Megasquirt Support Forum (MSEXTRA)

Hi all,
I've "upgraded" my ignition system to 4 individual cop's and ditched the Ford Edis Module after it was giving me some headaches.. 2 cylinders were dying and the cause was a dying igniter inside the module, i replaced several modules and was getting the same problem everytime... Dwell time was 2.3 ms
So I used 4 D585 GM coils , work great with no issues at all so far
I previously made the tacho work with the Ford Edis coil tower by using a tach adapter (picture attached), and now that I have the "Tacho" output from the MS3X, I tried to make it work (without the tach adapter, lost it) but it does not;
The tacho is from a 86 Model Year Nissan Silvia S12 triggered by the negative side from the coil (Distributor Equipped Engine)
I tried to trigger it by the Pin 36 from the MS3 Bosch BIP373 JS10 but it didn't work either
Attached are pictures of the Tacho

Any help very much appreciated

Nissan S12 Tacho

A tach fed from a coil negative (or from several coil negatives as with EDIS) expects to see a pulse of about 40volts. The pulse from an MS processor is about 5v. If you wish to run that tach from this 5v signal, you need to add a circuit to generate a 40v pulse from it. Common way is to use a single transistor driving a standard auto relay coil. The coil acts like an ignition coil, and produces a large flyback pulse. You''l find full details in the manual linked to above. I think you may also be able to buy one ready made.

DaveEFI wrote:A tach fed from a coil negative (or from several coil negatives as with EDIS) expects to see a pulse of about 40volts. The pulse from an MS processor is about 5v. If you wish to run that tach from this 5v signal, you need to add a circuit to generate a 40v pulse from it. Common way is to use a single transistor driving a standard auto relay coil. The coil acts like an ignition coil, and produces a large flyback pulse. You''l find full details in the manual linked to above. I think you may also be able to buy one ready made.

Thanks Dave,
Can you post a link to that adapter ? Any ones you're familiar with or advise me to buy ?

DaveEFI wrote:A tach fed from a coil negative (or from several coil negatives as with EDIS) expects to see a pulse of about 40volts. The pulse from an MS processor is about 5v. If you wish to run that tach from this 5v signal, you need to add a circuit to generate a 40v pulse from it. Common way is to use a single transistor driving a standard auto relay coil. The coil acts like an ignition coil, and produces a large flyback pulse. You''l find full details in the manual linked to above. I think you may also be able to buy one ready made.

Can I also use JS10 Output from Pin 36 from the mainboard as the transistor ?