My tacho likes to read from 0-3000 and no more!!! When the needle reaches 3000 it stops...falls down...then it pops back up to 3000 when the engine starts running down past 3000rpm and follows it down to zero again...WTF?

I have zetec with edis and smiths tacho...any ideas?

Is the feed wire shielded ?

If not that may help, although only earth one end.

Rgds Mark

Its not like its twitching, it just seems to stop at the same place everytime??? Strange...

a million things could be the problem, but yours sounds like the tacho might benefit from a bigger signal - if you're feeding it from a 'logic' signal from ECU it might be 5V instead of 12, or not beefy enough. If you're taking the signal from the coil LT you might have tapped off the ballast resistor side of the coil instead of the switchy side???
Point is I guess the smiths tacho is engineered to read coil LT type voltage, so the input is heavily filtered. SO when the frequency goes up, the filtering makes the signal too small to detect.
Good luck - no doubt you'll find it's nothing to do with any of the above.......
Bob

Do you have diodes connected to the EDIS coil as per this thread ? (make sure you read the thread though!) http://www.locostbuilders.co.uk/viewthread.php?tid=47440

If you are using Megajolt , that is a common problem on older tacho's , you may have to connect to the coil leads with resistor / diode network , that 's what I had to do with my old Skoda tacho.

OMG (baffled look)!! Sorry i'm not an electrician, that thread is v.difficult to follow MikeRJ.

The tacho i'm using is new. hmm. Thanks for your help guys i'll have to look into this alot closer.

You basicaly need two 1N4004s or better (e.g. 1N4005, 1N4006, 1N4007) and a zener diode of around 12-15volts. All parts available at Maplins or RS Components or Farnell, or even Ebay.


Adapter to drive tachometer from wasted spark system (e.g. EDIS)

Actual layout of components, note the location of the stripes on the component bodies!

Layout of components

Hope that helps.

That didn't work on mine I had to fit a resistor from the join of the diodes to earth , I think Paulf knows what value , 220 or 220k ohm rings a bell.

1K did the job on mine , anything that pulls it down to earth without drawing to large a current will do.
Paul.

quote:

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Originally posted by Surrey Dave
That didn't work on mine I had to fit a resistor from the join of the diodes to earth , I think Paulf knows what value , 220 or 220k ohm rings a bell.

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The answer is here:

http://www.locostbuilders.co.uk/viewthread.php?tid=29956&page=1

Good work. Cheers

quote:

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Originally posted by Chaz
Good work. Cheers

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