knock sensor test

I have been lurking for some time, but have not posted. I find this site to be a wealth of information.

I suspect a faulty knock sensor on my 1999 Suburbank 1500 2wd. It is running the way others here have described: a noise that sounds like detonation is audible when accelerating under load from about 1300 to 2000rpm. I have not seen a 'service engine soon' light come on. I suspected plugs and wires to be the problem after seeing spark travelling along the outside of the wires and around the plugs after dark the other night and replaced them. I used AC/Delco plugs and Bosch wires. The noise is still present.

I have heard that you can check the knock sensor's function by tapping on the engine while it is idling and listening for the engine sound to change. Has anyone else heard this? I tried it today, tapping with a small steel pry-bar and did not hear any noticeable change in the engine tone.
I would imagine that a bad knock sensor would show up as a diagnotic code, but I don't have access to a code-reader, nor the funds to buy one right now, so unless I can get the dealer or someone else to look at the codes for free, checking it via that method would be difficult.

Any help would be appreciated.

I have a 1998 Suburban that was acting like yours with the pinging. For the most part, putting in 89 octane fixed it, until I started pulling a fairly weighty trailer.

I thought it may be my knock sensor as well, but it wasn't. You can remove it and have AutoZone test it for free. That wasn't my problem. CAUTION: The knock sensor is also the drain plug for the coolant in the engine block...so have a pan ready. The knock sensor is on the back, right, bottom side of the motor.

Here's what I did to fix it. I replaced my factory 195 degree thermostat with a 170 degree one to help it run a bit cooler and avoid the pre-detonation. That pretty much did the trick. Now I run 87 and the 'burb doesn't ping anymore.

Hope this helps.