Can anyone please help me with an intermittent boost problem . The car is a MY93 Legacy Turbo but the engine is more or less identical to an early Impreza . It is fitted with an STI4 turbo & a gp N decat exhaust system but is otherwise standard . I had an intermittent lack of power so I fitted a boost gauge & discovered that when the power was bad I was only getting 0.5 bar max boost instead of 0.9 .

I took out the 3 port wastegate solenoid & tested it on a 12v supply & blew through it to make sure it wasn't blocked . I discovered that when there is no power going to the solenoid it allows the pressure from the turbo nipple to pass through to the wastegate but when it gets 12v it connects the wastegate to the air intake & allows it to close . I reassembled it all & in order to see if the solenoid was getting power I wired in a LED in parallel with the solenoid & put it inside the car . I know now that the reason for no boost is coz the waste gate is staying open . When the boost is bad the solenoid isn't getting any power coz the LED doesn't light up . Can anyone suggest what could be causing this intermittent power supply failure to the solenoid ? A mate who is a scooby mechanic suggested the throttle position sensor could be faulty - opinions .

Another thing I noticed when car is working normally the power wasn't going to the solenoid until I hit 3000 rpm . Then the boost builds up until it hits 0.9 bar & doesn't get any higher but the solenoid is still getting power at that stage so what's limiting my boost ? I thought that the wastegate should be closed well before 3000 rpm to allow the boost pressure to build up quickly & when the pressure reaches 0.9 bar it should be open again to limit the boost but my LED indicator is telling me otherwise .

I am considering fitting a Dawes device to cure this problem but I'm worried that I'll be covering up another problem like a faulty sensor .

Any suggestions greatly appreciated .

Derek

 

if it were me, id fit a dawse and remove the boost solenoid from the system, the dawse seams a much better method of control to me. you could be limiting boost for a number of reasons, onmy old turbo my boost would be limited sumtimes with a dawse fitted and no amount of twiddleing would sort it out, i never actualy figured out why it did this, but it died a death when it got to about 70k miles and hasnt did it scince with the replacement

 

BTT

 

How long have the following been fitted - STI4 turbo & a gp N decat exhaust system?
Has the problem arisen since fitting the turbo and exhaust system?

Cheers

 

The exhaust & turbo were already fitted when I bought the car last year . This problem has only started happening this past couple of months & has gotten worse this past 2 weeks .

It happened again today as I was going to work so at work I cleaned out all the valves & sensors near the solenoid , blew out every hose I could see , cleaned the maff sensor & its connections , cleaned the throttle pot connection , checked the ecu for faults ( none stored ) & did an ecu reset but the problem was still there . Then as I was driving home it cured itself . Confused - you bet !

Derek