Speedometer problem

[Wolf_Tm250]

Hi All!

On a friend's ST205 is happening something VERY strange...
the speedometer indicates almost half the real speed.

We changed everything... tried 2 speedo gauges, changed the gbox sensor, controlled the plastic gbox wheel... everything is fine, checked or changed new!

But it still shows almost half the real velocity!



Thanks...

[fivebob]

Almost half, or is it about 0.63 of the real speed?

Has it ever read correctly?

[Wolf_Tm250]

Hi Callum!

Almost half, or is it about 0.63 of the real speed?

YES !!!!!!!!!!!!!!!

Has it ever read correctly?

My friend told me it was right years ago...

[fivebob]

Almost half, or is it about 0.63 of the real speed?

YES !!!!!!!!!!!!!!!

Then it seems likely that someone has converted it to MPH. They probably used a divider circuit on the instrument cluster, or inline between the sensor and the cluster.

[Wolf_Tm250]

Hi Callum!

Almost half, or is it about 0.63 of the real speed?

YES !!!!!!!!!!!!!!!

Then it seems likely that someone has converted it to MPH. They probably used a divider circuit on the instrument cluster, or inline between the sensor and the cluster.

Converting to MPH would make the gauge to increase slower ?
End velocity of instruments (kmh or mph) won't be the same velocity ?
I mean 280kph and corresponding value in mph?

Moreover, all was fine till 2 years ago, and suddendly happened this issue without any external action...

I was thinking about a problem in the signal, or a missing/broken wire, or a earth problem...

[fivebob]

Converting to MPH would make the gauge to increase slower ?
End velocity of instruments (kmh or mph) won't be the same velocity ?
I mean 280kph and corresponding value in mph?

Converting to MPH would make the gauge read 100 when the actual speed was 160km/h. It's commonly done on import vehicles in the UK.

Moreover, all was fine till 2 years ago, and suddendly happened this issue without any external action...

Very odd Have you tried changing the cluster or just the speedo?

I was thinking about a problem in the signal, or a missing/broken wire, or a earth problem...

Unlikely, because the signal is square wave digital signal that is converted to analog by the electronics in the cluster.

[fivebob]

Does the odometer register the distance travelled accurately?

[Wolf_Tm250]

Converting to MPH would make the gauge to increase slower ?
End velocity of instruments (kmh or mph) won't be the same velocity ?
I mean 280kph and corresponding value in mph?

Converting to MPH would make the gauge read 100 when the actual speed was 160km/h. It's commonly done on import vehicles in the UK.

Ah ok, understood what you meant!
No, no divider installed...

Moreover, all was fine till 2 years ago, and suddendly happened this issue without any external action...

Very odd Have you tried changing the cluster or just the speedo?[/quote]

Both...

I was thinking about a problem in the signal, or a missing/broken wire, or a earth problem...

Unlikely, because the signal is square wave digital signal that is converted to analog by the electronics in the cluster.

Ok...
so either the sensor (new) is giving abnormal square wave signal, or there is something strange in the analog conversion...

The odometer register less distance accordingly...

Thanks!

[gasman]

if it has been configured to be in MPh you could get one of those speedo corrector kits from jaycar to bump it back up.

[Wolf_Tm250]

if it has been configured to be in MPh you could get one of those speedo corrector kits from jaycar to bump it back up.

I don't think so...
the car is always been in Italy, and always used by the same owner!
And the issue appeared unexpectedly..

It's a real mistery...

Bye

[fivebob]

if it has been configured to be in MPh you could get one of those speedo corrector kits from jaycar to bump it back up.

Don't know if they have JayCar in Italy

[79rolla]

they havent changed tyer size? altho that would need to be signifcant change is size to get that, also hasn't had a gearbox/diff change thats stuffed up the ratios?

[Wolf_Tm250]

they havent changed tyer size? altho that would need to be signifcant change is size to get that

Yes, but it's a homologated measure (within stock +/- 3%).
Moreover the car always had this measure (235/40-17), even when the speedo was ok...

also hasn't had a gearbox/diff change thats stuffed up the ratios?

No... stock ST205 gbox...

Bye

[gasman]

if it has been configured to be in MPh you could get one of those speedo corrector kits from jaycar to bump it back up.

Don't know if they have JayCar in Italy

Oh real? gutted to be living in Italy then .

could always try running a new wire from the sensor to the dash in case its a loose wire or something similar.

[iOnic]

Check resistance of speedo sensor wires and compare to another ST205?

[fivebob]

Check resistance of speedo sensor wires and compare to another ST205?

It's a digital signal, not analog, resistance is futile

[fivebob]

Wolf,

Have you got access to an oscilloscope, or a multimeter with a logic counter?

If so you could compare the output of the speedo drive at the gearbox to the input at the gauge cluster. If there's no difference, and the frequency is the same as your ST205 at the same speed, then the problem must be in the gauge cluster circuit that does the digital to analog conversion.

If the frequencies are the same at the two locations, but different to your ST205 at the same speed, then the problem lies with the speed sensor or the mechanical drive to the sensor.

[matt dunn]

resistance is futile

Checking resistance will however, tell you if there in an intercepter or something in the system.

We had a problem with an MR2 that after a year or so the speedo stopped,
and traced it to a speed Cut defender that the wire had come off, that the customer did not know was there.

It may have had something fitted by a previous owner that has failed,
or has just started working.


Out of interest, on the face does it have written KMH or MPH?
Dont know what they use in Italy?

[iOnic]

Check resistance of speedo sensor wires and compare to another ST205?

It's a digital signal, not analog, resistance is futile

Measuring resistance and comparing to base readings from another ST205 however will confirm if there are devices fitted inline or anomalies in the wiring between the sender and cluster. Once you've ruled that out you can look at the cluster or sender individually even though it's doubtful that either of these are the problem given that multiple replacements haven't resolved the issue.

[Wolf_Tm250]

Check resistance of speedo sensor wires and compare to another ST205?

It's a digital signal, not analog, resistance is futile

Measuring resistance and comparing to base readings from another ST205 however will confirm if there are devices fitted inline or anomalies in the wiring between the sender and cluster.

Yes, I could try this... thanks!