Does the Knock sensor really dectect a knock in the engine???
Is it like if the engine is running and I took a hammer and taped near the sensor, will that trigger it?


I got a engine that I think it spun a barring or something because its makeing a knock when its running and it has a perfect idle but when you push the gas that knocking noise comes out and the engine gets reall weak, like the computer is doing something because of that knock. When the knock goes away the engine idles well again.??????

 

It sounds like your knock sensor may be giving you issues. Have you checked for any codes?

You can tap on the engine block and the sensor will pick these up and translate ito an adjustment in your idle speed. To check your sensor you may want to disconnect it and take a voltmeter to it to check it out.

 

THe ECM "learns" knock in a very similar way that it "learns" to adjust the fuel curve. It has various "cells" in which it records and remembers knock. So if there's none at idle but there is at 2500 RPMs it will rember that and react accordingly under those different conditions.

Short answer: yes, your assumption is correct.

Now, you need to determine WHY you are getting knock when you come off idle. Is it REAL knock or is it some sort of false knock (loose engine bracket, exhaust hitting against the frame, etc.)

You can, FOR DIAGNOSTIC PURPOSES, deactivate the knock sensor by bypassing it and runnign the wire through a 3900 ohm resistor and then on to a good ground. ECM will think it's still connected but it will never hear any knock, even if there really is knock. You will want to reset the computer after you do this to reset the knock retard tables (or it will take about 1/2 hour of driving around under various load conditions for it to "unlearn" all the knock).

Now that you have no knock retard you can start diagnosing the problem. Mainly, is it REAL knock or is it something accidentally triggering the knock retard circuit?

 

ok well i guess you guys dont care but the engine this is on is a 96 nissan altima. I know you guys here are pretty reliable so I wannted to ask. I do for a fact know that its a real knock. its loud and the engine has no power and if you floor it it smokes like hell. Just yesterday the engine ran perfect, had lots of power and I came to a stop sign and it stalled, I went to start it and it was knocking like a bitch and had no power. the sound seems like its coming from the top of the engine, but i could be wrong it might be in the crank case.

well I guess ill have to go find a good Nissan board. lol I hope its as good as this one.