VW Fuel Systems & Injection Technology 3

Question 1

A VW TDI engine starts fine but loses power at high RPM. Fuel rail pressure drops below spec under load. What is the MOST likely cause?

Accepted Answer

Worn or failing high-pressure fuel pump

Answer

Faulty coolant temperature sensor

Answer

Stuck open EGR valve

Answer

Defective mass airflow sensor

Question 2

What is the function of the fuel metering unit (FMU) on a VW TDI high-pressure pump?

Accepted Answer

It controls how much fuel enters the HPFP to regulate rail pressure

Answer

It measures the quantity of injected fuel per cycle

Answer

It cools the high-pressure pump with return fuel

Answer

It prevents fuel from returning to the tank

Question 3

In a VW TSI engine, a worn high-pressure fuel pump cam follower can lead to which serious failure?

Accepted Answer

Low rail pressure and potential camshaft lobe damage

Answer

Evaporative emission leaks

Answer

Turbocharger compressor wheel damage

Answer

Throttle body carbon buildup

Question 4

When replacing fuel injectors on a VW common rail TDI, what coding procedure must be performed in the ECU?

Accepted Answer

Enter the new injector IQA correction codes via VCDS

Answer

Throttle body adaptation

Answer

Reset the transmission adaptation

Answer

Perform a camshaft position sensor reset

Question 5

What is the purpose of the fuel return restriction orifice found in some VW TDI injector return lines?

Accepted Answer

To maintain a minimum backpressure on the injector return to ensure proper needle seating

Answer

To increase fuel pressure at the injector

Answer

To prevent fuel from flowing backward into the rail

Answer

To reduce fuel temperature in the return line

Question 6

A VW FSI engine exhibits rough idle and long-term fuel trim (LTFT) values that are significantly positive. What should the technician check first?

Accepted Answer

Fuel rail pressure at idle to verify adequate high-pressure delivery

Answer

Evaporative purge valve for leakage

Answer

Oxygen sensor heater circuit

Answer

Throttle position sensor calibration

Question 7

Which VW fuel system component is responsible for maintaining residual pressure in the fuel rail after the engine is switched off to aid hot restarts?

Accepted Answer

High-pressure fuel pump check valve

Answer

Fuel pressure regulator bleed valve

Answer

Fuel injector return check ball

Answer

In-tank pump pressure relief valve