Audi TT Turbocharging and Forced Induction Systems 3

Question 1

On the Audi TT Mk1 1.8T engine, what turbocharger model is factory installed in the 225 hp variant?

Accepted Answer

K04 turbocharger

Answer

K03 turbocharger

Answer

KKK K14 turbocharger

Answer

Garrett GT2871R

Question 2

What is 'boost creep' and what component failure commonly causes it on the Audi TT?

Accepted Answer

Uncontrolled boost rise beyond target caused by a stuck or undersized wastegate

Answer

Boost dropping at high RPM caused by a failed MAF sensor

Answer

Turbo overspin caused by a missing oil return line

Answer

Boost pressure spike at idle caused by a leaking diverter valve

Question 3

On the Audi TT, which cooling system supports the water-to-air intercooler loop independently of the main engine cooling circuit?

Accepted Answer

A separate low-temperature auxiliary coolant circuit with its own electric pump

Answer

The engine's thermostat-controlled primary circuit

Answer

The HVAC cabin heater core loop

Answer

A passive thermosiphon circuit requiring no pump

Question 4

What is the consequence of running an Audi TT turbo engine with restricted or coked oil return lines?

Accepted Answer

Oil backup into the turbo center housing causing seal failure and oil consumption

Answer

Lean fuel mixture due to crankcase pressure affecting MAF readings

Answer

Boost pressure drop from increased backpressure

Answer

Overheating of the intercooler coolant circuit

Question 5

When inspecting an Audi TT turbocharger for shaft play, what is the acceptable axial (in/out) play specification?

Accepted Answer

Up to 0.05 mm is acceptable; greater indicates bearing wear

Answer

0.0 mm — zero play is required

Answer

Up to 0.5–1.0 mm axial play is within specification

Answer

Axial play is not measurable; only radial play is checked

Question 6

What role does the Boost Pressure Control Solenoid Valve (N75) play in the Audi TT turbo system?

Accepted Answer

It modulates vacuum signal to the wastegate actuator to control boost pressure

Answer

It opens the blow-off valve to vent compressor pressure

Answer

It regulates fuel pressure in relation to boost

Answer

It switches the low-temp intercooler pump on and off

Question 7

What intake noise or symptom is commonly heard when the diverter valve fails open (stuck in bypass position) on the Audi TT?

Accepted Answer

A loud hissing or whooshing sound under boost with significant power loss

Answer

Backfiring through the exhaust on deceleration

Answer

A rattling noise from the turbo impeller

Answer

Whistling from the wastegate actuator rod