Adjusting the basic boost pressure on the Saab 9000


The APC system used on all full-pressure Saab 9000 Turbos (although implemented in at least three different ways over the years) controls the turbo boost pressure above a certain level known as basic boost (or base boost). This level of boost is set mechanically by the wastegate actuator on the turbo and should be set to a prarticular pressure, depending on the model. This procedure shows how to measure and adjust the base boost pressure.

Time required

Each adjustment requires only a few minutes. However, if further adjustment is required, the engine must be allowed to cool sufficiently to touch. From my experience, this typically takes a few hours.

Tools required

N.B. These were the tools I found necessary for the TD04 on my manual '96 Aero. Other turbo installations may require different tools.

  • 10mm or 11mm, depending on model
  • Boost gauge
    A boost gauge is essential for measuring the base boost level. There is no other way. The more accurate (and precise) the better, but I get good enough results from a gauge that is not very precise (I reckon I can resolve to within 0.05 bar on this gauge, with care - this is just barely enough precision for this task). A gauge with a range of around 0.7 bar (10PSI) will provide best resolution for this task. This is what I use.
    I also have a TIM boost pressure gauge, made in the UK, which has a range of 2 bar. While this is not very precise due to the small scale and large range, I have used it to measure base boost. It is better suited to measurement of peak boost. This gauge is designed to be mounted inside the car, but I only use it for adjustment so I don't have it permanently mounted.


The various parts mentioned in this procedure are shown below (Aero with Mitsubishi TD04 turbo shown):

If the basic boost pressure has been lost completely

If the basic boost pressure adjustment has been completely lost, for example the wastegate actuator or turbocharger has been dismantled or replaced, an initial setting may be set as follows:

  1. If necessary, jack up the front of the car and support it on axle stands.
  2. Slacken the locknut on the wastegate actuator rod.
  3. Remove the circlip or spring clip retaining the rod end on the wastegate lever and unhook the rod end from the pivot on the lever.
  4. Unscrew the rod end until the hole in the rod end just slips over the pivot, with the wastegate held in the closed position.
  5. Screw the rod end back in by 3.5 turns. This will pre-stress the actuator by approximately 3mm when the wastegate is closed.
  6. Refit the rod to the wastegate and refit the retaining clip.
  7. Measure the basic boost pressure as described below and adjust if necessary.

Measuring the basic boost pressure

  1. Connect a boost gauge to the car. My '96 Aero has a vacuum takeoff point for just this purpose situated on the inlet manifold. It is normally blocked off by the rubber plug seen in the foreground. Other models may require the insertion of a tee-piece (supplied with the TIM gauge) in one of the vacuum lines. Do not connect to the PCV hose (on top of the cam cover with a white plastic valve halfway along it).

  2. On non-Trionic cars:

    1. On non-Trionic cars, disconnect the electrical connector on the APC solenoid valve. This is mounted on top of the radiator on the left side of the car (battery side). It has an electrical connector and three rubber hoses connected to it. Don't disconnect the hoses.
      (I don't have a photo of the non-Trionic style of valve. If anyone can supply a photo showing the valve and its location, I will be very grateful).

    2. Take the car for a test drive and with the engine at normal operating temperature, do some hard accelerating. A steep hill can help here.
      Note the maximum boost pressure indicated on the gauge.

  3. On Trionic cars and LPT models:

    1. Take the car for a test drive and with the engine at normal operating temperature, select third gear (manual or automatic) and accelerate at full throttle from below 1500 RPM (avoid the kickdown on models with automatic transmission). As the engine speed approaches 3000 RPM, press the brake while holding the accelerator, to achieve full load at 3000 RPM (pressing the brake pedal also causes Trionic to drop the boost pressure to base boost on non-LPT models). Note the pressure on the gauge.

  4. If the basic boost pressure is not within the specification, adjust it as described below and repeat the measurement.

Adjusting the basic boost pressure

N.B. Perform this operation with the engine cold. Even a few seconds of running can make the turbocharger too hot to touch.
It is best to do this while parked on a hard, even surface (e.g. concrete or asphalt, not grass) to minimise the risk of losing the retaining clip should it spring free suddenly.

  1. If necessary, jack up the front of the car and support it on axle stands.

  2. Holding the wastegate actuator rod near the threaded end with a pair of pliers, slacken the locknut using a 10mm or 11mm spanner. It is important not to hold the rod near the wastegate actuator (the round can) as any slight damage to the rod in that area can cause the rod to bind in the actuator.

  3. Remove the circlip or "R" clip retaining the rod end on the wastegate lever pivot.

  4. Screw the end piece in (shorten the rod) to increase boost pressure or out (lengthen the rod) to reduce it. See the specification for the approximate relationship between number of turns and pressure adjustment. Best performance will be achieved by adjusting towards the upper end of the specification. However, exceeding the specification can cause problems, including the risk of engine damage in adverse conditions.

  5. Replace the rod end on the wastegate pivot and refit the retaining clip. Note that on my Aero, the hole in the pivot for the "R" clip is vertical and it would be much easier to insert the clip from underneath than from above. However, it would then also be much easier for the clip to fall out. I have become practised at inserting the clip from above.

  6. Once again holding the rod with a pair of pliers near the threaded end, tighten the locknut.

  7. Measure the basic boost pressure using the method described above. If necessary, allow the engine to cool and repeat the adjustment.

Basic boost specification for various 9000s

Note: all specifications were originally specified in bar and the conversion to PSI is approximate.

These are the specifications I have been able to find so far. If your car is not listed here and you know what the basic boost pressure should be, I would be happy to hear from you. I'm especially curious about the specification for the rarer, higher-powered 9000s such as the CS Turbo S and the Carlssons.

Basic boost pressure
Approx. adjustment per full turn
PSI (approx.)
2.3 Turbo (except manual Aero)
0.37 - 0.43
5.5 - 6.5
Aero (manual)
0.42 - 0.48
6.0 - 7.0
2.3 light-pressure turbo
0.37 - 0.43
5.5 - 6.5
2.0 light-pressure turbo ('92-'93)
2.0 light-pressure turbo with intercooler ('96-on)
0.37 - 0.43
5.5 - 6.5
2.0 Turbo (non-Trionic)
0.34 - 0.37
5.0 - 5.5