knock sensor test. 1989 v.w golf gti 1.8 8valve?

i suspect the knock sensor is u/s. testing with an ohm meter
shows open cct across all 3 terminals. do you have any
typical values? i have tried slackening and retightening to
correct torque with no effect. my problem is the ignition
timing is way too advanced, no work has been done on the
car, the distributor has not moved and all other parts seem
to give correct values compared to haynes manual. car runs ok
but pinks under load badly. using LRP 97 RON fuel.