No particuller fault lads just a query on how it works. I understand the valve controls boost pressure 12 volt supply and a earthed duty cycled signal the tree pipes connected what are they delivering and how does this control boost.

They are delivering vacuum to the wastegate actuator or VNT mechnism.

It controls the boost by means of a closed loop system. The ECU gets a signal from the boost pressure sensor and opens the wastegate or alters the VNT mech depending on boost requirements.

Thanks Ross vacuum operated i understand to activate the wastegate the three pipes connected vac input, output to waste gate but the third is atmospheric pressure to the airfilter cant see why.

Sometimes it connects to the inlet side of the turbo depending on application.

I dont know off hand tbh.

just out of curiosity is the N75 valve the little thing that sits on the top of the intake pipe before the turbo and after the MAF?

Yes.

just out of curiosity is the N75 valve the little thing that sits on the top of the intake pipe before the turbo and after the MAF?

Isn't that the Diverter Valve? I always thought that the N75 was bolted to the bulkhead.

The N75 is next to the diverter near enough on the 1.8T, its on the bulkhead in the diesels.

The N75 is next to the diverter near enough on the 1.8T, its on the bulkhead in the diesels.

Correct me lads if im wrong turbo actuator for waste gate on petrol engines is opened by N75 using pressure from intake side of turbo.

Diesels use a vacuum to open waste gate from N75 when activated why is this.

On 1.8T the actuator is operated by PRESSURE from the inlet plenum via the N75 valve (don't know enough about diesel to be sure on that) . The N75 has 3 ports, one takes pressure from the plenum, one feeds pressure to the actuator, and the third effects a variable "leak" to atmosphere, the amount of bleed being dependent on the drive signal to the valve. This has the effect of decreasing the amount of pressure the actuator sees and hence how much it opens.

As the engine demands boost the valve will be open, to bleed air away from the actuator, holding the wastegate shut, as programmed boost level is reached the valve progressively shuts to reduce the bleed-off and apply more pressure to the actuator to open the wastegate and reduce the amount of exhaust gas going through the turbine. By controlling the N75 drive, the ECU can hence regulate boost pressure.