Tach signal from COPs

[Jan Pedersen]

The 1ZZFE coils I am using have a tach output but what kind of signal do they put out? I tried using a oscilloscope connected to ground but I got no signal. I did not try with the scope connected to 12 V or by using a pull up resistor and this will be next if I can't find a certain answer.

[Jeonsah]

I know its not much help but a COP tach signal output should only ever be 0v or a 12v depending on if the COP has fired or not. So the varying frequency (pulse width modulation) of the COP signal firing is what the output of the COP is. This signal is then fed into a Digital to Analogue converter and then your tachometer is supplied with a specific voltage. So Im not sure if there is a specific "type" of signal that comes from the COP. Hope this helps somewhat.

It sounds like you set up the oscilloscope close to correctly though. If it were me, I would have the tach signal as the input to the O-Scope, and then have the other part of the probe wire grounded. Im assuming you hooked up the O-Scope when the engine was running and you have your COP's wired correctly (ground, voltage source, input from ecu, tach signal). Otherwise, you could try your pull up or pull down resistors or try inspecting the input signal from the ecu and see what you get.

Vic

[morgan]

what motor are the COPs going on? in terms of the 20v swap, the oem igniter is used. check the link in my sig to see how if youre interested.

[Jan Pedersen]

They are fitted to a 20V with VEMS ECU. So no igniter...

[jondee86]

If you are trying to drive an AE86 factory tacho you will not be able
to do it directly from any low level COP tacho output. The tacho needs
a voltage spike in the order of >30V, and you will only get this by using
the low level tacho output to drive a transistor that switches 12V to
ground thru an inductor. If you are not batch firing the COP's you will
have to combine as many signals as necessary.

Far easier to program one of the ECU aux outputs as "tacho" and use
that to switch 12V to ground thru the inductor. The inductor (old relay
coil) generates the flyback voltage spike for the tacho.

Cheers... jondee86

[Jan Pedersen]

I am currently using an output from the ECU. Problem is that the tachometer reads about 13% less than it should.

At first I used a tachobooster and thought the noise made the ECU cut out at 7200 rpm. So I changed the tachometer to accept a 12V signal but still cut out at 7200. Then I realized that the ECU output was the problem...

This made me wonder if I could use the COP feed back signal to get an accurate reading.

[assassin10000]

The igniter igf output is 5v or less iirc. You could try the old haltech trick of hooking the tach into the ground side of all the coils and using a 1ohm 50watt resistor to force a spike/signal like the original coil made.

Search as i think a few aussie guys did it years back.


I take it your ecu/software doesnt have a multiplier to correct displayed tach rpm?



Andrew

[jondee86]

This made me wonder if I could use the COP feed back signal
to get an accurate reading.

This (using the IGf) seems to be somewhat problematical. Since you have
the "tach" outputs on your COP's you may be able to find a solution along
the lines of this posting from another site...
http://www.miataturbo.net/megasquirt-18/toyota-cops-tach-output-pin-38130/

If, as suggested, the tach pin momentarily switches to ground after each
spark discharge, then by using a small relay coil to pull the tach pin up to
12V, you should be able to generate a voltage spike to drive your tacho.

Basically, this is how I drive my tacho, except that I use one of my ECU
aux outputs to switch the 12V line to ground. I used the coil out of a small
Toyota relay, and it works perfectly.

Cheers... jondee86