Scanning Knock

[EcoBoostSHO]

I received a PM asking how I was reading Knock with Torque (an android phone application that connects to an OBD2 reader through Bluetooth and returns multiple parameters) and my rather lengthy reply caused me to think I should probably put this out to the larger community to see if anyone else had any ideas.

 

Note - this has applications beyond Torque and could be used by just about any scanner that allows for custom PIDS.

 

Here is my original message:

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I'm happy to tell you what I think I've figured out so far but it isn't straightforward and I am still trying to determine if it actually IS the knock sensor PID. I found it on a list of extended PID's for the F150. There is definitely active data there and it does seem to be related to knock, but I get weird results at times which is why I haven't shared it with anyone publicly yet.

 

I believe the PID we are after is at 2203ec. You will need to go in to Torque to add a custom PID. Go into settings off the main screen and then select "Manage extra PIDs/Sensors". You will want to add a custom PID with the following parameters.

 

OBD2 Mode and PID: 2203ec

Long Name: Spark Retard (chose this because it was different than knock)

Min value: 0

Max value: 40

Scale: x1

Unit Type: deg

Equation: ((A*256)+B)/1024 (This is what gives me fits...I still don't have the scaling right)

 

That will get you some data but there is a catch (I believe). This PID seems to increment continuously when you are on the gas - almost like its doing something to tell you that the sensor is active (i.e. ready to go) so it knows it isn't "dead". The above equation gives you a number that will read zero at no throttle but light throttle gives you a number roughly 63.5 and then it starts decrementing...let off the gas and it returns to zero etc...

 

Now if you floor the car it will go to zero except when it gets actual knock and then it will give you a reading that I believe is fairly accurate...I sometimes get up to a degree of knock and then it seems to back off etc...Honestly at full throttle I hardly get any knock...but I can sometimes see some part throttle knock at 70-80 MPH highway speed cruising with the torque converter locked up.

 

If I back a couple of degrees of timing off the tune with my SCT programmer almost all of this "knock" goes away so I do believe this parameter is related to knock. I'm just not sure about my formula or how to get it to ignore the part that is continuously changing vs when it is measuring "real" knock.

 

I do know the SCT scanner will scan knock as well and if I had a way to hook them up simultaneously I could do some more side by side comparison...I suppose I could invest in a OBD Y cable and see if it works...

 

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Feel free to chime in if anyone has an idea!?

 

Thanks....