If you do not have a pressure signal to the wastegate, you will likely overboost the snot out of the car. Look at the picture again. The spring only works as advertised with a manifold pressure signal (the one you had disconnected). The manifold pressure signal, working in conjunction with exhaust backpressure, will move the wastgate flapper door against the spring force and open the gate. The whole premise of the N75 valve is that it can *delay* or *bleed* the pressure signal to give you higher boost than base spring pressure. The safety feature is that with the pressure signal hooked up, the N75 can allow the entire signal to go to the gate and open it earlier instead of pulsing the valve to control boost to some higher value than base spring pressure. This is done in the event that the ECU sees something it doesn't like (knock, high IATs, etc)

In short, losing the pressure signal to your wastegates and going WOT is about the worst thing you can do to the motor.

You need to quickly get in writing that the shop left this hose disconnected and test drove the car.

 

+1, no WG hooked to N75 = full on boost and then engine can go boom. The N75 holds the pressure back to keep the WG from opening, but if no pressure getting to the WGs, then they will never open.

 

My Impreza has an overboost cutout which kills the ignition if the boost goes too high,it happens sometimes when the wastegate solenoid gets dirty. Normal boost is 0.9 bar and the cut is at 1.2

Does the 996t have similar protection? I hope so

 

I beleive it can snap the TB shut in a worst case scenario, however some tuners remove this. The issue is that the pressure tranducer has to sense the overboost, report it to the DME, DME decided its a bad thing, DME sends a signal to the TB and the TB has to physically move shut -all of this takes time (yes were talking milliseconds but at high rpm there are a lot of combustion events happening in those ms) and the engine may or may not survive.

 

What about the ECU boost cut off at 1.3 bar as a factory safeguard? If 1.3 bar boost was reached, it would throw the car into limp mode. Unless it was upgraded via tuning that would allow more than 1.3 bar. Or was the ECU not able to get the boost reading due the hose being dicconnected?

Richard, did the car go into limp mode?

 

I'd pull the pan to check if any metal from the turbo made it to your oil.

 

The car if I recall correctly has a AMS tune and turbos.. thus the 1.3 boost cut if probably out of the way... Like it should...
IM guessing those who ran it had no idea but should have been known better...
Markski

 

Marski is correct I have an EPL tune with K16 AMS billet Turbos (or had), its amazing that such a little pipe like the N75 contoller has such a key roll, its just unfortunate for all concerned and I guess its going to cost 10K at the very minimum.

 

It is very unfortunate. Most US shops carry insurance for "shop accidents" that cover this sort of thing. Maybe yours does too?

Best of luck with the repairs.

Jon

 

My bad, I looked the pic after few GT's..

 

I guess the simple way to resolve this is to get the ECU read by somebody independent, if it went to 1.8 BAR boost for example without the N75 connected would in all cases an ECU readout show exactly this when and where or does it read as overboost without the exact BAR measurement and when it happened ?

 

I'd be picking the car up yesterday and taking somewhere else.

 

Yes it is going somewhere else for the work for sure but before I take back possession of a car with a damaged engine which I delivered in perfect working order I need to set some ground rules, comments about what the ECU readout will tell me please ?

 

My point is that it shouldn't have such a key role, there should be something there to back it up and save the day if it fails.

From reading posts above someone mentioned a cut at 1.3, does a standard car have this I can't tell from reading the posts? it also seems that tuners remove it which if true is unbelievably irresponsible.

So is it true to say that tuners modify cars to run higher boost and then turn off the protection.

I personally would not modify my car unless I knew there was protection.

I work in the chemical industry and if you wanted a system to work at a higher pressure you normally have to put extra protection systems in place after doing extensive risk assesments to maintain the same level of safety, you would never turn them off.

 

yes I agree but it looks likes this is not the case here and the N75 plays an extra critical role, can we focus on what the likely ECU readout will say