Needing to know the difference....

[Lizard]

Ok I did a VEMS install on a car with COP ign and after much struggling trying to get the 8x +5V logic level outputs to drive the 4 pin COP units, we gave up.
We ended up going to the 4 IAC channels (+12V) and drove the COP units with these and they fired perfectly right away.

Now I am both doing another install, and would like to also revert to the 8 logic level drivers on that install to get sequential.

So my question is what is the difference in the signal between the 8 logic level outputs, and the 4 IAC stepper outputs?

Are they both square wave? Is the only difference that one runs +12V and the other runs +5V? 
I am afraid I dont have access to that car for awhile to be able to put an oscilliscope on the two outputs myself and figure out the differences to know what is needed to fire them on this new project.

TIA
Colin

[mattias]

The best way is to use stepper outputs to drive active coils. 

The input impedance on the coils may be too low, the logic drivers must have a matched output impedance to be able to drive the output to a high enough voltage to trigger the logic level input on the coil.

As a measurement try 1k pullup on the logiclevel output to +5V.
If the result is 1.7V than 510Ohm internal resistance, this was popular on old boxes.
If more like 0.9V or 1V then you have 255 Ohm which should be enough to drive most active coils.

Another method, which may not be as popular requires external pull-ups (500 Ohm) towards +12V and  connect these  to regular IGBT outputs. It is very important that the power to the pull-up is taken from the fuel pump relay output so that the ECU has been able to initialise before the signal to the coils can be conditioned.

[Denmark]

"""Another method, which may not be as popular requires external pull-ups (500 Ohm) towards +12V and  connect these  to regular IGBT outputs. It is very important that the power to the pull-up is taken from the fuel pump relay output so that the ECU has been able to initialise before the signal to the coils can be conditioned.""""


this is what i have done on all the Impreza builds i have made, 12v pullup on the IGBT,and run inverted, as they trigger on 12v, but i have used the 12volt feed right at the ecu 12v input,
Can that maybe be the trooble of the Subaru starting, with backfire and difficult/non starting?, but if we pushstart the car it starts right away!.


Thanks,
Skassa

[gunni]

You´d have to log the oscilloscope injector and ignition outputs at starting to see if that is the problem or the trigger.

[mattias]

this is what i have done on all the Impreza builds i have made, 12v pullup on the IGBT,and run inverted, as they trigger on 12v, but i have used the 12volt feed right at the ecu 12v input,
Can that maybe be the trooble of the Subaru starting, with backfire and difficult/non starting?, but if we pushstart the car it starts right away!

You should definately wire the pull-up to something that hasn't got power before the ECU has initialised the outputs correctly.
If the coil receives a "positive pulse" before the ECU has the chance to ground the outputs (as they are normally when inverted) the coils are quick to fire a spark on the falling edge when the outputs are grounded just 60-70 ms after the ECU boots up.

This cause major head-aches for me too the first time I did it because all the coils would discharge at once when the ignition was turned on, which blew the fuse. I suspect you didn't use a fuse or you would have noticed.

[Lizard]

Thanks for the responces guys.

I actually managed to figure out what the problem was.

The +5V reference signal (logic level) did not have enough milliamps to drive the COP units.
They required a +5V logic level signal that had a minimum of 18ma.
I put a 100 ohm resistor from the 5VRef TPS line to each of the logic outputs and that curred the problem. Now they work perfectly!

Thanks again