Had a simular problem with my 91 RS - I almost got draged off by a late
model honda prelude.
In my case it occured after playing with the engine management computer, i
didn't attact one of the connectors to the computer properly. (silver- grey
box with yellow connectors located driver's side above right of the
accelerator peddel) so check this first. When my RS boosts above 5psi I
hear a denstintive relay 'click'. This controlles the wastegate (which
controlles the boost) From what i can remember the wastegate is actuated by
boost pressure, & in its 'unmanaged' state the wastegate will open at 5psi
The ECU prevents the waste gate opening by using a solenoid valve prevent
boost pressure getting to the waste gate (simular to a boost controller does
which you by from any car parts shop like Repco) The solenoids natrual state
is open so if it fails it doesn't result in overboosting -so check this.
swap it with a mates is the easest way. It is attached to a thick vaccuum
hose that runs from the manofild or just infront of the turbo to the valve
and then wastegate (or the other way aroud) and air intake resonator
Also check the relay switch mentioned above, sorry not sure where that is.
The turbo legacies (early naturally asperated legacys arn't) are also fitted
with a pressure sensor that could be the problem, but it is unlikely.
if you find that it is the solenoid valve and IF they are are expensive, you
might concider getting a boost controller instead (mentioned above), it will
do the same job for around NZ$90, and you can turn up the boost.
Caution: Don't boost your early legacys above 14psi, The formentioned
pressure sensor stops working somewhere between 14-15 psi, after that the
ECU ha no idea how much boost you are putting in and goes mad and sprays as
much fuel as it can, making for a rich mixture, and loss of power. Plus it
tends to f***K your engine.
Mike
Here is a unrecommended side note, as mentioned aboe the waste gate on the
(legacy) turbocharger will open at 5 psi, without ECU intervention and since
most cars (non-turbo) ECU fuel maps are programmed to operate upto 6psi of
pressure you could conceivably bolt on a small (automatic GT) turbo to any
legay/impressa/forester with only purchasing relativly non-expensive items.
