Checking the boost pressure (VW Passat B4)

A necessary condition for the efficient operation of the turbocharger and obtaining the required boost pressure is complete tightness of the connections both on the intake manifold side and on the exhaust manifold side. The boost pressure is checked at full engine load while driving or on a stand with running drums. The check at each pressure measurement should be carried out for 10 s, for which disconnect the vacuum hose from the intake manifold, going to the fuel supply corrector for the boost pressure of the high-pressure fuel pump. Connect the hose of the control pressure gauge through a tee to the intake manifold and vacuum hose. Move the pressure gauge into the car interior, while it can be placed on the right front seat or on the dashboard near the windshield, making sure that the pressure gauge hose is not pinched when closing the hood.

Open the shut-off valve of the pressure gauge by pressing in the direction of the pressure gauge. Measure the boost pressure at full engine load:

• on the stand: in 3rd gear at a crankshaft speed of 4000 rpm:
• while the vehicle is moving: in 2nd gear, while simultaneously braking the vehicle to maintain a speed of approximately 60 km/h.

Increased boost pressure indicates a faulty wastegate valve. In this case, the turbocharger must be replaced. If the boost pressure is low, disconnect the pressure relief valve hose from the air intake hose, close the hose opening with a suitable 25 mm diameter plug and secure the plug with a hose clamp. Repeat the boost pressure test. If the boost pressure is normal, replace the pressure relief valve. If the boost pressure remains low, replace the turbocharger.

(The information is available on the website vwmanual)