Knock sensor output inquiry (SAFC or datalogging users may be useful here)

IwantMKIII

WVU MAEngineering
Jun 12, 2007
2,477
0
0
Perkasie, PA
Some of you know for a long time I've had mysterious power loss at op temps. While I had suspicions of my knock sensors, I never really thought to just monitor the knock reading on SAFC. I have been monitoring the output now for several weeks and this is what I've noticed. Please let me know a few things if you have the knowledge:

-Normal operating ranges for the knock
-Your knock levels at different ambient temps; is this normal for others?

An odd characteristic I have noticed is the output seems to maintain a baseline. For instance, initial startup to just before op temp, typical outputs are 30-60 range. This range is somewhat steady at an idle and maintaining speed, under boost obviously things go a bit haywire. As driving continues this 'baseline' increases anywhere from 70-200. I have correlated significant power/acceleration and responsiveness loss as this 'baseline' increases. I suspect while just hitting OP-temp the engine bay is still reasonably cool, as the heat soak increases, so does the 'baseline'. This characteristic is further influenced by ambient temps. Hotter days 90+ (we have fairly significant humidity here too) the baseline hits 150 and up with increasing temps; warm nights around 100 'baseline'

Typical Ranges:

Cold Start: 30-40
Warming up: 30-60
Op temp inital: 60-80
Op temp long term (20 min+; heatsoaked): 90-130
Op temp long term (heatsoak plus high ambient temps): 130-200

The other odd part I find is once it hits these 'baselines' it never goes down, even with ignition off, the SAFC still reads the baseline; the power must be completely turned off to the SAFC before it stops reading. Could this be the SAFC? Possibly, but its still a reading correlating to significantly diminished power.

Also notable, as this increases, my tendency to afterfire significantly increases from nearly never to often. Base timing is spot on 10* and no codes of course.

*There is next to no information about the knock sensors in the TSRM and I find no typical operating values as a base comparison
**3P, if you come across this, any input? You have significant knowledge about the CPU and how it operates.
***Those with SAFC can check these values under the sensor check menu