Current Driven Tacho

[grant620]

Hi Guys

I'm installing an ECU on a 1972 Datsun 240Z with a Step 2 RB25DET engine. Interesting job!

Only issue I've got at the moment is the rev counter / tacho.

It is a "4 wire" Tach which senses current from the positive side rather than having a trigger from the coil on the negative side.

I understand that there is some sort of "converter" you can buy to make this sort of Tach work with a proper ECU, but I'm damned if I can find anything!!!!

I'm happy to get the soldering Iron out and make a circuit up, but I'm not a full-on electronics dude, so not sure what's needed...

Any pointers?

[ignitionautosport]

I hate to be that person, but are you sure...? I have a circuit for converting to those using negative coil triggers.
I have never heard of the type you describe. I guess I'm curious and want more info....

EDIT: ok I found a wiring diagram. That is seriously messed up.

[ignitionautosport]

get a 280Z tach. They are a "normal" tach that runs off the negative side of the coil (Source)

Most solutions I saw involved replacing the tach with one that works with the Engine Control Module (ECM) output, or attempting to convert the 240Z tach to accept the ECM output. While this all works, it is unnecessary, and assumes the only way to get a tach signal is to work with the ECM output.

The other way is to supply the six ignition coils via the standard 240Z coil supply.(Source)

May be helpful.
I really should go price some stuff for a customer instead of looking up weird shite on the intertubes lol.

[stevieturbo]

So how are these things wired and work ?

[ignitionautosport]

http://images.lmgtfy.com/?q=240Z+tacho+wiring

In short, very oddly.

[stevieturbo]

So what happens if you just leave it wired the same way ?