knock gauge vs scanmaster

[ed39]

so i had a 2 pod a pillar and was sick of looking at the empty hole so i threw a knock gauge in that i had.... the scan master dose not show knock but the knock gauge shows knock....which do i believe haha the car seems to be running perfect

[Keller]

Originally Posted by ed39

which do i believe

Maybe both!

Remember, your Scanmaster only reads a group of data every 1.6 seconds. Consider each frame a mere snapshot. So it can miss some knock here and there. The knock alert is connected all of the time. A small amount of knock could come and go and never register on the Scanmaster at all!

Tools like DirectScan and PowerLogger will pick up pretty much everything, since they collect many frames per second.

That being said, the knock alert may be set to be more sensitive than the car's filter would typically register as well. Only comparing to one of the more real-time tools would help you understand that better.

[ed39]

hmmm..ill hook up an otc 4000 today then thanks!

[Keller]

The OTC will show the same data as the Scanmaster. The DirectScan and PowerLogger attach to a different connection inside the ECM and get data at many frames per second (16-18 fps) for much higher resolution.

[Mountain GN]

Originally Posted by Keller

Maybe both!

Remember, your Scanmaster only reads a group of data every 1.6 seconds. Consider each frame a mere snapshot. So it can miss some knock here and there. The knock alert is connected all of the time. A small amount of knock could come and go and never register on the Scanmaster at all!

Tools like DirectScan and PowerLogger will pick up pretty much everything, since they collect many frames per second.

That being said, the knock alert may be set to be more sensitive than the car's filter would typically register as well. Only comparing to one of the more real-time tools would help you understand that better.

Quoted for truth.

I run a knock gauge and a Scanmaster, and on the rare occasions that I do see knock, it's usually on the gauge ONLY and sometimes on both.

I think that, unless you can roll with a laptop all the time, having both of these tools is important to peace of mind.

[kenmosher]

The gauge is basically showing the status of the knock sensor line ... and it's only one part of what the ECM uses to determine whether or not to retard the timing.

That input is "filtered" for duration, frequency, etc. and added to other factors (such as load, RPM, etc.) in the ECM to determine whether it's "false" knock, transitory, noise, etc.. Using all these things as part of the algorithm in conjunction with the calibration tables (knock attack/decay rate, timing desired, etc.) it will "decide" whether to retard the timing or not in response. It may decide to not retard the timing depending on the event ... add to that the scanning speed and you may not see a very quick "blip" of retard.

[ed39]

nice write up ken... made me understand better...well it was knock thats for sure i could hear it..not good. i was tunning the alky chip thats why i was so confused cause the scanmaster wouldnt show it. but i have the car 80 percent dialed in ran 12.9 @106 tonight spinnging the DRs out of the hole . but i wanna fine tune it lock the converter and launch it better