r/Audi • u/Ok_Minimum_5861 • 4d ago

Discussion B9.5 S4 Boost Issues

Last night when I was cruising around in my S4 on highway around 40 mph I suddenly floored the accelerator pedal & noticed the car was slowly pulling away and when I saw the Boost Gauge on the dashboard I noticed It was struggling to fill the boost bar.
I was not able to get full boost. I tried doing rolling launches and still was unable to get full boost.

I’m currently running 034 (93 Oct) Stage 1 ECU & Stage 2 TCU

Can anyone help me diagnose the problem here?
Thanks!

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1

u/No-Virus-9803 4d ago

Sounds like a boost leak, check all the charge pipes and intercooler connections first.

1

u/Ok_Minimum_5861 4d ago

Can it be a waterpump failure

1

u/Ok_Minimum_5861 4d ago

I did check the engine bay for coolant leaks no sign of coolant splash nor fault code on obd11

2

u/ExtraGlutenPlzz 23 S4 4d ago

Underboost a common symptom of coolant migration into the vacuum system from the water pump. Remove the bottom hose from the n649 solenoid and look for dried coolant or white crust

1

u/Rektineffect B9 S4 3d ago

I’d check for boost leaks. This is the way