What causes this? I can hear the motor pinging (the rocks in a tin can sound) but the PCM doesn't pull any timing.

 

sounds like Detonation, Not good. Stop throwing rocks under the hood! Just kidding. Probably lack of fuel, But what the hell do I know.

 

Did you adjust the kr settings?

 

No, I've never messed with them.

 

The two times that I have heard audible knock, the scanner showed 0. I have talked to others that have exprienced this as well. You are not alone my friend. This is on stock KR settings as well.

 

I've heard of this before too...funny how the PCM will see false knock but not real detonation...sometimes I wonder about the effectiveness of the GM knock sensors. Depending on how the sensors were installed, they may be somehow de-sensitized (sometimes guys install them with teflon or RTV on the threads and it de-sensitizes them). The pinging could be caused by a number of things...lean mixture, high cylinder temps, carbon buildup, too much timing, etc.

 

My truck does the same thing! Sometimes even when I use 93 Octane and Octane booster, under WOT I'll still hear some Spark Knock. What Gives?

 

My co-workers 2004 vette does this as well. It's a bone stock tune too. We've logged this, and he'll get some audible pinging and then the kr kicks in. And even then I don't know where the kr is coming from. His timing isn't all that high for a N/A engine, but for some reason it'll ping and the PCM doesn't know it until it's too late.

 

I had this same problem. Turns out the "knock" was a faulty lifter that would cause the valve train to rattle only when under certain load conditions. Sounded just like a detonation knock. New lifters and the problem went away.

 

For the folks who have real pinging and everything else checks out (premium fuel, not lean, timing OK, not running warm, etc), you could try the old Seafoam treatment to clean some of the carbon out of the combution chambers...it may help. Do a search for "Seafoam" and a bunch of stuff should come up