Thread: knock sensor location

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I've installed knock sensors in engines that never had them. I've even had to external mount them on a bracket. As long as the mount point is VERY solid to (or in) the block, they seem to work OK. Most knock sensors are tuned for the bore diameter/ring frequency of the engine. As the bore gets larger, the sensor is set to respond at lower frequency.

That's why it's important to have a good solid mount. If you accidentally create a knock sensor mount condition that vibrates at the normal frequency of the selected sensor, it'll be "over excited" by other inputs. Your clue will be continuously retarded timing. To test for "over excited" output, hook two 1-watt, 1.5-2.1 volt Zener diodes "end to opposite end, side by side". That means the ring on the diodes are at opposite ends, with the wires soldered together at each end of the Zener diodes (they are lying side-by-side). Connect one end of the package to the knock sensor output, and the other end to ground. If your engine wakes up and the timing advances, you have a knock sensor "over output" condition. The Zener diodes can't hold more than .5 volt when reverse biased. By putting them opposite each other, you drain the AC signal output to ground at 1 volt peak to peak (both the positive and negative wave), which the ECM sees as OK with zero knock. Use this ONLY to test, not to drive everyday. If it starts to ping, the ECM won't hear it.

I've seen installations that were a little sensitive, and the timing would retard from a loose alternator mount or bad water pump bearing! Also watch out for "soft" mounting, caused by installing the sensor into heavily painted threads (common on factory replacement blocks) or onto something floating on FIPG. That will make the sensor under respond, and may be detected as a fault by the system.

Good luck with your project.

I have decided to add a 45 degree elbow to the block then screw the sensor into that. I hope that the additional length does not effect the frequency which the sensor tries to detect.

Attached is a picture of the clearance issue