4 coils tacho

[rx3ip]

hi guys
does anyone know how to connect a tacho if you have 4 seperate coils ( 3sge ) ?
i don't want it to conncect it to the motec cheers

[AndyTTR]

Are you using an ignitor module? Sometimes they have a tacho output.

[takai]

There is a tacho booster which you can make to trigger a tacho, but i cant find the diagram now.
Let me find it when im at home and not in just a textbased browser.

[rx3ip]

what is an ignitor module ?
my engine set up has trigger sensor from the crankshaft and sensor from the inlet cam

[LeeRoy]

They are just for a revolutionary reference for the computer allowing it to know where it is in the firing cycle. Ignitor module holds electricity for coils which charge then spark through the plugs.

[rx3ip]

thanks takai
i have a tacho shift light set up by the motec , but need a second tacho so i can adjust it myself to what ever rev that i need

[rx3ip]

hi leeroy
there are 4 of those that connected directly to the 4 coils

[timbosaurus]

This thread has some useful info...
http://www.toymods.net/forums/showth...ht=diode+tacho

Sounds like you just need to connect a wire to each coil -ve, run each wire into the "stripey" end of a standard diode (1N4004) and connect the other ends together and send it to the tacho. This is assuming you have an early tacho which relies on the voltage spike generated on the coil.

[Hen]

Assuming your dash tacho is an old style one which needs a voltage spike to make it work, the following circuit will do. I've used it with twin coils and it should work with four.

I can't take full credit, it has been adapted from a twin coil Haltech diagram.



Hen

PS, I like Imageshack.us and my paint ski11z are above reproach

[rx3ip]

thanks guys
i will try it

[timbosaurus]

hmmm... was thinking more like so...




But i haven't tried it. Hen's might be better.

Hen, the circuit above grounds the tacho when the (assuming old school engine) points close, but wont let the inductive spike that occurs upon opening through to the tacho.

Your circuit will let a narrow pulse of anything above 15v into the tacho. Is this how you anticipate it to work?

actually, a bit O/T. does anyone know if old tachos count rising edges? count the high voltage spikes? falling edges? Duty cycle of the low pulse (which means changing dwell affects tacho reading... wouldn't think so)?

[timbosaurus]

PS, I like Imageshack.us and my paint ski11z are above reproach

i was an imageshack virgin... it was easy! yeehaa!

and i too would like a job as an MSpaint artiste!

[rx3ip]

timbosaurus
it sounds very complicated , i'm not very good at this thing & needs diagram that very simple , so i can understand it

[LeeRoy]

Wouldn't you only have one ignitor module? I haven't heard of more than one ignitor. Multiple coils i've heard of. Try searching the old forums for what people with sprinters have done as they encounter the same problem when running gze motors as the sprinter tachos run from one coil and the gze motor uses 2 coils so it plays with the rpm.

i'm pretty sure all the parts they need can be purchased at jaycar. If your getting 4 pulses and need only one couldn't you just run the tacho signal from 1 coil not 4?

- Leeroy

[timbosaurus]

AFAIK you need one ignitor per coil. The ignitor takes the small signal from the ECU and takes care of switching current on through the coil, limiting current through the coil, sometimes adjusting the on time (dwell) and switching off sharply to produce the high-voltage spike.

If your getting 4 pulses and need only one couldn't you just run the tacho signal from 1 coil not 4?

You actually have a quarter of the amount of "sparks" per coil in a four coil setup as you do in a single coil. So if you setup as you described, you would read a 1/4 of the actual revs. To get the tacho reading correctly involves connecting one up and multiplying the pulse frequency by four, or simply connect all four up to the tacho... which is a frickload easier! The reason for the diode is so that you dont ground all four coil negative inputs (effectively *switching* all four on) at once.