badge988

Ive been looking around on the engine mgt forum about the 'squirt-II ignition capabilities and even the webpage itself however Im missing something here. Why couldn't the stock CAS be used to trigger the ignition section of the squirt-II and fire the stock wasted spark coils? Do the ignitors use an inboard switch to fire them or does the stock ECU do the switching? I have not pulled the coils out of the car to verify this myself but plan to.

Here is what Im dealing with so far. 1987 FC turbo-II thats getting the motor overhauled and transmission inspected. The entire driveline is out of the car right now and the stock ignition harness is a wasted pile of colored copper. Reason for the overhaul was water on the front plugs and I found the front iron water seal groove broken out in several places.

My goal is to rebuild using all stock parts except the stock fed computer. I was looking at alternative computers along with the JDM ECU however another member pointed me in the direction of the 'squirt computers and I came across the Megasquirt-II that had ignition control. Knowing Im going to pound around 15 PSI of boost at times I didnt like the idea of "fooling" the stock ECU into thinking the boost was lower as it would also cut back fuel to keep it within the correct ratios for the programmed boost map. I tend to run any turbo motor a little fat on the mixture for cooling but going that route with larger injectors were only asking for trouble in terms of poor control.

So despite the fact the squirt-II has an issue with lead/trail spark what would keep me from retaining the stock CAS and coils? I plan on using a delay circuit to fire the trailing anyway but even if its lost I dont see much of a performance hit. I want to keep the engine bay as close to stock and clean as possible. Also doesnt the GSL-SE distributer use vacuum and centrifugal advance for timing control?

Your help and input both good and bad is greatly valued.

988

muythaibxr

You probably could trigger the stock leading using ms2 but you'd have to mod your CAS so it only has 4 teeth. It wouldn't work with a stock CAS because the ms2 doesn't have a wheel decoder yet. MSnS-extra has a wheel decoder however, and I've used that on tofuball's car running stock leading with a stock CAS for several hundred miles w/o problems. As soon as he's done repairing the car from his accident, we'll be adding trailing as well.

Just wait another couple of weeks, and the MSnS-extra code will be tested with stock leading/trailing. The only hold-up for testing is waiting for tofuball to be ready to start driving the car again. I have already tested trailing on the oscilloscope and it looks pretty solid; I'm going to do more testing on the oscilloscope before putting it in a car, but I don't forsee any problems.

badge988

Help me understand something here so I can get the big picture.

I pulled the cover off the CAS and noted the 2 pickups and triggers, one toothed and one with just two wings on it. Im assuming the toothed wheel sends the computer a "countdown" between pulses generated by the other rotor. Now are those pulses from the 2 winged rotor in step with the firing of the engine or are they to only tell the computer when the engine has completed a full revolution?

I dont fully understand the timing sequences of the stock computer with respect to coil firing and injector firing. Im also under the assumption that the gear ratio drive for the CAS is such that it completes a full revolution in respect to each rotor face that is in compression stroke.

Ive never torn down a 12A or 13B distributer in the past so I dont know what the real timing sequence is, the reason I want to understand this is I would like to use the stock CAS to trigger ignition events with the 'squirt-II and retain the stock "wasted spark" coils. Im already designing a delay circuit to work with the trailing coils and will vary the delay in relation to engine speed eg 3 deg delay at idle down to say 1.5 deg delay at 6000 RPM. Some bugs to work out but will post the circuit for all to use when its perfected. The BASIC stamp is a wonderful thing!

Just need some help with the stock CAS and understanding its timing events.

Thanks guys

988
1987 Turbo-II, sons car

pmrobert

http://www.teamfc3s.org/info/articles/demystifying.html gives a decent description of the stock 2nd gen ignition system and how the 2 trigger wheels' output interacts. In reference to your plan for a simple delay circuit to fire the trailings: You not only have to delay the spark, you have to select the rotor, that's one of the functions of the 2 tooth trigger wheel. If you try to waste spark the trailings you will have the trailing spark in the non-firing chamber occurring at the end if the intake stroke in that chamber. That won't work and makes wonderful backfires out the intake tract. The stock trailing coils have a select line on them so most of the hardware work is done. The Extra code is very close to having fully functional programmable trailing split. I'm currently flow charting a scheme for the MSII where a couple of the IAC pins would be sacrificed and reset to work as timers.

-Mike

muythaibxr

The CAS turns half a rev for every full rev of the engine... so in the megasquirt, you'd configure this as a 12 + 1 wheel.

I'm not sure what the stock computer does, but I have it configured in tofuball's car so that the tooth right after the 2 tooth wheel is the 60 deg btdc tooth, and the tooth that I set the trigger angle based on. I think the 2 winged rotor is just to tell the ECU in stock configuration when TDC for a rotor is coming up soon. In the megasquirt, it's used to reset a tooth counter.

pmrobert

In the stock ECU, the 2 tooth trigger is used to identify rotor #1 TDC. That's how it knows to make the select line on the T coil high or not.

-Mike

badge988

Ok so what tells the ECM when to actually fire chamber-1 trail when its time without any sort of common index if the CAS is symmetrical in teeth for both the trigger and countdown? They both look the same and on a 'scope running off a small motor the outputs look symmetrical.

988

pmrobert

The 2 teeth on the top wheel correspond with rotor 1 TDC; rotor 2's is TDC 90* CAS/ 180* crank away there is no tooth oon the upper wheel for this position. Each tooth on the 24 tooth wheel is 15*CAS, 30* crank apart, the ECU uses this for instantaneous engine speed to figure out where/when the coil should be charged/discharged. The "countdown" is not necessarily set in stone - the ECUs usually calculate engine speed and position based on 1) an index, in this case the top wheel, and 2) engine speed based on the time delay between teeth and 3) total number of teeth sensed since index. Some setups, like Ford's EDIS, use a 36 tooth wheel on the crank with a tooth missing. This is termed 36-1 encoding. The Mazda CAS is a 12+1 encoder - the wheel are actually 24 and 2 but run at half crank speed. And yes, I know it's an eccentric shaft. There are many schemes with which engine position and speed is determined, there is no standard. I currently use a modified 4 tooth CAS (the bottom wheel has had 20 teeth ground off it leaving 4 teeth at 180* crank/90* CAS offset, see http://smrmicro.com/v-web/gallery/ ) waste firing leading only, no index required as all triggers are TDC of one rotor or the other; since you can get away with waste firing leading, this works fine. The details are in the software, most of which we are not privy too, like Mazda's. That's a good question you ask and this can be a difficult subject to fully comprehend and/or explain.

-Mike

cafcwest

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