Tacho flicking about erratically

I was driving today and my tacho started to randomly flicker - any suggestions what would cause this and where to start looking?


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Problem with coil or coil connection?

 

Something has changed but it might just be aging of components. If it is a VDO you might need the diode as connecting the negative side of the coil to a long wire to the front of the bus can cause problems with "ringing" which can increase the apparent RPM suddenly.

 

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So the rev counter is still driving me made - I have fitted a new coil and no change - not sure what else to change/test


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Bin the rev counter ...

 

Hopefully you can see the needle flicking about like mad - stable for a bit - it seems to be more when I accelerate - the engine sings away as normal -


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If you fit a diode in the wire from the coil .. need to look up which way round it goes, it stops the normal 'ringing'in the ignition circuit that is part of the normal operation from sometimes counting twice..
It could be a change in a spark plug or an earth somewhere or if you have a condenser it may have started to fail..

My home made rev counter needed an electronic filter and changes to its software as it would jump from 1000rpm to 100000rpm aa it measured each cycle of the Kettering ringing as a separate spark plug firing pulse...

 

It worked fine for about 2 months when first fitted - engine is new - so spark plugs one year old - I have already changed the coil to see if this solved it - no change - it is also intermittent - sometimes stable as anything - seems worse when everything is hot


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Mine did this it was simply a poor spade connection to the coil

 

i also fitted a diode to stop the needle bouncing on mine.
I have some spare diodes somewhere if you want to try one.............

 

I had a similar problem after I fitted the diode and it turned out to be my points were on the way out, when I fixed them all things returned to normal

 

The van is running an electronic ignition so hopefully not this


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I will give this a go tonight and replace the spade connector to see what happens


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Thanks for the offer I will just order some on eBay save you any hassle sealing them out!


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To ease fitting I put a crimp male spade on one end and a female on the other and then popped some heatshrink over it

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i did the same, just looks like an extra bit of wire