Question about 1992 Saab 900

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APC Solenoid Valve Knocking

APC Solenoid Valve is making this repeated knocking sound. Its from a 1988 Saab 900 Turbo 16V, it sounds like its opening and closing really fast. and when I unplug the wire it stop. What could this be?

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The APC valve regulates boost pressure (via the wastegate) to avoid over-pressurising the engine. It ensures that a safe boost pressure isn't exceeded. Don't run with it disconnected or you risk blowing the engine!

Problem areas can include: knock sensor on the engine block (also poor quality fuel, dirty engine causing knock); engine ECU.

You need to provide more information about when this happens:

hard accelerating? (likely poor quality fuel, dirty plugs/engine causing knock) and general driving similar.

idling? possibly a knock sensor or ECU related problem

What rpm? what boost gauge pressure?

as an outside chance, maybe a sticky wastegate

Saabreur

Posted on May 30, 2009

  • saabreur
    saabreur May 30, 2009

    The APC valve regulates boost pressure (via the wastegate) to avoid
    over-pressurising the engine. It ensures that a safe boost pressure
    isn't exceeded. Don't run with it disconnected or you risk blowing the
    engine!

    Problem areas can include: knock sensor on the engine block (also poor quality fuel, dirty engine causing knock); engine ECU, and boost pressure sensor on the intake manifold after thethrottle body.

    You need to provide more information about when this happens:

    hard accelerating? (likely poor quality fuel, dirty plugs/engine causing knock) and general driving similar.

    idling? possibly a knock sensor or ECU related problem

    What rpm? what boost gauge pressure?

    as an outside chance, maybe a sticky wastegate

    Saabreur

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