The following short article was written for me by my cousin who is 86 Years old. Even though he has untreatable cancer he still is sharp of mind and spirit. Please remember him in your dayly prayers, and I hope you learn as much from this article as I did.

Knock Sensor

A quick look at “spark-knock” fundamentals.

For the record we will say that the knock is a non-regulated quick rise in pressure generally confined to a pocket in the combustion chamber.

Now let us see if we can find out how this “quick rise in pressure” occurs. There are a number of ways but we will only mention two. One is a hot carbon spark setting off the mixture generally in the squish area of the head before the piston reaches top dead center of compression. That is rare these days.

The second would be low octane gas that ignites spontaneously at a low compression pressure. Even in today’s world of good grades of gas there are some combustion cavity shapes that are better than others so if one got a poor tank of gas knocking could come into play.

This quick rise in pressure from a sensor standpoint produces in the sensor a quick rise in both resistance and voltage. But the voltage can’t rise beyond the fixed ratio of the number of turns in the coil between the low voltage side and the high voltage side therefore the sensor can only sense a rise in resistance.

The ECU has a program to sense the rise in resistance from normal piston motion compressing the mixture. Anything below max RPM piston velocity will not trigger the knock sensor. But if a very quick rise in pressure from a knock occurs the sensor will sense both the rise in pressure and the resistance to the spark across the spark plug gap.

Even if the knock is not audible the sensor will indicate knock has occurred.

Now a loose wire will also be sensed as higher resistance to the battery voltage to the sensor. Its only way of telling you that something is wrong is to tell you knock has occurred. If there was a loose wire program it would indicate “loose wire” but since there is no such program it can’t tell you exactly what is wrong.

With this in mind a code H43 which is a knock sensor code may not necessarily mean the sensor is bad but rather a wire is loose or broken.

Author:
Leonard A. Karber

 

Thanks John. Very informative. My thoughts are with your cousin

 

 

Yup. The first time I got Code 43 it turned out to be oil and grime had corroded the sensor's electrical contacts. Prayers to your cousin.

 

John, your cousin sounds like a remarkable individual!

Let him know we on the Corvette Forum are rooting for him

Thanks

Jack