I have an automatic 9-3 Aero, and I want to try and see if the clutch slipping is normal or whether I have an issue. I am aware that in first and second the clutch intentionally slips to smooth out the drive before locking, then in third and fourth it locks immediately to put drive power through.

What I had planned to do was log RPM against speed via TorquePro Android app. My theory was that when the car is locked into a gear, the speed and RPM would increase at a fixed ratio (the gear ratio). If the clutch is slipping, the ratio would be ever changing.

So plotting speed divided by RPM I expected to see a series of five horizontal lines, each one corresponding with each gear but changing maybe half a dozen times in the journey (it was a fairly steady drive in a 30, then a 40, then NSL, then back to 30). Instead it goes up and down like a yoyo. As far as I know it's not changing gear that often, so does that mean I do actually have a slipping clutch, or is my test method flawed?

I can't watch this happen in realtime as I need to be driving, I also can't tell what's happening by ear as I can't tell whether it's an intentional shift or the clutch is slipping.

(By the way, I am aware that it's a torque converter rather than a clutch, but there's more letters to be typed in clutch converter!).

the method of testing seems sound to me.

when you are monitoring speed, is this from the obd, or gps?
I tried logging both gps and obd speeds, and gps ones seem to lag.

also note the odb mph is calculated from the kmh value. so goes in steps of about 0.6mph

It was OBD, I did notice it was kmh although that should just change the numbers rather than the graph itself.

I'll have to take it for more of a run and see if the graph makes more sense.

Are you referring to the lock up clutch within the torque converter? They are normally only engaged under cruise conditions.

I thought it would lock during hard acceleration as well? Or does it just rely on friction to transfer torque?

I created a website mainly for my own amusement that can draw graphs from Torque (and MSDroid/TunerStudio) along with a map. Give it a go, and if it doesn't work send me the log file so I can debug it

https://scudderfish.github.io/LogViewer