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Fault diagnosis in connection with long starting times, diesel

Symptom: Difficult to start engine. Reduced driveability.

Fault diagnosis in connection with long starting times, diesel


Background

In connection with long starting times and impaired drivability when the car has been parked overnight or on a hill, the fuel system should be tested for leakage.

Symptom description

Difficult to start engine. Reduced driveability.



Parts required

47 73 354 Hose for return fuel line (by the metre)

95 44 271 T-pieces

2 x 2 copper washers for the fuel line connection on the pump

95 42 929 O-ring for fuel bridge

95 42 903 Injector seal

Tool

83 93 514 Charge pressure gauge

83 95 584 Adapter kit, leakage test, fuel lines

30 14 883 Pressure/vacuum pump

30 07 739 Hose pinch-off pliers

30 31 069 Nipple, bleeding equipment

88 19 096 Bleeding equipment

83 95 261 Fuel line tool

83 96 400 Adapter, leakage test

Procedure

Warning

Fault diagnosis being carried out on the fuel lines involves dismantling the car's fuel system. The following points must therefore be observed while taking this action:



• Ensure good ventilation! If there is approved ventilation for extraction of fuel fumes then this must be used.

• Wear protective gloves! Prolonged exposure of the hands to fuel can cause irritation of the skin.

• Have a fire extinguisher class BE at hand! Be aware of the risk for sparks, i.e. in connection with breaking circuits, short-circuiting, etc.

• Absolutely no smoking!


The following leakage tests are described:

A) The fuel bridge return lines

B) Suction line to tank

C) Return lines

A) The fuel bridge return lines


1. Remove the engine cover.

2. Remove the lower end (common) of the hose branch from the banjo nipple at the injection pump suction connection. Check the end of the hose for damage and cracks. Connect the hose to the 30 14 883 Pressure/vacuum pump .

Important

First, check for leaks in the pressure/vacuum pump and hoses in order to avoid unreliable fault diagnosis results.



3. Pump to achieve a negative pressure of -0.9 bar, wait approx. 10 minutes and check to see that the negative pressure is maintained.

4. If a leak is detected, each individual return hose should be checked from its respective fuel bridge as follows:

5. Remove the charge air pipe and plug the hoses.


6. Undo the upper part of the throttle body and move aside. Undo the hose branch from the injector connection bridges.

Note

If black engine oil comes from the return hoses this implies that there is a leak from the gaskets between the injectors and fuel bridges. If black oil is also found when changing the fuel filter this is probably due to the same fault.

Check the colour of the fuel by opening the draining screw on the fuel filter. The reinforced rubber hoses in the branching for the return of excess fuel are usually damaged in connection with removal due to sharp barbs on the plastic nipples.

Therefore, change the hoses if they have been removed. Spare hose is stocked by the metre, approx. 75 cm is needed. The plastic nipples may also need changing.


7. Connect 30 14 883 Pressure/vacuum pump in turn to the four nipples on the fuel bridges. Create a negative pressure of -0.9 bar. The pressure should remain for approx. 10 min. If the pressure changes, all four O-rings and sealing sleeves between the injector and the fuel bridge should be changed. See Basic engine, diesel, Fuel system, Fuel bridges.


8. Fit the new fuel return hoses onto the fuel bridges. Check the T-pieces that connect the fuel return hoses for damage, cracks, etc. Change if necessary.


9. Carry out a new leakage test by connecting the vacuum pump to the lower common hose to the inlet pipe on the fuel pump as described in point A

10. Fit the hose to the banjo nipple at the injection pump suction connection.

11. Fit the upper part of the throttle body.

12. Remove the plugs and fit the charge air pipe.


B) Suction line to tank


By lifting the front assembly of the car (alternatively parking on a slope) the fuel system sensitivity to leaks increases. In connection with fault diagnosis we therefore recommend having the front assembly in a raised position.

Leaks in these situations are usually so small that the passage of fuel cannot be perceived. On the other hand air passage is obtained, which in this case supplies air to the fuel system.


1. Connect 83 93 514 Charge pressure gauge and 83 95 584 Adapter kit, leakage test, fuel lines with a hose to the service outlet on the suction line. (Suspend the pressure gauge, for example from the bonnet lock as illustrated).


2. To be able to discover leaks faster, lift the front of the car approx. 70 cm. Use axle stands.


3. Start the engine and let it run a few minutes. Stop the engine and read the pressure gauge, which due to the angle of the car and fuel quantity in the tank reads between -0.04 - 0.08 bar. Too low a vacuum at idling speed (lower than -0.20 bar) can indicate a blocked filter or restricted suction lead. Leave the car stationary for approx. 2 hours. The pressure reading should remain the same.

4. A loss of negative pressure indicates a leak in the suction line in one of the following locations: (investigate and rectify in the following order).

4.1) The suction line banjo connection to the injection pump.

-Check the sealing surfaces against the copper gaskets (on pump, banjo nipple and hollow screw respectively).

-Change copper gaskets on banjo connection.

-High standards of cleanliness (dirt particles must not occur in connection with these surfaces).

4.2) Fuel filter connections, cover or housing.

If the leak persists after rectifying as in 4.1, check that couplings, connections and filter gasket are not leaking.

4.3) Connection to fuel tank and damaged fuel line from tank to filter

If the leak persists after carrying out tests and measures, the leak must be between the tank connection and the connection to the fuel filter. Check the connection to the tank and the supply line to the fuel filter. See To remove, Fuel tank . If the tank is removed, carry out the leak test according to C.

5. On completion we recommend checking the fault diagnosis and repair as follows: Warm up the car and park it with the front raised, on a hill or on axle stands, for 12 hours. Start the engine, which should now start without any delay.


C) Return lines



1. Separate the return hose quick coupling using 83 95 261 Tool, fuel line and fit 83 95 584 Adapter kit, leakage test, fuel lines and 83 96 400 Adapter, leakage test

2. Connect 83 93 514 Charge pressure gauge with coupling 83 95 592 to the T-nipple's service outlet. Start the engine and read the pressure gauge. The pressure must not exceed 1.0 bar. Too high a pressure indicates a blockage on the return side. Switch off the engine.


3. Check the return line for kinks. Check the ejector in the fuel level sensor for impurities. See To remove under Fuel level sensor .


4. Put the ignition in the OFF position, undo the pressure gauge connection, remove the T-nipple and connect the return line. Have a cloth nearby in case of fuel spillage.


Bleeding the fuel lines

To speed up bleeding the fuel system when air has entered, for example while changing a filter or when the fuel lines on the inlet side have been removed, use the method below.


1. Connect 30 31 069 Nipple, bleeding equipment to 88 19 096 Bleeding equipment or the equivalent and start the suction equipment.


2. Remove the end cap and connect the nipple to the service outlet on the fuel pump feed line.

3. Suck until a constant flow of fuel is seen in the suction line to the brake-bleeding tool.

4. Remove the bleeder nipple from the service outlet while the equipment is running (this avoids fuel spills and air entering the system).

5. Put the protective cap onto the service outlet.


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