If the knock module compensates for spark knock and can retard timing up to 15 degrees, is there any damage done if pre-detonation does not induce enough knock to trigger spark retard beyond that limit?

I did see a post containing a picture of the melted edge of a piston which terminated in zero compression for that cylinder. This makes me wonder if the pre-ignition was producing an audible engine knock that was simply ignored or can premature detonation go undetected and become a silent engine killer.

 

I had detonation in my LT-1 so bad that the knock module couldn't retard the timing enough to compensate. Then again, I was running a SC when the engine was bone stock...

 

Can you tell me more? How long was it detonating; did you have any engine failure because of it? How did you fix it? Thanks!

 

Yea, how many miles, how much boost, and it wasn't intercooled right?

 

The knock module doesn't do any of what you described.... it doesn't "compensate" for knock and it doens't retard the timing. The knock sensor is a microphone. It sends the noise signals to the PCM. In the PCM the knock module filters out noises that the module is tuned to filter out, because it knows they are mechanical engine noises, and not knock. After processing the signal, the PCM does the knock retard calculation and retards the timing.

I'm also not sure what you mean by "pre-detonation". There's pre-igintion (ping - combustion occuring before the plug fires) and detonation (knock - a second flame front, developing after the plug fires, as a result of the end-gasses formed by the initial combustion). The most common problem is detonation. The knock sensor is capable of detecting the sound of detonation before you can hear it, and the PCM pulls the timing very rapidly (attack), in very large steps.... in effect over-compensation for knock. The PCM then puts the timing back in in smaller steps (decay), and more slowly. All that assumes that a "tuner" hasn't altered your PCM to reduce the attack and delay, or reduced the upper limit for knock retard.

If you can actually hear detonation, you have a problem. If its severe enough, you will lose a ring land, a piston or burn a hole in the head. Will it be instantaneous.... not likely in an NA engine, but always possible in engines running large amounts of nitrous or very high boost.

 

My question was really a simple one. I had hoped to learn if the (pcm) adjustments to the timing were enough to protect the engine from damage or if some level of damage may have occurred anyway. The computer has the ability to pull up to 15 degrees. Since my scanmaster indicates only 9 degrees of spark retard I was (hoping) wondering if that indicates that the detonation was not so severe that the computer could still protect the engine at that level. The detonation was discovered on a nitrous run and I have made several runs like it before I had the scanmaster to tell me I was experiencing this pre-ignition. I have never heard or felt anything to tell me there was a problem but now am wondering if there is some level of damage.

I wasn't trying to teach anything and my question is an admittance that I'm ignorant. To me, "pre-detonation" just means the same thing as pre-ignition. I guess not though. I figured we all know that the pcm commands the spark timing. I just referred to the knock module doing the work because without it the pcm would not be able to get the signal that there was a problem. I guess I failed to make a sensible question because of the improper words and terms. Your answer indicates that all those mistakes were distracting or the terms were so confusing that my question was incomprehensible. But from your last sentence I think I'm okay. I was only using 125 hp shot and it lasted for just seconds. I don't take the car much over 70 on the express way when testing the system. This is just out of 2nd gear. I don't know if this is any more clear or not. Thanks.