adjusting speedo

[XTR2Turbo]

My car is displaying 50mph when I am travelling at 55mph as displayed by the satnav.

It has the standard white Ultima analogue gauges.

I did not build the car so don't have the instructions for the gauges.

Please could someone advise how to adjust.

Thanks

David

[V8Dom]

not sure but most speedos on production cars are designed to be under speed by 5-7% so there is a safe side to speedo readings against being pulled by Police and you claim speedo said.....

I know its 10% but better it shows fast than slow..

I have gps heads up display which is spot on if i want to know my speed..

What wheel/ tyre size are you running as different size tyres effect speedo readings.

Dom

[XTR2Turbo]

My speedo is out the wrong way though. From what you say it should be showing 60 when travelling at 56 but it is showing 50.

[Gulf LS3]

Hi

You can calibrate the speedo by adjusting the input values, i would suggest a call to the factory to see what values you need. How many teeth do you have on the speedo trigger wheel?

[XTR2Turbo]

thanks

yep happy to calculate the value. Is there a button combination that brings this up?

[Steve_D]

I've only done it once so may have this wrong.
Hold the trip zero button in and turn on the ignition. Release button.
I think the first of 4 digits will be flashing. Keep pressing the button until the number you want is displayed. After a pause the next digit will start flashing so you repeat the process until you have done all 4.

The book says 6400 for the external trigger wheel on the drive shaft and 7800 if you are using the sensor inside the gearbox.

If that number is not correct for you, perhaps due to different tyres, then you will have to take a SWAG at what the input number should be.

Steve






Technical term definition.
SWAG Scientific Wild Arse Guess

[XTR2Turbo]

thank you

I'll see what mine has at the moment and adjust accordingly

David

[V8Dom]

Steve_D said:

Technical term definition.
SWAG Scientific Wild Arse Guess

thought SWAG was a slutty wife and girlfriend..

maybe too many years in Cheshire.

Dom

[ROWDYRENAULT]

using the method that steve suggested on some of the factory speedos Im not sure if it's true for all of them, you can change the value shown up or down and get as close as your outside data is accurate. here in California we have remote unmanned radar units that flash the speed you are going to remind you to slow down. I have one of these very near my house and was able to get the error to 0, at least according to that remote unit and a couple of others that I have driven through. For you Brits that can be a devious lot when you want to be the answer is NO if you go through these units over a preset limit it just flashs all the lights at you. So the answer is no we don't run bets on who can get the highest reading. Although it would be fun. Lee

[XTR2Turbo]

Thanks

My car had 6400 in it.

I assume increasing the number will increase the speed displayed and decreasing will reduce.

I will make some changes and test

[ROWDYRENAULT]

David don't be to subtle with the number changes. Takes at least changes in the 10s to make a difference. Lee

[YIIHAA]

XTR2Turbo said:

Thanks

I assume increasing the number will increase the speed displayed and decreasing will reduce.

Other way round. The number is "pulses per mile".

So at the moment when you are doing 55mph the speedo is receiving (6400*50) pulses per hour = 320000. You know that that number of pulses per hour actually represents 55 miles, so the correct pulses per mile = (320000 / 55) = 5818

[YIIHAA]

Just remembered something else. Whilst the number does represent "pulses per mile" the Ultima "200mph" speedo certainly used to be a VDO 160mph speedo with a new face. So if you did the calculation by counting the tabs on the sensor wheel and used the wheel circumference you would need to adjust it.
The maths in the post above still applies so 5818 should give you the result you want.

I have the VDO setting instructions, I'll pdf them and pm them to you.

[XTR2Turbo]

Thanks

PDF file would be great. I'll make the changes over the weekend as suggested.

David

[YIIHAA]

I have sent you the scanned copy of the instructions, but they are also here:
http://www.gomog.com/allmorgan/VDOCALIBRATION.html

I used the second method "Manual Calibration with a known value (PULSE)" and Ultima told me to set 6370, which gave perfect results for my setup. I'm guessing your setup has less teeth on the sensor wheel.