Adjustment of Basic Boost Pressure

Adjustment of basic boost pressure

With the results of checking basic boost pressure on the road as a starting point, carry out adjustment as described below. The procedure described applies to all versions of the pushrod (straight or angled).

Tool: Adjusting pliers 13 94 066.

1 Jack up the car and slacken the end piece's locknut on the diaphragm unit, using tool 83 94 520.




2 Break the seal and remove the circlip, using tool 83 94 538. Unhook the pushrod from the flap valve's operating arm.

Important: When adjusting the end piece, grip it with the tool as close as possible to the threaded portion. This is to avoid the formation of burrs further along the pushrod which would cause the diaphragm unit's bearing to bind and so upset the system's boost pressure control.

For the correct basic boost pressure, see "Specifications"

3 Adjust basic boost pressure as follows:

- If basic boost pressure is too low, screw in the end piece (shortening the pushrod).

- if basic boost pressure is too high, unscrew the end piece (lengthening the pushrod).

- Turning the pushrod 1 complete revolution will change the basic boost pressure by about 0.03 bar.

Important:
The diaphragm unit must never be "prestressed" by less than 2 mm (2 turns), even if the basic boost pressure cannot be adjusted so that it lies within the set limits, see "Specifications".
If it is necessary to "prestress" the diaphragm unit by more than about 6 mm to obtain the correct basic boost pressure, the spring in the diaphragm unit is too weak or else there is a leak on the pressure side of the turbo system.

4 Connect the push rod to the operating arm and fit the retaining ring.

5 Continue with "Checking basic boost pressure on the road". Testing and Inspection

If basic boost pressure cannot be adjusted, continue with "Checking the flap valve and diaphragm unit". Testing and Inspection

6 Seal the push rod.

Important:
Cracks and other detects in the turbine casing which occur in the area close to the flap valve's mating surface can affect the boost pressure.
Unallowed crack running in the direction of the machined surface.
Cracks giving rise to a warped mating surface and causing gas leakage. Cracks in the turbine casing visible externally.
Turbine casing with warped inlet flange or severe disintegration of the machined contour surface.