33 replies to this topic

[westlin]

I have a smiths rvc rev counter fitted to my son's 1275. Ive changed the ignition to a power spark distributor. The issue I have is one minute its accurate the next it bouncing all over the shop. I saw someone add a resistor in the feed 10k, whic I have done but has made no difference.

Any suggestions

[westlin]

I have a smiths rvc rev counter fitted to my son's 1275. Ive changed the ignition to a power spark distributor. The issue I have is one minute its accurate the next it bouncing all over the shop. I saw someone add a resistor in the feed 10k, whic I have done but has made no difference.

Any suggestions

[Magneto]

Sounds like a loose connection to me, double check your wiring....especially at the coil.

[westlin]

Ive just checked the connection from the dist to the coil and ive connected the black wire to the white and black and the other end to the coil. Should I eliminate that link as well.

could see any loose wires though

[leadly]

Ignore me, didn't properly read what you had written.

Edited by leadly, 13 March 2016 - 06:14 PM.

[David128]

feed and signal on correct connections?

[Moggyton]

Could be a dodgy earth somewhere? I fixed my bouncy rev gauge by grinding some paint off the battery earth in the boot :)

[slidehammer]

I had a similar problem the gauge would be fine on start up and after a short while start bouncing around like a windscreen wiper. It turned out to be where I had taken the switched live from - it didn't like the voltage stabilizer for the fuel and temp gauges. I moved to a normal unstabilized supply and it was fine.

[dklawson]

... ive connected the black wire to the white and black

and the other end to the coil. 

 

You said this is an RVC type tach.  There are several types.  Some have wires some have terminals.  What did you install?  Can you post a picture?

 

 

The picture below is from an MG web site and shows the wiring on back of an RVI tach.  

Note the green wire.  That is switched 12V power in.

The white wire with the stripe goes to coil (-).  (Should be white/black not white/blue)

The black wire is connected to the gauge case for an earth.

The red wire is for illumination.

 

Note there is only one connection to the coil.

 

[westlin]

Can't get a picture tonight but it has 3 terminals signal, power and earth. Signal is the white and black wire from coil, power is light green and orange and earth

[westlin]

Ive checked the wiring tonight. No loose conections, good continuity between the white/black wire from under the bonnet to the dash. Earth is good and the 12v supply is good as well.

any other suggestions?

[dklawson]

The RVC tach senses voltage pulses on the coil's low tension circuit.  There can be large spikes on the low tension wiring and that is probably why some people try adding the resistor you experimented with.  Getting a resistor or a combination of a resistor and capacitor to fix the problem will be rather hit-and-miss.  I would pursue other options first before trying to filter out noise.

 

I have a few suggestions.  None may seem attractive at first.

If you have a set of points and condenser, fit them to the distributor instead of the electronic module.  If the tach behaves properly with points, there may be an issue with the electronic module.  If the tach still misbehaves with points, BORROW a different ignition coil for your car and try again.  Only buy a new coil if the borrowed one makes the tach behave.

Finally, if none of these things highlight the problem, see if you can find a friend whose car you can try the tach in.  If the tach fails to work in the other car, send the tach in for reconditioning or buy a similar replacement.

[westlin]

I have the original dash gauges so am go to try that tonight at least that should rile out the gauge.

I'll keep u posted

[westlin]

Could my issue be ballast resistor. I have 2 wires on the positive side of the coil white/ yellow and white/pink where would the resistor be and could this be an issue and how do I check

[cal844]

Could my issue be ballast resistor. I have 2 wires on the positive side of the coil white/ yellow and white/pink where would the resistor be and could this be an issue and how do I check

The white pink wire is the resistor!