SpecRacer.com

I have a SPEED reading off the ECU, going into my AIM data acquisition. It's reading a transmission speed sensor, and I compare that speed with GPS speed to detect rear wheel lockup.

Problem: SPEED reads a multiple of actual (GPS) speed, and that multiple seems to change every weekend (but is consistent for any given weekend, across sessions).

I'm thinking there is some setting somewhere that gives the ECU tire diameter or something like that, but i have no idea why it would change over time.

Any ideas/knowledge on this topic?

Thank you, and Happy New Year!

In the Pe3Monitor, under Tuning, select Speed Limiter. I don't recall the default values, but I believe the important value is "Distance Per Tire Rev(in)", which should be in the range of 70.5 (or whatever gets you close to GPS speed). If this is already close, check the value in Pulses Per Tire Rev. I think the correct value is 12. If these are way off (e.g. the default for Distance Per Tire Rev when not connected is 26.2) that could affect the generated speed. Doesn't explain why this would vary over time unless the VSS is bad or there's a connection issue that would cause a pulse detection problem.