Not unless you have a 25psi spring?

You have a mechanical issue.

No. When disconnected electrically, the N75 should send all boost to the wg line, which should cause boost to bleed off when the pressure overcomes spring tension.

The N75 DOES NOT BLEED OFF BOOST AS YOU SUGGESTED IN YOUR POST.

I can't stress this enough. It bleeds off boost AWAY from the wastegate, which is a very different thing.

If you are still seeing boost, either the N75 is broken (it is incorrectly bleeding off boost from the wastegate line) or you have torn wastegate lines.

Pressure test your wastegate lines.

Alternately, you can crimp off the hose from the bleed leg (longest leg) of the N75 and retest.



The one you want is the leg pointing to the left above.

Peak boost occurs around 4k rpm, both WOT (N75 in the 90%) and part throttle (N75 is always at zero %).
Both tapering down at higher rpm.
Under WOT, max boost is 16 psi , while part throttle going to 25 psi.
With N75 electrical connector pulled off, both WOT and part throttle go 25 psi (possibly higher; didn't dare).

If mechanical issue, what mechanical issue could cause the different behavior of the N75/ECU (throttle position dependent) and boost?

You have a sticking wastegate, problems with the lines or similar.
Put the ECU away and fix your car.

If WGDC is 0 and your boost is doing all sorts of crazy stuff it's a purely mechanical issue. Nothing to do with electronics.

Personally I think your N75 is hooked up wrong.
You have the long port (bleed off) going to the wastegate and the short port going to the bleed off.
So it's doing the reverse.

That's why when the ECU wants to request boost it reduces it and when it wants to reduce boost it requests it.
You ought to look over other schoolboy errors as well and pressure test the car before going into the ECU

Very much looks like it. Friend brought the car in for timing belt and radiator work; he only mentioned some suddeness during part throttle.
Furthermore, previous owner told him the car has "Giac PC16 X" (does not exist) and 330 injectors. Car has DV relocation.

I take the front off today and go through the connectings (needs new fan blade anyways). While accessible, will move the WG actuator, and measure the N75.

i will report back afterwards.

"long leg" of N75 was connected to actuator, short leg to TIP!

Thanks for all the help.

Will put together tomorrow, but may be end of the week by the time i can take her out for test drive and log run (car is on stands again for more work).

Yes, you were right on the money. Only surprised that under WOT, the boost was 'only' 16 psi, and weird pressure (for Giac PC16 anyways) of 25 psi only occurred during partial throttle. Any explanation for that?