Problem job: defective crankcase ventilation causes loss of power

Ventilation is essential to remove blow-by gases that form in the cylinder during combustion from the crankcase

Problem job: defective crankcase ventilation causes loss of power
Installation position of the PCV valve on the cylinder head.

In vehicles with turbochargers, power loss, rough idling, or whistling noises are indicators of a defective crankcase ventilation system, MAHLE Aftermarket reports.

Pressure control valves, known as positive crankcase ventilation (PCV valves), have been installed for crankcase ventilation on VW Group’s 1.8 and 2.0 TFSI engines.

MAHLE Aftermarket say that because of the installation position of the PCV valve, it is easily overlooked during troubleshooting.

When replacing the turbocharger, the engine periphery must therefore always be checked thoroughly and the engine control unit’s fault memory read.

The PCV valve ensures the crankcase is properly ventilated in different load cases.

Idling or overrunning

The blow-by gases are supplied downstream of the throttle flap and thus also downstream of the turbocharger, as in this load case there is negative pressure in the inlet manifold.

Partial or full load

The blow-by gases are supplied upstream of the turbocharger, as in this load case there is overpressure in the inlet manifold.

In the second case (under partial/full load), the boost pressure presses on a diaphragm, which causes the PCV valve to supply the blow-by gases accordingly.

If there is a defect, for example a crack in the diaphragm, the boost pressure may escape directly into the crankcase and the above faulty symptoms occur.

For further information about MAHLE Aftermarket, click ‘more details’ below.

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