TC Slip PID in OBD Fusion App

[1997ThunderbirdLXV6]

Inspired by @theterminator93 's response to @GRWeldon 's thread, I went ahead and added the Ford TC slip PID to my dashboard in OBD Fusion.


The Good

At steady cruising in 3rd or 4th over 40 mph, slip reads anywhere between 0 and 4 RPM, with rare spikes to 6 or 7 RPM. That sounds just about right.

At anything other than steady cruising, such as acceleration or driving in lower gears, slip fluctuates a lot, too much so to make exact sense of it, though it appears within an expected range (couple hundred RPM).


The Odd

Where the data falls apart is at a standstill. Logically, at 0 MPH, I would assume that TC slip should be = engine RPM. Wouldn't that make sense? Or am I missing something here?

Instead, the app shows TC slip at more than twice the engine RPM. Can anyone explain this? Or is it likely a programming mistake in the app?


I did take screen shots and can post them on request, but they really don't add any further intel.

 

[1997ThunderbirdLXV6]

...so I'm guessing nobody knows or cares. Granted I guess the main thing is that slip is 0 or close to 0 during TCC lockup, which is the case.

But the geek in me wants to understand the display values when it's  not locked up.

 

[theterminator93]

I don't have/use these types of apps - I still use the antiquated laptop + XCal2 datalogging method.

My guess is there's some generic formula in the app that applies to the raw data from the bus which works for "most" applications but with our early OBD-II designs isn't quite the same. It might also be calculating the data using different data sources than the LiveLink PIDs which produces a different result, especially if one of the data sources used in the calculation is extrapolated data from other sources due to said data source not existing on our PCMs.

Without the duty cycle PID I agree that the most important takeaway is nominal levels of slip during cruise. The slip during acceleration seems high at first glance but may be commanded (again, no way to know without the duty cycle PID).