electric speedo drive testing

DaveEFI · Post by **DaveEFI** » Wed Sep 28, 2011 8:27 am

I've dug out a spare SD1 speedo and measured it between input and ground. Reads 461 ohms which suggests to me it is supplying the ground for the sensor electronics. So change the resistor value to 470 ohms. (standard value)

With the resistor in place, but no speedo connected, I'd expect to see a reading on a DVM set to AC across the resistor when the sensor is spinning. If you have one which measures frequency, that should vary with the sensor speed.

gelmonkey · Post by **gelmonkey** » Sat Oct 01, 2011 7:25 pm

DaveEFI wrote:I've dug out a spare SD1 speedo and measured it between input and ground. Reads 461 ohms which suggests to me it is supplying the ground for the sensor electronics. So change the resistor value to 470 ohms. (standard value)

With the resistor in place, but no speedo connected, I'd expect to see a reading on a DVM set to AC across the resistor when the sensor is spinning. If you have one which measures frequency, that should vary with the sensor speed.

Hi Dave
You have pretty much lost me with that I'm sorry to say.
The resistor turned up and I have wired it exactly as you have shown and tested it all tonight.
Sorry to say but nothing has changed with still no reading anywhere.
All but ready to throw my toys right out of the pram now

Any more ideas Dave?

I really DO appreciate all of the help that you and the rest of the guys are giving
P

DaveEFI · Post by **DaveEFI** » Sun Oct 02, 2011 6:07 am

Thre is actually 12 volts feeding the sensor?

With the resistor in place and a DVM set to AC you should get a reading of several volts from the sensor when the car's moving.

Just to recap, does an ordinary SD1 speedo work (without the resistor)?

Up early, as I'm off the Billing for the SD1 club spares day...

gelmonkey · Post by **gelmonkey** » Sun Oct 02, 2011 9:11 pm

Hi Dave
Hope you had a good day at Billing and grabbed some bargains.
The problem I have is that the Cavalier wiring loom is not the same as the SD1 loom in lots of different ways and this could well be my problem although nothing is impossible to sort out at the end of the day.
I was gutted last night when I still had the same problem.
I guess if Autometer had a place over hear I would not be reluctant to send the sender and speedo off to have them check things out but to send it back to the US is a pain.
Am open to any other suggestions you may have mate.

cheers
P

minorv8 · Post by **minorv8** » Mon Oct 03, 2011 4:43 am

Just a thought but would it not be possible to use a Hall effect distributor to check whether the problem is the sender, speedo or both. The speedo does not really care what the source of the pulses is.

I don´t remember how the Vauxhall dizzy works but later Lucas with dizzy mounted amplifier could be used. Just drive the dizzy with a cordless drill.

If you suspecet the wiring you should draw separate wires from sender to speedo. The speed signal may be go to the ECU and from there to the speedo ? Maybe something happens along the way ?

gelmonkey · Post by **gelmonkey** » Mon Oct 03, 2011 6:49 am

Am using a Mallory magnetic dizzy if that is any help?
With all this hall wave stuff I am way out of my depth so am basically in everyone else's hands here

Cheers
P

DaveEFI · Post by **DaveEFI** » Mon Oct 03, 2011 7:32 am

gelmonkey wrote:Hi Dave
Hope you had a good day at Billing and grabbed some bargains.
The problem I have is that the Cavalier wiring loom is not the same as the SD1 loom in lots of different ways and this could well be my problem although nothing is impossible to sort out at the end of the day.
I was gutted last night when I still had the same problem.
I guess if Autometer had a place over hear I would not be reluctant to send the sender and speedo off to have them check things out but to send it back to the US is a pain.
Am open to any other suggestions you may have mate.

cheers
P

Can you give a link to a schematic your particular Cavalier loom? I assume you've checked it does provide 12v to the sensor - same as the SD1 does?

DaveEFI · Post by **DaveEFI** » Mon Oct 03, 2011 7:42 am

The two likely types of sensor IMHO for a speedo would be VR (variable reluctance) This generates is own output, so needs no power to it. A hall effect has electronics so requires a 12 volt supply. The only real difference in practice between the two is the hall effect gives a constant level signal regardless of speed - the VR one will give a small one at low speeds rising with speed. But that only applies to the signal level - both will give a varying frequency with speed, which is what allows the speed to be measured.

gelmonkey · Post by **gelmonkey** » Mon Oct 03, 2011 10:21 am

Hi Dave
For the 12v+ supply I have come straight off the back of an igniton fed live to just test things.
The MK1 Cavalier was always a cable operated speedo so no wire to energise a speedodrive was fitted.

cheers

P

DaveEFI · Post by **DaveEFI** » Mon Oct 03, 2011 12:08 pm

gelmonkey wrote:Hi Dave
For the 12v+ supply I have come straight off the back of an igniton fed live to just test things.
The MK1 Cavalier was always a cable operated speedo so no wire to energise a speedodrive was fitted.

cheers

P

A - right. Your comment about the loom confused me.

Can you hook out your DVM set to say 20 volts AC across the resistor - (output to speedo and ground) and see what it reads with the car stopped then moving?

Basically trying to find out if it's the drive or head or wiring that is faulty.