I am suddenly (never before) getting audible knock and freescan is showing knock retard at light to moderate throttle... I logged a 5 minute drive around my neighborhood and saved it as a .csv file. I've read injuneer's website and for the most part my numbers look normal to me...

With a 10ms sampling rate,

Left o2 averaged .465
Right o2 averaged .492

Left BLM averaged 114
Right BLM averaged 113

Left integrator averaged 125
Right integrator averaged 125

I can email the data file if anyone wants to look at it...

Any Ideas as to what is causing this knock? Maybe just bad gas? It didn't start right after filling the tank... I have about a half tank left...

One other thing worth mentioning is that when the motor is hot, there's a rattle in the exhaust that sounds like it is coming from the CAT. It was suggested to me that the CAT may be restricting the exhaust flow and be partially blocked...

My Z has a little over 152K miles and is a 94.

Thanks for any help.

 

Can you pinpoint where the noise is coming from. EX: undervalve cover, exhaust, air valves, etc.

 

I can't be specific on the knock. as it only happens when I'm driving and try to accellerate... It sounds like it's coming from the drivers side, but that can be deceiving...

The other rattling sound I'm pretty sure is coming from the exhaust near the CAT... I need to jack up the car and see if anything is loose.

 

If you could get the car on something safely and run the car with the back wheels free you may be able to pinpoint it exactly. Does it make any noise with just reving the motor? A mechanic was able to drill a hole where the cat is and test the cat to be sure it isn't plugged or falling apart.