How does the speedo work on a GT3?

[910Esprit]

Currently looking at an intermittent speedo on a GT3. (presumably the same on all later models) I assume its electrical? (unlike my mechanical jobbie) If so, where does it get the signal from (ECU?) What tells the car what gear its in? I'm assuming its just a bad connection somewhere, but am just looking for pointers.

Cheers

[ramjet]

Silly answer:

As you go faster, the needle rotates to the right across a range of number. It's the same on all esprits. Unless someone has fitted a digital speedo.

Serious answer:

As far as I know, any electrical impulse speedo has to get its signal from the final drive side of the gearbox. Nothing else will work consistently.

[jonwat]

What tells the car what gear its in?

Nothing.

[sailorbob]

The Sport 300 speedometer gets its input from the ecu and the other models pre January 1995 were mechanical. I'm not sure about January 1995 onwards as the speedometer was changed but I don't know if it became electronic too.

[s4simon]

Freescan will sort the problem out.

Another check to do is recalibrate the speedo. My VDO speedo is set to 4000 pulses per KM.

[ramjet]

How does the ecu signal work Derek?

[sailorbob]

It's pin B8 and available on all ecu's, 4000 pulses per mile I believe.

[910Esprit]

Hmmm interesting, so how does the ECU know what gear the car is in?

[Mr_John111]

Does the ECU take a reading from the ABS sensors on the hubs?

If so then it is academic as to what gear it's in as you can calculate road speed from the number of revolutions the wheel makes and the known circumference of the tyre

John

Edited April 11, 2012 by Mr_John111

[braziers]

correct me if im wrong i think the speedo picks up the pulse of the front wheel abs sensor. ecu knows what gear your in as it calculates revs vs speed. thats as i understood it.

[sailorbob]

The ecu speed sensor is in the right hand rear hub carrier. The 4 cylinder ecu's do not infer gear and don't know the gear you are in.

[ramjet]

So I was right. Signal comes from the final drive.