Where is the knock sensor located on a 1990 Chevrolet pickup 4 wheel drive?

The exact location of the knock sensor on a 1990 Chevrolet 4x4 pickup will depend on the engine. Chevrolet trucks from that year used several different V6 and V8 engines. There's no single answer.

To find it, you'll need to:

1. Identify your engine: Check the engine bay for an engine code (usually a stamped code on a metal plate near the valve cover). This code will help you pinpoint the specific engine.

2. Consult a repair manual: Once you know the engine, obtain a repair manual specifically for your year, make, model, and engine. These manuals have detailed diagrams showing the location of all sensors, including the knock sensor. Chilton's, Haynes, and factory service manuals are good options.

3. Look for it near the engine block: Knock sensors are typically mounted on the engine block, often near the bottom, somewhere close to the cylinders. They are usually threaded and relatively small.

Without knowing your specific engine, I cannot provide a more precise location. Trying to find it without a repair manual is difficult and could lead to wasted time. The repair manual will save you a lot of frustration.