Speedo Help please...
Discussion
Hi,
My speedo has recently packed up on me
I have had the sensor replaced to no avail and have just had the actual speedo tested at speedy cables, who inform me it works fine
I get no reading at all, unless at speed in which case it sometimes flickers, and the odometer does not work.
Apparently the only way speedy cables could get the same thing was to drop the voltage supply down below 10.5 volts. They have suggested that it is probably an earting problem.
Has anyone had a similar problem? and if so whats the next step? Does the signal to the speedo come direct from the sensor or from the ECU?
ANY help much appreciated.
My speedo has recently packed up on me
I have had the sensor replaced to no avail and have just had the actual speedo tested at speedy cables, who inform me it works fine
I get no reading at all, unless at speed in which case it sometimes flickers, and the odometer does not work.
Apparently the only way speedy cables could get the same thing was to drop the voltage supply down below 10.5 volts. They have suggested that it is probably an earting problem.
Has anyone had a similar problem? and if so whats the next step? Does the signal to the speedo come direct from the sensor or from the ECU?
ANY help much appreciated.
If it has the later box,( reverse to the right and back I think) then the speedo will get its signal from a sensor mounted either near the prop shaft or around the diff.
Having read quite a few posts on here it seems this has to be set quite closely to get it to switch.
I checked my signal (albeit on the rover box with built in transducer) by using a voltmeter.
If you jack the car up , just one side, and measure the signal wire where it arrives at the speedo .
You should see the voltage switch slightly as you turn the jacked up wheel.
Many people say use an oscilloscope, but to just see it switch then a voltmeter will do.
The oscilloscope will help to see the pulse at a higher frequency.
Hope this helps and of course it is covered in detail in the bible
Having read quite a few posts on here it seems this has to be set quite closely to get it to switch.
I checked my signal (albeit on the rover box with built in transducer) by using a voltmeter.
If you jack the car up , just one side, and measure the signal wire where it arrives at the speedo .
You should see the voltage switch slightly as you turn the jacked up wheel.
Many people say use an oscilloscope, but to just see it switch then a voltmeter will do.
The oscilloscope will help to see the pulse at a higher frequency.
Hope this helps and of course it is covered in detail in the bible
Give us a bit more of a clue to work on. Is the sensor on the diff or the gearbox ( or in other words which gearbox do you have ? (where is reverse gear) As well as driving the speedo, the ECU uses the speed sensor to adjust the idle. When you come to a halt the engine revs will initially be fairly high and then after a few seconds drop down to a lower level. ( This is assuming the engine is warm and the stepper motor is working) If your car does this then I would guess that the speed sensor is working and the signal is getting to the ECU.
Thanks for the replies,
Final got time this week to have another quick look.
The reverse gear is right and back and the sensor has been replaced at my service (since this is what I though was wrong). Anyway the speedo is getting a 13v supply, so I guess the only thing is the feed from the sensor is not getting through.
Steve - to answer your question, the car is running as normal, i.e on stopping the revs drop down after a few seconds and the car is idling fine, so I guess the signal is getting to the ECU.
Assuming the signal is at the ECU but not the speedo, whats next? or am I looking at a return vist to the garage!
Thanks for any suggestions....
Final got time this week to have another quick look.
The reverse gear is right and back and the sensor has been replaced at my service (since this is what I though was wrong). Anyway the speedo is getting a 13v supply, so I guess the only thing is the feed from the sensor is not getting through.
Steve - to answer your question, the car is running as normal, i.e on stopping the revs drop down after a few seconds and the car is idling fine, so I guess the signal is getting to the ECU.
Assuming the signal is at the ECU but not the speedo, whats next? or am I looking at a return vist to the garage!
Thanks for any suggestions....
As the ECU is obviously getting the message and you say the Speedo has been tested the I guess the pulses are getting to one and not the other. My V8s suffered from a “lazy” Speedo if the car had not been used for a few weeks, after a mile or so it always came to life. I understand that there was an “amplifier” somewhere that boosted the Speedo drive pulses. Sorry not a lot of help I know, will take a look at the circuits tonight to see if there is any thing obvious.
I experienced the same problem on my Griff 400.
I replaced the sensor, but only got some kind of a (temporary) readings at speeds above 120 kph.
The solution for me was to adjust the sensor closer to the toothed wheel at the diff, really as close as possible. This means: just not touching it, so less than 1mm gap!!
BTW: check also if your toothed wheel is not out of balance meaning it has a tooth 'out of the circle', this would prevent hitting the sensor at the first full turn.
Good luck, Ben
I replaced the sensor, but only got some kind of a (temporary) readings at speeds above 120 kph.
The solution for me was to adjust the sensor closer to the toothed wheel at the diff, really as close as possible. This means: just not touching it, so less than 1mm gap!!
BTW: check also if your toothed wheel is not out of balance meaning it has a tooth 'out of the circle', this would prevent hitting the sensor at the first full turn.
Good luck, Ben
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