KR-Graph4: What the PCM Believes to Be Real Knock

Oct 12, 2011

Now, is this noise floor parameter REALLY “fixing” KR? Is it really ELIMINATING KR? No, absolutely not. What it is doing is simply masking KR up to a 1 volt. Notice that these graphs indicate by definition that this is a FALSE KR. It is a KR that jumps immediately to a BIG value and then recovers to 0 as the engine’s RPM increases. It appears that this parameter does MORE than just mask KR up to 1 volt because it is SO much harder for KR to be generated in the car. Unfortunately, information about this particular parameter is limited, and it is currently unknown what it really does. I can say, that the system still detects knock at all levels above a volt (I can generate KR from 1 degree up to 15 degrees). When I add timing without race gas, I start to see KR at around 6 added degrees pretty easily (23 degrees overall ignition timing), so the system is working and working well. I have had this change to the PCM since October of 2002 with no ill effects in about 5,000 miles of driving (I put on a lot of miles). The fact that my heavy KR started immediately after my transmission rebuild also lends itself to false knock (extra noise generated by the transmission).

The bottom line for this mod is this: it should NOT be your first mod, but if you have tried everything else and have similar KR issues that I have described (large KR spikes in small pedal travel that recovers as engine RPM increases), then you may want to look into this one. If I didn’t have this one done, I would not be able to run at the track very well at all. With the help of this PCM change by DHP, my vehicle is running between 12.62 and 12.84 at the track.