I have a 2002 gmc sierra that needs a knock sensor. The motor is a 4.3L and I cannot manage to find the knock sensor location

Look on the front of the engine block--above and to the right of the crankshaft pulley. On FWD cars, they are frequently mounted in the forward side of the engine block, near the oil filter and under the exhaust manifold. I give these as ideas where to look. They are not a little, sensitive sensor. Removal should not be a problem, once you locate it.

It should look something like this:

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