2. Checking Pressure Accumulator And Pressure Control Valve

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This test allows you to analyze whether the pressure accumulator or the pressure control valve is not working properly.
The analysis is difficult if neither component is working properly. In this case, the pressure accumulator and the pressure control valve (the complete hydraulic pump with pressure control valve and reservoir) must be replaced anyway.
The test involves counting the number of clutch pedal actuations (with the pressure accumulator full) until an increase in pedal pressure is clearly felt (pressure accumulator is empty).
In some cases, you may also have to measure the change in fluid level (fluid volume) in the reservoir (between full and empty pressure accumulator).
Ensuring that the pressure accumulator is full (for the test) means: Cold-start the engine and leave it running at 2000 rpm for approx. 20 seconds. Then stop the engine.

Cold-start the engine (accumulator temperature of approx. 20 °C) and leave it running at 2000 rpm for approx. 20 seconds (pressure accumulator is full).
With the engine switched off, press the clutch pedal repeatedly until an increase in pedal pressure can be clearly felt (pressure accumulator is empty). While doing this, determine (count) the number of times the clutch pedal must be pressed to achieve an increase in pedal pressure.

If the system is intact, up to 20 actuations are possible before an increase in pedal pressure can be clearly felt.

In the event of other signs and symptoms, use the following overview to check whether the pressure accumulator or the pressure control valve is not working properly .

If the previous test is not sufficient for analysis purposes, you may also have to measure the change in fluid volume in the reservoir (Step 2).

Replace the pressure accumulator if:

Fig 1: Locating Pressure Accumulator
Courtesy of PORSCHE CARS NORTH AMERICA, INC.
- More than 30 actuations are possible before an increase in pedal pressure can be clearly felt.
- The fluid volume in the reservoir (in the engine compartment), between full and empty pressure accumulator, has changed by more than 200 cm³ .
- Only one or two actuations are possible before an increase in pedal pressure can be clearly felt.
  The pressure control valve is defective (replace complete hydraulic pump with pressure control valve and reservoir) if:
  
  Fig 2: Identifying Pressure Control Valve Components
  Courtesy of PORSCHE CARS NORTH AMERICA, INC.
- Only a maximum of eight actuations with power assistance are possible (before an increase in pedal pressure can be clearly felt) and the change in fluid volume in the reservoir, between full and empty pressure accumulator, is less than 60 cm³ .
- When you press the clutch pedal, with the engine running, there is an increase in pedal pressure and/or the pedal feels different.
If the previous test is not sufficient (for analyzing which component is defective), repeat the test procedure and also measure the change in fluid level in the reservoir (in the engine compartment).
One of the manual metering pumps WE 1372 (which is used exclusively for Pentosin) can be used as the suction pump and measuring device (for the fluid volume).

Alternatively, a suitable suction pump and an appropriate measuring vessel can also be used.
1. 2.1. Cold-start the engine (accumulator temperature of approx. 20 °C) and leave it running at 2000 rpm for approx. 20 seconds (pressure accumulator is full).
  Measure the fluid level in the Pentosin reservoir in the engine compartment when the engine is stopped (record the current fluid level value).
2. 2.2. Press the clutch pedal repeatedly until an increase in pedal pressure can be clearly felt (pressure accumulator is empty). While doing this, determine (count) the number of times the clutch pedal must be pressed to achieve an increase in pedal pressure.
3. 2.3. Then continue to drain Pentosin until the fluid level in the reservoir is the same as it was before you pressed the clutch pedal. The amount of Pentosin removed (the fluid level) is another differentiating factor that will help to determine which component is defective (pressure accumulator or pressure control valve).
  Based on the amount of Pentosin removed, replace either the pressure accumulator (if the change in volume is more than 200 cm³ ) or the complete hydraulic pump with pressure control valve and reservoir (if the change in volume is less than 60 cm³ ).