The 5.7L engine in most 1990 Chevrolet Silverado vehicles uses a knock sensor on the engine block. This sensor tells the engine's computer if the engine isn't getting enough spark, a condition which causes a knocking sound in the engine. The sensor tells the computer to advance or retard the timing accordingly, helping the engine function properly. If the sensor goes out and the engine doesn't get enough spark, it could suffer damage.
Lift up the front of the truck with the jack. Put a pair of jack stands underneath the frame and lower the jack onto the stands.
Locate the knock sensor, which is forward of the starter on the passenger side of the engine block. Disconnect the electrical connection with an open-end wrench, then remove the sensor using a different wrench.
Wrap the teflon tape around the threads on the replacement knock sensor. Install the sensor into the block using an open-end wrench. Reinstall the electrical connection, then lower the truck off of the jack stands with the jack.
