740 Knock

Discussion in 'Volvo 740' started by Bryan vz, Apr 7, 2004.

  1. Bryan vz

    Bryan vz Guest

    My 1990 740T with 250K mi has a rough idle that smooths out at 1500 rpm (in
    "park" in the driveway). When under load (whenever it's in gear) it has a
    BAD knock that renders it undrivable. Any experience with this?

    Bryan vz
    Kentucky USA
     
    Bryan vz, Apr 7, 2004
    #1
  2. Bryan vz

    Half a Bee Guest

    Using good fuel, right ? OK, so maybe it's the knock sensor gone kaput.
    The car periodically tests just how efficient it can be by
    advancing the spark timing.

    How you car thinks:
    Can I detect knock ? No ? OK, then advance the timing.
    Can I detect knock ? Yes? OK, retard timing.

    If the sensors are not working (or some part of the advance mechanism is
    stuck) then knocking is guaranteed. Smooth no-load operation at 1500
    rpm is just a symptom of the flywheel rotating fast enough that you
    don't notice the knock.

    Time to visit your friendly Volvo dealer.

    Chris
     
    Half a Bee, Apr 13, 2004
    #2
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