S3 speedo very inaccurate

[The Horse]

Hello
Just returned from Wentworth Woodhouse and a big thank you to the organisers. A great day out despite the dull (but thankfully dry whilst we were there) weather. 330 miles with the top off and great fun.
This was this first "proper" drive I've had in my S3 which I bought a couple of weeks ago and I've noticed two problems.
The headlights are truly dreadful and it seems as it the dim/dip is stuck on dip...but I'll look for help in another thread.
The other problem is that the speedo is really really inaccurate.
I had SatNav stuck on the windscreen and at just below 3,000 revs in 5th gear the SatNav was showing 70mph but the speedo was showing 95mph !!
The speedo seems to consistently over-read by 35% throughout the speed range.
SatNav 60mph was at 2,500 revs and SatNav 50mph was at approximately 2,000 revs.
Do these sort of engine speeds versus road speeds seem accurate ?
Is the speedo mechanical or electronic ?
Has anyone else had a similar issue and any ideas how to solve it ?
Thanks
David

[phillpot]

The Horse said:

Do these sort of engine speeds versus road speeds seem accurate ?

No, not even for a TVR.

The Horse said:

Is the speedo mechanical or electronic ?

Early cars were mechanical (cable) but your S3 should be electronic.

The Horse said:

any ideas how to solve it ?

Sorry, no

[The Horse]

Hello Phillpot
What I meant about road speed v engine revs accuracy is should I expect roughly 24mph per 1,000 revs in 5th gear which is what the tacho and SatNav are suggesting ?

[phillpot]

Do you have the Steve Heath book?

There is a gear ratio guide, 5th gear should be 147.6 mph @ 6000 revs ( theoretical )

so your sat nav figures are pretty accurate.


Shouldn't make a huge difference but are you on standard size tyres, 205 60 15's ?

[The Horse]

Yes standard tyres, at 22 psi all round.

[cheddar]

The Horse said:

Yes standard tyres, at 22 psi all round.

Sausage fingers typing or prefer a pillowy ride?

[The Horse]

i thought 22psi was the correct pressure ?
That's what the TVR handbook states......

On the basis the revs to road speed indicated by the SatNav are reasonable, the problem must either be in the gearbox sender or the speedo head or in the wiring in between.
Does anyone have experience of faults in any of these ?
David

Edited by The Horse on Sunday 1st October 21:46

[v8s4me]

Tyre pressure would not lead to a 35% error. One possibility might be that at some time either the speedo or the sender have been replaced and they are not matched. If that were to be the case then you'd need to send both off to be calibrated. Speedy Cables is one company which can probably do this but they are very slow. JDO Instruments got a good mention on here back in July.

[jwigglesworth]

Your revs/ satnav speeds correspond to those on my S2.
Had to have my speedo redone at Speedy Cables who turned out to be anything but (nearly 6 months!) and up to 60-ish MPH the speedo is accurate to the satnav. Above that it loses interest t the point where an indicated 75 is 85 on the satnav!
Not too bothered by this as I use the rev counter more than the speedo anyway for judging speed.
No idea how to solve your problem as my diy skills stop at changing a lightbulb!

[GreenV8S]

The Horse said:

i thought 22psi was the correct pressure ?

Seems about right to me.

[phillpot]

cheddar said:

Sausage fingers typing or prefer a pillowy ride?

What pressures do you run?

[Jed-S]

When I had a S3 my speed used to increase noticeable by turning on the lights and the heater fan. The culprit was the infamous yellow connector.

[cheddar]

phillpot said:

cheddar said:

Sausage fingers typing or prefer a pillowy ride?

What pressures do you run?

Sorry op, I misunderstood the thread and was was wrong, dug a hole deep enough to not climb out of, please carry on without me

[DamianS3]

Jed-S said:

When I had a S3 my speed used to increase noticeable by turning on the lights and the heater fan. The culprit was the infamous yellow connector.

Yup I used to gain 20mph by putting the lights on.. rebuilt speedo and chin sensor fixed it for me. FYI I am not running the type 9 hence need for chim sensor.

I have also tidied up the headlight wiring which was probably the cause. My yellow connector is long gone

Damian S3

[The Horse]

What is the "yellow connector" being replaced with ?
Cheers
David

[GreenV8S]

The Horse said:

What is the "yellow connector" being replaced with ?

Usually a direct splice connection. You can use a high current connector if you anticipate needing to remove the steering column frequently.

[v8s4me]

I replaced mine with an Anderson Connector. Well over the top but does the job.

[GreenV8S]

It needs to handle somewhere in the region of 20-30 Amps. You could use something much smaller than an Anderson connector but there's no shortage of space around there and the Anderson seems like a reasonable choice.

[phillpot]

GreenV8S said:

You could use something much smaller than an Anderson connector

Like some Mini Anderson connectors


whatever you use it all depends on how well you can crimp or solder the connections, unless.............

[The Horse]

I have yet to tackle the "yellow connector" but in the meantime, whilst having the centre console out I've had these washers made out of 2mm stainless which enable me to easily get an earthing point through the two body / chassis M10 mounting bolts found under the centre console (using a 6mm eyelet connector bolted to the washer)
Hopefully once I've tapped into the instrument earthing circuit it will help the reliability of the car's electrical earths.
In hindsight, 2mm is over-kill and 1mm would have been fine

Edited by The Horse on Thursday 19th October 11:43