Audi TT Turbocharging and Forced Induction Systems 1 — Questions and Answers
Question 1: What type of turbocharger is used on the Audi TT 2.0 TFSI engine?
- Twin-scroll turbocharger (Correct answer)
- Variable geometry turbocharger (VGT)
- Centrifugal supercharger
- Roots-type supercharger
Correct answer: Twin-scroll turbocharger
The 2.0 TFSI uses a twin-scroll turbocharger that separates exhaust pulses from cylinder pairs to improve spool response and reduce turbo lag.
Question 2: What is the typical boost pressure range for a stock Audi TT 2.0 TFSI (Mk2)?
- 5–8 psi (0.34–0.55 bar)
- 10–15 psi (0.69–1.03 bar) (Correct answer)
- 16–20 psi (1.10–1.38 bar)
- 22–26 psi (1.52–1.79 bar)
Correct answer: 10–15 psi (0.69–1.03 bar)
The stock Mk2 TT 2.0 TFSI operates at approximately 10–15 psi of boost under normal driving conditions.
Question 3: Which component is responsible for regulating boost pressure by venting excess exhaust energy on the Audi TT turbo system?
- Blow-off valve (BOV)
- Wastegate (Correct answer)
- Intercooler bypass valve
- Boost controller solenoid
Correct answer: Wastegate
The wastegate diverts exhaust gases away from the turbine wheel to limit and regulate maximum boost pressure.
Question 4: What is the purpose of the diverter valve (DV) found on the Audi TT's turbo system?
- It redirects boost pressure to the wastegate
- It recirculates compressed air back to the turbo inlet when the throttle closes (Correct answer)
- It opens to cool the intercooler under boost
- It increases exhaust backpressure at idle
Correct answer: It recirculates compressed air back to the turbo inlet when the throttle closes
The diverter valve (also called a recirculating bypass valve) vents pressurized intake air back upstream when the throttle closes, preventing compressor surge.
Question 5: On the Audi TT, the N249 valve is associated with which function?
- EGR flow control
- Turbo boost pressure recirculation bypass (Correct answer)
- Fuel pressure regulation
- Secondary air injection switching
Correct answer: Turbo boost pressure recirculation bypass
The N249 is a solenoid valve that controls the diverter valve, helping manage boost pressure recirculation to prevent surge.
Question 6: What symptom is most commonly associated with a failed or leaking diverter valve on the Audi TT?
- Excessive oil consumption
- Loss of boost pressure and hesitation under acceleration (Correct answer)
- Rough idle and misfires at low RPM
- Overheating coolant temperature
Correct answer: Loss of boost pressure and hesitation under acceleration
A failed DV leaks boost pressure, causing reduced power and noticeable hesitation when the driver accelerates after a brief throttle lift.
Question 7: Where is the charge air cooler (intercooler) located on the Mk2 Audi TT 2.0 TFSI?
- Front-mount, behind the bumper grille
- Top-mount, above the engine
- Side-mount, in the front fender well
- Internal water-to-air, within the intake manifold (Correct answer)
Correct answer: Internal water-to-air, within the intake manifold
The Mk2 TT 2.0 TFSI uses a water-cooled indirect intercooler integrated into the intake manifold, circulated by a separate coolant loop.
Audi TT Turbocharging and Forced Induction Systems 1
What type of turbocharger is used on the Audi TT 2.0 TFSI engine?