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valve slap triggering knock sensor? 700 1985

posted by  Rtilghman on  Wed Jan 9 09:58 CST 2002
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brickers:

A little while back I had a discussion on this board with someone regarding a problem with my 1985 745t's acceleration. Basically, acceleration seems greatly retarded when I first begin to accelerate, but the car takes off once I reach 2700rpms or so on the tach. Someone mentioned that the knock sensor will retard engine timing up to 13 degrees if knock is detected, and that the knock sensor is deactivated around 2700rpms. Since I've replaced most of the fuel delivery system and cleaned the injectors, it would seem that the knock sensor is the likely culprit.

The problem is that I don't believe my engine has any knocking (have yet to put a stethoscope or hose to the thing, but I can't hear any outright). However, I have 204k on the engine, and there is noticeable piston slap. Could valve slap trigger the knock sensor to retard the engine?

I have also heard that, over time, the knock sensor/knock sensor bolt can become slightly loose in the grooves, allowing it to detect false knock and unnecessarily retard the engine. Could the two be working together to retard my engine sub-2700rpms?

What solutions might I apply to my problem? I can live with the acceleration loss (I'm not looking to burn the wheels on a 17 year old car), but if it's possible to fix it I figure I might as well try. Is there something I can spray on the knock sensor bolt to firm it up in the grooves a little? Is there some known workaround for manipulating the knock sensor's activities on older, noisier engines? Anyone else had to deal with this situation on an older brick?

Any help is greatly appreciated. I figure this might be a topic of interest given the age of many of the bricks owned by brickboard visitors.

Thanks,
-Rick





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