This all started early in the week. I had an O2 sensor go bad that did throw a code right away but ideal was ruff and it had knock and miss fire. After it threw the code a swapped them and the code followed the sensor so I changed it out. No more code but now I still have 9 degrees of knock at 2000RPM on hard acceleration or rap of the throttle after the car warms up. I changed out the plugs today thinking they might have got jacked due to the bad sensor. But the knock remains. It also has an intake back fire. Wires are fine I checked them all when I did the plugs coil is good, I have a spare so I checked it as well. No arcs under the hood, ideal is fine, no leaks at the intake, and all the vacuum hose are good.

94 a4, opti is about 7 or 8 years old and I have an electric water pump so it not leaking on it. Any ideals??? I'm thinking opti again, but I don't want to throw a new opti if someone has another suggestion.

 

Try running some high-octane unleaded race fuel and see if the knock goes away. That will tell you if it's real knock or false knock.

 

Diagnosing problems on the LT1 is so easy. You can ALWAYS just blame it on the opti!

See if you have a plug wire touching or close to the knock sensor wire. Also make sure the little block ground wire is tight (by the starter), and the main ground cable (by passenger side engine mount), and the ground strap by the coil.

 

I changed out the starter not to long ago so this maybe a good place to start. The grounding staps (there are two) by the coil is good for sure. I'll check the one by the motor mount (two there as well), but I'm not sure where the one is by the the starter??? Do you mean the small wire that goes to the starter itself or is there another one down there? I've had this car for ALONG time and I hate to admit it but I'm not sure where the knock sensor wire is...LOL

 

The knock sensor screws into the hole for the block drain plug, on the passenger side, right by the motor mount. A loose motor mount might cause problems.

Courtesy of Shoebox:

http://shbox.com/1/ks.jpg

 

Got it. I thought that might be it but wasn't sure.

When you say a loose motor mount might cause problem do you mean with what I have going on?? I can check 'em. Never really thought of that.

 

The knock sensor is a microphone attached to the block. The motor mount is right next to the knock sensor, mounted to the block. Any rattling in the motor mount is going to be picked up by the knock sensor.