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VMS Data

August 29, 2013, 01:01:04 pm

Cummins M11

On our last rig the VMS data was right on. On this one, Three readouts apparently are wrong.

MPH: When running at 60 mph on the dash speedometer, two GPS units (Tom Tom & phone) agree that we are traveling at 60. The VMS shows 62. The only thing I can think of is tires. We are running the right size (275/80) Continentals (what Wayne at FT refers to as "trailer tires"). I know I can add a 3% multiplier to the VMS to compensate and that would fix the readout but I'm curious as to why it would be off. Continentals slightly smaller?

ODOMETER: The dash (mechanical) shows 103,228; the VMS shows 108,031. Almost a 5% difference.

ENGINE HOURS: Way off. The gauge in the back shows 1,325 hours and the VMS, 2,193. I haven't checked the back gauge to see if it's working but it may not be as those hours would yield a 78 mph average. This engine is no dog but that's sounds pretty darn optimistic!

Just looking for ideas. Thanks.
jor

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Re: VMS Data

Reply #1 – August 29, 2013, 01:10:06 pm

You can fine tune the readout to make it accurate.  Look in the manual and it tells you how.  If you don't have the manual it's on the Silverleaf website.  This is from my manual.

Engine Corrections
Generally the data displayed by VMSpc is extremely accurate. But an improperly
calibrated engine may send speed, distance, and fuel information that is consistently wrong.
For example, if you put larger or smaller tires on the coach, the speed and odometer data will
clearly be incorrect.
To compensate for this kind of error you can enter correction values in the Engine
Corrections dialog box. For the odometer, hourmeter, and fuelmeter you can enter both an
"Offset" and a "Multiplier". VMSpc will automatically add the Offset to the indicated meter,
then Multiply the result by the multiplier. In addition, the multiplier will be applied as appropriate
to the Speed, Cruise Speed, MPG, Fuel Rate, and Rolling MPG gauges.
For example, if your engine was reprogrammed and lost its history at the 20,000 mile
mark, and you added tires that cause it to understate the speed by 5%, change the Odometer
Multiplier to 1.05. Change the Offset to 19,408. (Remember that the Offset is added, then the
Multiplier is applied. 19,408 * 1.05 = 20,000.)
In addition to the engine corrections, this option also allows you to adjust the sensitivity
of the Rolling MPG reading. By placing a larger number in the "Rolling MPG Buffer Size" you
can increase the time window used for calculating the Rolling MPG, thus making it respond
more slowly. A lower number will make it respond faster, making the gauge fl uctuate more.
The Odometer PID setting is intended for the few engines which do not report their
odometer readings with PID 245. If your trip odometers and other features do not report correctly,
you may need to change this value from 245 to 244.

Keith

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