Xanita estate Mk2 1.9td Speedo issues

[John Plum]

So, given a speedo that reads accurately enough, but (often) intermittently cuts out altogether to read zero and, very occasionally appears to stick at about 50 mph and, the tachometer always behaves well ( just like my Xantia actually),

Does this indicate a fault at the speedo clock head itself?
I infer tachometer and speedo share same sensor from statements above.


Sent from a mobile transmitter.

[citroenxm]

No speedo and rev counters use DIFFERENT sensors John. .. speedo sensor is on the gearbox differential and depending on age rev counter on top of the gearbox from the fly wheel sensor..

[John Plum]

Ah, that I need to know Paul, thanks.
Of course, how can a tachometer read from the diff.
So, I should check the sensor first, I think.


Sent from a mobile transmitter.

[RichardW]

That's a fault in the instrument panel, John - there are small spring contacts that transfer the signal off the PCB to the speedo head - a bit of corrosion or loss of spring, and the contact is erratic, and hence the speedo too. There's a post somewhere with pics of dismantling a MK2 panel showing the contacts - it's a bit more difficult than a MK1 where the pins were on the back and just needed re-soldering.

[RichardW]

Here's one, not the one I was thinking of, which has pictures by Jim... http://www.frenchcarforum.co.uk/forum/v ... =3&t=40038" onclick="window.open(this.href);return false;

[John Plum]

Thanks Richard, excellent guidance which helps me no end!


Sent from a mobile transmitter.

[longgo]

Because now i try to build one fuel trip computer for my xantia here is one hint: that VSS sensor send straight the signal to the dash.

The sensor itself has 8 pulses per 1 rpm. So, for my car i need to have standard 185/65/15 tyres. From the service site i got that my tacho have 22 teeth gear on the shaft and 18 teeth gear on sensor axis. That make 22:18 -> 1.222 : 1 gear ratio. So lets get fun, tire 185/65/15 has -> 185*0.65*2*(25.4*15) -> 0.6215m diameter or that is let`s say ideal circle.

0.6215 *3.1416 -> 1.953m of distance for 1 wheel rotation. 1.953m/1.222 -> 1.5982m for 1 sensor rotation or 1.5982m/8 pulses per 1 turn -> 0.1998 m for one pulse.
I guess is added in car dash 0.2m/per pulse because is given 1km as 5000pulses ..(or about). If i get my tire under load to give me 1.9m distance for one rotation then 1.9/1.222 => 1.5548 -> 1.555m measured for one sensor rotation , 1.555/8 -> 0.19438m per one pulse. Or if i get 1 pulse per second
then i have 0.19438*3.6 -> 0.699768 -> 0.6998km/h ...

So now just measure your signal. Lets say, you lift the car from one side, rung the engine on gear and check the signal on cable 162B(blue plug behind dash), or rotate with outside source the wheel and open take off the ecu plug and there on the vss pin check the signal.
Same time you can see what your dash show. If you get 100Hz signal then -> 100hz pulses * 0.6998 -> about 70km/h.. try with other numbers on that logic.

And do not trust so much on the GPS for right speed.
I check my car few times on that outside city radar dash. That is some electronic board showing your current speed. 85km/h on dash - 79 on that board. One time 84 on GPS, one time 80, one time 78... With that logic up uploaded in arduino with lcd 80km .. and i saw that over 65km/h the dash start to show much different.. Also tire size, pressure and so on..

[John Plum]

Sounds about right to me Longgo


Sent from a mobile transmitter.

[falling-out-with-my-car]

Ok it is definitely over reading by 10 mph it passed the MOT fine and I removed my new used Driving school approved heads up speedo in case someone noticed a problem, I know its probably best in the long run to get the speedo fixed properly but my Xantia has spent more than four months in 2013 in a garage having the matrix fitted and then having the engine rebuilt then it had to go back again because the injectors fitted from the spare engine I bought from Xac were seized making it knock and run like a pig when cold that is if you could get it started, its all running sweetly now with my old injectors fitted to the new head and I have a special slot to check the condition of the cambelt through now.

its even doing more to the gallon than it did before and the engine is much quieter to, just want to be able to keep hold of the car and drive it for a bit running around in the 2cv isn't the most comfortable of ways to get around when you are six foot six tall.
for now the He-Man Heads Up GPS display electronic speedo is brilliant and it projects on the screen in the right hand bottom corner it has an alarm for three different speeds I have set it for 30mph 40mph and 70mph you can switch off the alarm if you wish.
I haven't taken my eye of the road since I bought it I have checked it with the local lamppost mounted 30mph speed sign and it is currently set to minus 2mph below 30mph or 28mph when it displays 30mph,, so for now I'm happy with my new toy. maybe when the weather is warmer I'll get around to sorting the speedo out. I have noticed a massively shortened journey time on several trips out and about I can safely and legally drive 8mph faster now.

can anyone confirm whether or not the digital display in the bottom of the S2 speedo remembers the mileage please or do I need to have a replacement speedo programmed with my current mileage?

cheers.

Nigel.

[citroenxm]

It sure does keep the milage.. It has to. Only other thing it can do is count up like the c5.

So. No panic. The milage will still show the same as before.