Lotus Elan

Testing a Pos ground tach.

PostPost by: tvacc » Wed Mar 18, 2015 6:39 pm

Testing a Positive ground Tach.

I have an issue that I posted about before. A 66 Elan and the tach is not working. I have hooked up the positive ground and the negative power. The wire that goes from the Ignition switch passes through the tack sensor block and then on to the negative on the coil. Car runs.

I have pulled the tach. A friend of mine that has a business that he repairs industrial controls and can create any kind of pulse I want.

I would like to test the tach before I send it out for repair. Is there anyone that knows if I hook up the pos ground and the neg power, then connect a pulse wire to the sensor lug on the tach, can I get it to register if the tach is OK?

Any other ideas welcome.

Tony
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PostPost by: billwill » Thu Mar 19, 2015 1:05 am

Its difficult to say really, I think the tachos are designed to generate a short fixed width pulse from the leading edge of the coil wave form, becuasue a typical wave form looks like this:

Image

So any pulse of at least 12v with sharp leading edges should do the trick.

You can work out the frequency from the number of spark plugs and the RPM.

4 plugs at 4000RPM = 16,000 ppM equivalen to 16,000/60 cycles per sec = 266.7 hertz.
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