147 Speedo Callibration

[Park147]

I have a 2002 Selespeed 147 with 205/50 R16 tyres.
The Speedo is reading about 10% slow - whilst this is safe it annoys me as im not sure exactly what speed i'm doing.
Does any one know if its possible to callibrate the Speedo on these cars? And How?

[Park147]

oops I meant about 10% fast. ie. Speedo says 110 actual speed about 100

[colcol]

Re Speedo calibration, you can buy a kit at Jaycar that can calibrate the speedo, it used to be a tiresome procedure to calibrate the speedo by driving past those 'CHECK SPEED HERE' signs along the freeways, but with a GPS it is a piece of cake, just make sure you can adjust while driving along, then install it out of the way behind the dash out of harms way, Colin.

[Park147]

Thank you colcol ..... I will check this out.

[colcol]

Re 147 speedo, according to my Jaycar book, it is a DIY kit called the  Speedo Corrector Mk2 and you can alter the speedo signal up and down 0%-99% from the original signal, beats speeding fines hopefully.

[pep105]

Park 147 while it would be worth getting your speedo calibarated, I think the issue is your running 205/50 R16 tyres where 147's
run 205/55/ R16. This will affect your speedo due to the reduced rolling diameter of your tyres.

[Steve S]

I have original size tyres and the speedometer is still fast by 6-7%

[colcol]

Re speedo's, for the Australian design rules you may find the speedo accuracy is within the tolerance of how inacurate a speedo can be, we had this debate in Victoria years ago with the money, sorry safety camera's tolerance for overspeeding being less than it was than it was for a speedo on a new car, ie it may say you are not speeding, but the goverment has its hand in your pocket releiving you of your hard earned, try using a GPS, as i am told they are quite accurate, and see if it 5% faster or slower throughout the range or say 5 kph slower or faster throughout the range, you may be able to remove the speedo needle on the speedo shaft and reposition it, i did this once on my 33 after i had installed a new needle due to the fact the sun had bent the original one, Colin.

[Steve S]

After I bought my first GPS about 3 years ago I don't tend to look at the factory speedometers anymore.

[Park147]

So I now have the jaycar speedo corrector.
The corrector works by altering the frequency of pulses to the speedo.
On consulting the wireing diagram in the manual I see that the signal to the speedo comes from the body computer as a multiplexed CAN signal along two wires. I don't think I should cut either of these.
It looks like the next stage back is the speedo signal from the ABS computer to the body computer. Can anyone confirm that this is the insertion point for the corrector? - don't want to cut anything I shouldn't. It seems to me that if this has the correct signal then correcting at this point will also adjust the consumption figures and the distance to go etc on the cars digital readout.

[Park147]

PS. I have a GPS but don't always have the distracting thing on - besides I find it much easier and safer to glance at the car's speedo than read the tiny writing on the GPS screen. Maybe I'm showing my age - I also find it much easier to tell the time from the picture that an analogue clock gives than to read the numbers on a digital display.

[colcol]

I can only refer to my experience with 33's, there are 3 wires going into the speedo, earth, positive and pulse, the pulse wire going into the speedo should be cut, and the wire coming from the gearbox, or in your case the computer, should be cut and the pulse sent to the speedo corrector, and the wire coming out of the speedo corrector to the speedo, if you cut a wire and what you do doesn't work, you can always rejoin it, but don't solder it as you will end up with resitance problems, one of the issues you might have is blowing up a computer in the car if you send the wrong power somewhere, so be aware of this, you might want to take it to a speedo expert in Adelaide, and you are right, driving round looking at a GPS speed is very distracting, the GPS has a large blindspot in the car, the reason why fighter pilots don't like digital instruments is because they look at a digital readout and their brain has to compute what it all means, look at an anolgue dial and you can judge where you are by the position of the needle in the gauge, i can read the clock quicker in my 156 cause it has 2 hands to judge, look at the digital clock in the 33, and my tiny brain has to work out what the numbers mean, Colin.

[Park147]

Thanks for your reply colcol, It would be good if it were as straight forward as the 33. The 147 has a speed sensor on each wheel that send their pulses to the ABS unit that then combines them somehow to produce the discrete signal that then goes to the body computer where its converted to a network digital signal and then on to the speedo in the instrument cluster.
And I think that by reading and re-reading the manual and talking it out that I've answered my own question.

There is now only the matter of the colour code for the particular cable I need to cut. The diagram says the colour of the wire is "BV". Normally I would read this as Black/Violet or Blue/Violet. But as they also have a colour "H" on their diagram It throws everything into doubt and there is no Legend anywhere to be seen. I'm about ready to cut into the loom to see what colours are there and If there is a Black/Violet and no Blue/Violet then the choice will be made.

Glad to see I'm not alone regarding analogue V digital readouts.

[Park147]

Yep I found the black/violet - cut it - hooked up the speedo corrector - bugger! Immobiliser failure! Back to the drawing board!
Any one else have any ideas? I'm about ready to give up.

[colcol]

Make sure you are cutting the correct coloured wire, in the old days Alfas were notorious for wires changing colours in looms due to bad quality control and the dye on wires fading and changing colour, you might have to take it to a speedo specialist in Adelaide, i remember years ago i had speedo dramas with the 33 speedo and when he fixed it, he took me for a drive, stopped, set the odometer and drove 1 kilometer to a kilometer post, and said the speedo was now accurate, and if it wasn't he could adjust the speedo up and down, by something in the speedo or changing some resistors, you may have to go down this path to avoid damaging expensive computers, Colin.