9, 926.9

BA47.25-N-1008-01J

Nut, feed and return line to fuel filter

Nm

45