pnebbs

I apologise for this not being about an Impreza but I drive a 94 Legacy GT-B, this is the model with the twin sequential turbos, this normally boosts to around 11-12psi.

Over the last couple of weeks I have experimenting with a bleed valve to see if I could increase the boost slightly (I used the bleed valve with amazing success with my last car, An 89 Supra Turbo). Putting the valve in line with either wastegate makes absolutely no difference to the boost levels.

Even disconnecting the vacuum line from the wastegate completely makes no difference (I have not tried disconnecting both wastegate at the same time though.

2 nights ago I removed the bleed valve from the first turbo and put it back to standard and since then the car will only boost to 7psi, even with the line disconnected from the second turbo.

Has anybody any idea

a) Why I can now only get 7psi

b) Why I can't increase the boost (In the past, Supra, Ur-Quattro, 323 Turbo the usual problem with a wastegate is not increasing the boost too much)

Paul

Dr Hu

My only suggestion is, put everything back as it was, and try an ECU reset - leave the battery off for a couple of hours, then try again, its just possible that the ECU sensed a shut wastegate and lowered the boost delivered accordingly by opening the duty solenoid. Clearing the ECU memory should get around this.

Other than that make sure both wastegates are moving against their springs freely (i.e not stuck slightly open) and all the other hoses and stuff are secure.

All I can suggest - sorry.

MorayMackenzie

As I understand it, the turbocharger control system is setup so that the turbo will boost up to 7psi and stop there UNLESS the ecu controlled wastegate solenoid bleeds from the actuator control hose.

Check (or get an expert to check) all the vaccuum lines are back in the correct place. ECU reset might not be a good idea if you have any blocked or swapped control lines. It may be an idea to get an expert to plug in a Select Monitor and check the ecu's state of mind.

It could be that the ecu has decided to run in a get-you-home mode because the turbo control system isn't working correctly.

Check your wastegate control solenoid/s(?) are working.

Good luck,

Moray

pnebbs

The plumbing on the sequential turbos is horrendously comlicated (Why didn't Subaru just use the STi engine), there are over 25 vacuum pipes and at least 6 solenoid valves controlling boost and what turbo does what and when - I don't think UK Subaru garages would have any idea (plus they refuse to look at it anyway)

I wonder if the wastegates are connected because it is very obvious when the two different turbos are operating and they are both now boosting to 7psi even if one wastegate is completely disconnected from the boost pressure

Paul (Confused)
I'm trying to map the sensors, connectors, exhaust pipes etc, you'll be amazed how complicated the system is and how Subaru still managed to get a hole in the boost between the turbos