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Hello Steve:
Like you say, the scope test for wave forms may be most the most conclusive. But then one needs a scope. I ran the cheap and easy LED test I recently posted. This test indicated no problem with the knock sensor on the 760T, but still I thought the car did not run at its best. I had also tested for resistance and found a bit over 300K ohms rather than the prescribed 4.8-5.2M ohms. So I put in a knock sensor with a resistance of 4.9M ohms. The car runs much better with this knock sensor. I still have to try the voltage test recommended by JohnB. As for his other suggestion to disconnect the knock sensor and see how the engine runs, I did this. I found the engine ran much worse, indeed the car had practically no acceleration from rest with the old sensor disconnected. Still, this knock sensor (300K ohms) proved to be operating marginally at best once I put in another (4.9M ohms). So far, the LED test revealed a disconnected or completely shot knock sensor, but not one that operates marginally. Likewise, the disconnect test. Resistance seems to offer at least a good clue when trying a used knock sensor. The scope test may be conclusive, but it requires a scope. Finally, I ordered a new (probably upgraded) Bosch knock sensor from Nick Bauer at www.fcpgroton.com for $40. Best regards.
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