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
740 Knock
Apr 07, 2004
1 Replies
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
Bryan vz wrote:
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