Tacho Drops To Zero

[ti]

Hi Everyone

I have got a 'new' problem, after fitting a msd 6 series ignition unit about 6 months ago i have now got a tacho that drops to zero when i acclerate this has only just started to do this - any ideas ???????????

[wilf]

Yup - your tacho needs some capacitors fitting to cope with the square wave output of the MSD.

Nope - I don't know how much capacitance or where to fit it - I sent my tacho back to Speedy Cables to modify. Maybe an electronics whiz here can give home-fitting guidance.

[ti]

Thanks for your reply Wilf

I dont know if this applies as i have not used the tachometer output terminal on the side of the msd ?!?

[Alex Miller]

I think you can get a simple adaptor from MSD that will sort out the signal for your tacho.

[kurrmet]

I think this may help a little.



http://autos.ninebean.com/cobraclub/...ighlight=diode

[wilf]

Terry - I think you should use teh MSD tacho output - the main output to the coil might be a bit fierce for your tacho, plus of course an MSD sparks 3 times per "go" below 3000 rpm, that is why the tacho output is there.

Iain - I had forgotten about the diodes! Anyone care to advance a theory as to how/why they work? (not the diode, but the practice of putting one into the line to the tacho).

[Clarkson]

I had this problem not that long ago with my MSD unit,the tach adaptor did not work for me!

I spoke to speedy cables and there is a mod,but you have to send in your tacho and pay £50+ vat! I was better of buying a new smiths tacho.

You must use the tacho output on the MSD box and NEVER add any extra wires to the coil +or- as it runs at 500volts!

[ti]

Thanks Guys

I will look into your suggestions

[snakebite]

Connected my tacho to the tacho terminal on the msd unit and worked fine?

[Purple AK]

Originally Posted by snakebite

Connected my tacho to the tacho terminal on the msd unit and worked fine?

Ditto