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Speedometer Calibration

Yahoo Message Number: 71478
This time I think I have a stumper.
If you remember earlier in the year, I purchased new TOYOs for my '04 Inspire. The new tires were over sized as TOYO no longer made the originals. Obviously, my speedometer and odometer are off. As it turns out, it is almost, exactly 10%.
My mechanic has been unable to find out how to re-calibrate. Although it's not the end of the world, it is a PITA calculating fuel consumption and keeping track of actual mileage. So far I've been using my GPS for the info.
Anyone out there know the method or at least who to turn to for help?

As always, many thanks in advance.

George

Re: Speedometer Calibration

Reply #1 –
Yahoo Message Number: 71479
George:

Try contacting Chris Snyder (520-665-1014) or John Davis (541-693-3015)

Kevin Waite
541-953-6162

Re: Speedometer Calibration

Reply #4 –
Yahoo Message Number: 71488
George,

On most newer vehicles, the speedometers are electronic. The ECM sends a signal to the speedometer. This signal or pulse is adjusted in the ECM. Based on tire size, etc you set the revs per mile in the ecm. Or in your case, knowing it is exactly 10% reduce the revs per mile by 10%.

Mikee

Re: Speedometer Calibration

Reply #5 –
Yahoo Message Number: 71497
Mikee,

Sure wish I knew what an ECM is, I'm thinking electronic control module but that's all. Waht and where is it or how do I access it?
I'm told it can be recelibrated with the switches on the rear of the speedometer but need to call the manufacturer with the tire sizes to get the code.

George

Re: Speedometer Calibration

Reply #6 –
Yahoo Message Number: 71498
George,

That is in fact what ECM stands for. On a Caterpillar it is mounted on the pass side of the motor. You have to have some type of a interface like a computer that plugs into it's access port. I'm going to access mine on Monday so I will look if there are any parameters you can change on my Caterpillar ECM. I don't know what engine you have but it's probably similar. However, I have heard of the switches on the back of the speedometer that you can physically change. Good Luck! Kevin Burns

00 Affinity 5865

Re: Speedometer Calibration

Reply #7 –
Yahoo Message Number: 71499
Kevin,

I have my laptop plugged in for my Silverleaf. Can I access the ECM that way?

George

Re: Speedometer Calibration

Reply #8 –
Yahoo Message Number: 71502
I'm not absolutely sure this applies to all CC models but I think that for those vehicles that have analog display dash instruments that the speedometer is independent of the ECM (Electronic Control Module). The electronic speedometer with its analog display gets its signal from a magnetic pickup mounted by the left front wheel. The back of the speedometer housing in the dash has provisions for calibrating for different tire sizes. I don't remember the details of exactly how to do this but I think it was using a series of tiny switches.
On the other hand the Featherlite digital display module does take its data from the ECM and uses the speed sensing of the Allison transmission from the rear and also has a provision for making calibration adjustments in the setup mode. The two systems are not connected. In other words if you change your tire size circumference you need to calibrate both separately for them to be in complete agreement and accurate. The situation is analogous to the other factory analog dash instruments where their input information comes from different input sources than the Featherlite digital display which takes its input the ECM.
If, for example, your coach came with 12R22.5 tires and was calibrated for such then if for some reason you replaced all the rear tires with a close but not exactly identical metric equivalent size you will find that your analog dash speedo information getting its input from the 12R22.5 front is slightly out of agreement with your Featherlite digital display getting its input from the ECM and transmission. The difference in my case was about 1%. It is, of course, possible to adjust the Featherlite display to correct.
Those vehicles that have digital displays driven by the Featherlite technology maybe are completely driven by the ECM outputs.

Jim M

'02 Intrigue #11410 ISL 400

Re: Speedometer Calibration

Reply #9 –
Yahoo Message Number: 71506
George:

Your calabration circumstance got me to thinking.
For the past 15 years of motor homing I have not used the dash mounted speedometer. particularly in my current coach of 11 years use.
Between my body geometry and my selected steering wheel position I cannot conveniently see the speedometer.
My solution for the problem has been to depend on the GPS spead reading as displayed on my 15" flat screen monitor. This also is displaying my trip information. I use the DeLorme software.
I appreciate this may not be for everyone but at a glance I have a very accurate number and I do not have to judge if it is above or below where I want to be. I can make the numbers as large as needed for easy reading.

just another way to do something.

James M. Green Intrigue 11021 "Rollingghetto"

Re: Speedometer Calibration

Reply #11 –
Yahoo Message Number: 71515
Jim,

I agree and use the Silverleaf now as I drive. However, it's a lot of extra work to calculate MPG as opposed to reading from odometer. Also, after an extended time mileage on odometer with it's false reading would be a turn off to a perspective buyer.

George

Re: Speedometer Calibration

Reply #12 –
Yahoo Message Number: 71516
George,

See message #67451 and related posts for information on programming the Teleflex electronic speedometer. This may be what you're looking for.
The message attachments in the (Jan 2011) discussion thread should probably be copied into the files section of the forum for future ease of access.
--

Tom Harsch 2002 Allure #30791
Rapid City, SD

Re: Speedometer Calibration

Reply #13 –
Yahoo Message Number: 71517
ECM is Engine Control Module. You cannot access it, unless you spend the bucks for the program and cables.
You may have a speedo that has dip switches on the back to change its calibration. Yours may be ecm driven or dip switch.

Mikee

Re: Speedometer Calibration

Reply #15 –
Yahoo Message Number: 71519
Tom,

Thanks, I remember that post from back when I was buying the tires. Now if I only had any idea what the heck the charts mean, I'd be in good shape.
I'm going to call the speedo manufacturer tomorrow. I understand they can give me the dip switch setting with my tire info.

Keep your fingers crossed.

Georhe

Re: Speedometer Calibration

Reply #16 –
Yahoo Message Number: 71547
You would need to take it to a shop the have the ECM re-programed, I have the Cummins and had some problems with the Cruise Control, I had some work done by Cummins and what they did screwed up my cruise control. Long story, but I went to a private owned but cummins authorized shop and they plugged the computer into the ECM and I watched as he checked all the Parameters, and I was supprized as to how many were programed wrong or not on at all., Mine was programed for a Manual transmission....It is not rocket science, just a computer with the Right Program... Now I am not up to speed on the Cat Stuff..so it may be totally different... but Tire size is in My ECM... I think there is a copy of the Parameters in the File section for the Cummins..
Marvin, 07 Allure 470, #31459
M

Speedometer

Reply #17 –
Yahoo Message Number: 71505
The speedometer on our 2004 Magna does not give accurate readings. When we start out in the morning, it may read 5 MPH over the actual speed on the Silverleaf and GPS, and then will drop to 5 MPH under the alternative units. The drop is quick. The speedometer never gives the correct speed. Mostly, it gives a low reading. There seems to be no rhyme nor reason for the timing of the drift from a high to low reading. I have not changed the tire size. Any ideas as to what might be going on would be appreciated.

Paul Onerheim
2004 Magna 6301