Fine Tuning the 6.5's Speedometer

[JayTheCPA]

Scenario in my Burb:
> OE size tires.
> GPS indicates 50 MPH.
> ECM reports a calibrated speed of 50 MPH (per my Edge which knows the tire size).
> Speedometer indicates 48 MPH.
> The 2 MPH gap is consistent at all speeds (otherwise I would have suspected the VSSB or tire diameter).

Sure, 2 MPH is easy enough to mentally adjust. Preference is to dial-in the speedometer.

Is there any way to re-align the speedo? Or an offset in the ECM's code?

 

[Will L.]

First verify against actual miles driven, not all gps are correct. Drive 10 miles or so on the highway and check that against the odometer.

If it is off...http://www.thetruckstop.us/forum/showthread.php?39083-Programable-VSSB&highlight=vssb

 

[JayTheCPA]

First verify against actual miles driven, not all gps are correct.

Completely understand about GPS lag. 'Instant' speeds were measured on flat, nearly level, and straight ground after establishing / holding the speed. Suspicions first started when I drove past stationary / permanent RADAR installations (the 'Your Speed Is XX' type of unit).