Checking vacuum at high-pressure fuel pump (venturi nozzle)

⇒ 2 Safety information

⇒ 3.1 Rules for cleanliness

Observe instructions for working on fuel system ⇒ 23 – Mixture preparation - injection

Special tools and workshop equipment required

• Pressure gauge - VAS 6551-
• Hose adapter - VAS 6551/1-
• Hose adapter - VAS 6551/2-
• Not illustrated
• Hose adapter - VAS 6551/3-
• Hose adapter - VAS 6551/4-
• Vehicle diagnostic tester

Test conditions:

Checking delivery pressure of fuel pump ⇒ Fuel supply system; Rep. gr. 20

Checking delivery pressure in fuel return line ⇒ Fuel supply system; Rep. gr. 20

Checking delivery rate of fuel pump ⇒ Fuel supply system; Rep. gr. 20

• Battery voltage at least 12.5 V
• Fuel filter OK.
• Ignition off

Checking

• Remove engine cover panel ⇒ 3 Engine cover panel.

• Carefully release fuel return line at high-pressure pump.
• Carefully pull fuel return line out of high-pressure pump.

• Connect free end of fuel return line to hose adapter - VAS 6551/3-, and hold it into a ≤ 3 litre measuring container -3-.

• Connect pressure tester - VAS 6551- with hose adapter - VAS 6551/4- from connection -A- to high-pressure pump.
• Close shut-off tap of pressure tester - VAS 6551- -A- + -B- and open -C-.

• Connect free connection -arrow- at high-pressure pump to hose adapter - VAS 6550/4-.

• Ask a second mechanic for assistance.
• Switch on pressure tester - VAS 6551- by pressing On/Off button and calibrate it.
• Switch on ignition.
• Start engine.

• Take pressure reading on pressure tester - VAS 6551-.

Specification: min. – 0.30 bar

If the specified value is not reached, first check the delivery pressure in the fuel return system. Repair return system if necessary ⇒ Fuel supply system; Rep. gr. 20.

If the specified value is reached: Repeat test at injector ⇒ 4.3 Checking vacuum at high-pressure fuel pump (venturi nozzle)

If the specified value is still not reached: Replace high-pressure pump ⇒ 4.1 Assembly overview - high-pressure pump.