ADJUSTING
BASE BOOST
To check base
boost, drive the car until it reaches operating temperature (fans
cycle twice). Use as high octane gas as you will usually run. Don't
put in 103 octane just for the setting. Running lower than 91 won't
be good either. Disconnect the APC solenoid electrical connection.
Attach the pressure gauge and route it inside the car where you or an
assistant can read it while you drive. Connect it to a manifold
vacuum source. I use tees so that I can reconnect all the lines and
see the engine as the APC sees it.
Go for a drive, preferably so you can get as much boost as possible for as long as possible. On a manual, this is usually safest in third gear at about 2000 rpm starting point. A hill helps hold the load longer(so you don't rev up too quick to read the gauge). Hold the gas to the floor until you hit about 4500 rpm. Record the highest reading on the gauge. On an auto, try to push the car as hard as you can above 2750 rpm without hitting the kick down.
NON APC TURBOS
On non APC turbos, the adjustment you do will set the max boost. You have no APC solenoid to unplug, just attach the gauge and drive.
On 78-80 Turbos, you have to disassemble the diaphragm housing and turn the nut on top of the spring seat. One half turn in increases the boost by about 1 psi. The spec is 7-8 psi.
On 81-82 1/2 Adjust boost by turning the wastegate rod. Shortening the rod increases boost. The spec is 8-9 psi. One turn of the rod changes the boost by about .6 psi Make sure you loosen the rod lockout, and then remove the rod from the turbo arm to turn it. Turning the threaded part of the rod will turn the diaphragm and can tear it, rendering it useless. Full boost with no control will result, the overboost switch kicking in very early with acceleration.
82 1/2-> APC TURBOS
Since different year models have different part number ECUs, they are designed to handle different levels of boost. This is a compilation of the specs. The specs given are the high end. See the above note on adjusting the wastegate rod. This makes 9000s a bit of a challenge to adjust without getting burnt. If you get the clips off, its not too bad.
82 1/2 -> 84 4.85 psi
85 -> except SPG 5.5 psi
SPG except 90 5.9 psi
90 SPG 6.3 psi
DI/APC 6.0 psi
NOTE: adjusting the base boost on DI/APC cars requires max boost recalibration. Set base boost as outlined above by unplugging the solenoid and driving with a gauge attached. Boost is adjusted by the wastegate rod. Then the system must be readapted for max boost. With the APC solenoid reconnected, jump pins 1 and 2 of the throttle switch together and drive as if testing base boost. This may take several attempts before the ECU resets the max boost it allows. The car will die at idle with the pins jumped, so you have to work the gas to keep it running. Pick your recalibrating route so you can undo the jumper after it takes. You will see it go well into the red and then come back. When it readapts, the distance into the red will not exceed the dotted yellow lines by very much at all. Most of the time, this works fine, but I caution that sometimes, ISAT is required to clear the ECU and get it to readapt. This is rare, but does occur.
TRIONIC 6.0 psi
Trionic requires a test drive to recalibrate max boost as setting base boost except with the Boost Solenoid connected. It does not require the jumper wire.
TCS cars require ISAT commands to recalibrate. I would not attempt resetting them without ISAT.