JumpyRoo

It looks like a starter. And it confuses me.

scathcart

It is a replacement for a distributor. It uses a gear off of the eccentric shaft to electronically record where the eccentric shaft is in rotation. This signal is interpretted by the ECU, and spark signal is sent according to ignition mapping and load to the coils.

NZConvertible

It's a little more than that. The CAS sends two signals to the ECU: crank angle (duh!) and engine speed.
The uses for engine speed are pretty obvious. Fuel requirements and ignition timing are calculated from look-up tables of load vs. rpm. The ECU measures load from the airflow meter and rpm from the CAS and uses that info to calculate injector pulsewidth and the correct amount of ignition advance/retard. As well as that there's all the other things the ECU does at various engine speeds, like twin-scroll, 6PI and VDI actuation, emission controls, etc.
The crank angle signal tells the ECU where the engine is in its rotation so that both the spark plugs and the injectors are fired at the right time. The ignition timing aspect is similar to how a dizzy works, but it's also important to fire the injectors at the right time in the crank's rotation, to match up with the port's opening and closing.
Hope that answers your question JumpyRoo.

JumpyRoo

Hm. So can a wire be led off it to tell an aftermarket item engine speed, or would it be better worth my while to take this information from another center? Like the computer?

Is this a rotary only item, not found in cylinder engines? I thought we had distributors in the sparkplug cap?

JumpyRoo

Oh, BTW: Thanks, both of you.

NZConvertible

Most aftermarket tachos, rpm swtiches, etc take their signal from an ignition coil. Both the leading and trailing coils actually have plugs on their wiring to allow a tacho (or whatever) to be plugged straight in. Don't mess with the CAS signal, it's too important to risk upsetting it. All EFI engines have a sensor like this, it's the main input signal along with the load sensor (AFM or MAP sensor). Some attach direct to the nose of the crank (like the FD), some to the camshaft, but all have them in one form or another. Not quite sure what you mean there, but older rotaries that have carbs or fuel-only EFI systems have an ignition distributor in that location instead. In fact Madza dizzies and CAS's are interchangable.

vicious525E

so which do you wire a tac up too, the leading ing coil or a trailing? and where does the stock tack hook up at? mines not working... also would it matter if you swaped your cas for a different one, like a fd one, would it change anything at all?

scathcart

You could hook up an aftermarket to either, but which coil you place it on changes what setting you should leave it on.
Since the leading coil fires one wastespark, and therefore fires twice as much, you would have to set an aftermarket tach to V8 mode.
If you hook up an aftermarket tach to the trailing coil, you should set it to 4 cylinder mode.

The stock tach wires into the negative trailing coil wire. Check for a broken lead by following the FSM wiring diagram.

I believe you cannot swap to an FD CAS, but I am not positive on that. The CAS's are all interchangalble among Gen 2's though. Turbo or NA does not make a difference.

RETed

(Crap, I hit the wrong button and edited the original post by vicious525E - sorry about that!)

That's is correct.
The FD3S ignition trigger spits out a different signal, so the stock FC3S ECU will barf.

Other than that, the timing is the same.

My 2 cents...
The CAS spits out two separate signals - i.e. 4 wires.&nbsp One pair is for "home" and fires everytime the rotor hits TDC.&nbsp The other pair is a "sync" signal, and it "fires" every 30 degrees of "crank" rotation - i.e. fires 12 times per revolution of the "crank".&nbsp These signals are extremely low power - under 1VDC, so they are no use to anything except the ECU itself.&nbsp Now, just to confuse everyone, the stock FC CAS rotates at *half-speed*, so the CAS spins only 180-degrees per full revolution of the "crank".&nbsp If you pop the cap off the CAS, you'll see two teeth on the top and 24 teeth underneath.


-Ted

Snrub

iTrader: (1)

Seems like a good time to mention this:
I took a scope to the RPM signal that the S-AFC taps into. P-P is just under 5V (I got ~4.6V). It's cycle occurs 2X every e-shaft rotation. This is rough, but at 3000rpm the bottom of the wave goes from 0 to .3V (right to left, straight line increase) for 9ms, the top varies .2V left to right) for 2ms. Obviously if you double this you get 22ms total instead of 1/(3000/60) = 20ms, so that's not 100% accurate. You can figure out what it should be for different revs now, etc.

Maybe that'll help someone, somewhere.

Piranha

Ted... how does the CAS know the "home" position? so the CAS spins twice every RPM.. sending the home position twice. After my Trailing coil problem, I swapped CAS, the problem stayed, swapped mine back, and the problem dissapeared. Its weird. AH!

cbrock

iTrader: (1)

I've always wondered how this works with aftermarket ECU's. I know on hitmans web site you just spice into the CAS and adjust the haltech. With the TEC's you use their crank trigger wheel. How the hell does that setup??? I've seen crank triggers on V8's being off the main pulley. Anyone got a pic of this on a rotary. Inquiring minds want to know.

RETed

Nah, you've got that backward (or did I describe it wrong?) - the CAS spins only half a rotation versus every RPM.&nbsp Thus the CAS spins one complete every two revolutions of the engine.

That still baffles me - is the front trailing coil T1 and the rear T2?


-Ted

RETed

The Electromotive units run off a 60-2, which is a 60 tooth trigger with 2 missing teeth to signal TDC.&nbsp This is how it knows when TDC is...


-Ted

Piranha

Yep, front is T1, rear is T2. At least, I think so. I was looking at the labels, nonetheless. But it switched, twice. I am baffeled indeed. I AM running an N332 ECU, and it was originally a 333, but I fried it.

HAILERS

http://www.teamfc3s.org/info/articles/demystifying.html

Piranha

How about you "demystify" WTF happened Hailers??? :P :P :P