Noisy tach signal from coil negative post

[Razzo rosso]

Hi all

I want to pull a reliable tach signal from somewhere on my Spider, but the recommended coil negative is very noisy, with lots of high-frequency high-voltage (>5V) transients.

Car runs fine with no obvious signs of a failing coil. Haven't checked coil resistances though.

Is this any other source of a reliable tach signal of ~5V.

Thanks
Simon

[Tifosi]

There 'might' be a place to tap into the Motronic, or it may even have a deliberate output that feeds what you need, though of course it has to be a pulsing signal not a steady state voltage output.

Does your current tach spike and weave a lot?

Granted your coil may be a bit noisy, but it's how tachs have been connected for quite some years now with the only other way to do it forever ago being mechanical drive. (which wouldn't work for your monopod anyway)

As an aside, have you checked the coil you have for breakdown or potential failure?

I don't have my hands near the words right now, but there's a couple quick tests you can do with a multimeter that can indicate if there's an issue.

[Razzo rosso]

Hi Tifosi

The mono pod display tach signal is good. I will check the coil, this weekend.
Thanks

Simon

[slyalfa]

the (-) should have more like spikes of 500V as it discahrges. then it will ring and that is normal. if the tach is ment to go to a coil it should be fine. if it is a logic level tach then it needs to be feed off the ecu or the coil amps tach output.

[Razzo rosso]

Hi Sly

What is "the coil amps tach output"?
Thanks

Simon

[slyalfa]

on the Milano there was a hall amp under the coil. I think the spider has the same part some where.
this part was use on a lot of cars like VWs BMWs etc and most have a extra output for the tach.
the Milano did not use this output but had a coil driven tach. but I think the part had the output it just did not go anywhere. I had one go bad and use one off a BMW