Wrong tachometer reading

[Peter924]

I've a tachometer for an electronic ignition.
It worked perfect until a few weeks ago.
The dial currently indicates about half the real rpm. It indicates for instance 400rpm at idle instead of 750rpm.
I've chequed the connections, the voltage and the earth wire but could not find the cause of the problem.
Are there any other suggestions for solving this problem ?

Peter

[mallardstag]

Do you have an early (RVI) tacho or the later RVC type?

Running an RVI tacho with electronic ignition can be problematic and updating the innards to the later type would usually cure this.

Simon.

[DZP]

Hi Peter,
When I purchased my MK I Stag it had electronic ignition, with the ignition feed fed through the tacho (as usual for MK I), but no dropper resistor, so the 6v coil was always running at 12v.
It has a Mk II tacho fitted, which was working correctly.
The Ignition feed (white cable) was melting in multiple areas of the loom.
I rewired to take the ignition feed directly to the coil (via a dropper resistor) and the tacho feeding directly from the -ve side of the coil (as per MK II).
I have also replaced the complete wiring loom.
So, if you have a Mk I, then I would check you have a MK II tacho (as detailed by Simon) and that the tacho wiring is also configured as per MK II.
Den

[Peter924]

Thanks for the responses,

This tachometer was supplied the Gauge Shop and is an adapted for electronic ignition version of a RVI for a MkI
The tachometer I had before did not work properly, so I ordered a new one years ago.
It worked well for 5 years.
All wires are in good condition and connected in accordance with the scheme supplied by the Gauge Shop.
The problem is that it has worked well for years and it recently gives a false reading.
I've also contacted the gauge shop and haven't got a response yet.

Peter

[mallardstag]

Thanks for the responses,

This tachometer was supplied the Gauge Shop and is an adapted for electronic ignition version of a RVI for a MkI
The tachometer I had before did not work properly, so I ordered a new one years ago.
It worked well for 5 years.
All wires are in good condition and connected in accordance with the scheme supplied by the Gauge Shop.
The problem is that it has worked well for years and it recently gives a false reading.
I've also contacted the gauge shop and haven't got a response yet.

Peter

If your tacho has worked well in the past and is now reading steadily at about half rpm then it's probably a failure of the electronics inside the tacho itself. If it's jumping about then it's more likely a wiring fault (poor connection/intermittent contact).

As it has been modified internally then it would need to be tested/repaired by the supplier (gauge shop) unless you have detailed info about the modification that was done (circiut diagram etc.).

[Hughesy]

If no luck with the current supplier these work well and the support is great.

https://www.spiyda.com/smiths-rvi-rv...ion-board.html

[Peter924]

If no luck with the current supplier these work well and the support is great.

https://www.spiyda.com/smiths-rvi-rv...ion-board.html

I've had contact with Alan from the Gauge Shop and he also suggested an internal problem.

[flying farmer]

The Stag rev counter in my V8 Toledo has just started doing the same thing. I bought a second had one from Beaulieu yesterday which I hope will solve the problem.