Mazda CAS

All Megasquirt 1 support questions. See also the Documentation

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Postby gregsalt » Sat Apr 09, 2005 7:20 am

I have a working setup for a Miata, that uses 2 hall triggers, but one has 4 slots, while the other has 2.

are you sure that yours has only 1 slot? if so, is this slot timed tdc cyl 1 on firing stroke or what?
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Postby RyanPzz » Sat Apr 09, 2005 10:32 am

You wouldn't need to use the second wheel decoder if you plan to use the disty. The 4 evenly spaced windows will be fine to trigger the megasquirt in MSNS mode, for a single coil ignition.
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Postby Jeff20B » Sun Apr 10, 2005 3:31 pm

I think fan/out4 is LED 18. It can't flash as quickly as an LED so it only flashes every other time.
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Postby RyanPzz » Mon Apr 11, 2005 3:36 pm

Why would the secondary trigger help the low end and throttle response? It depends on the primary trigger for timing still just as it does now. I guess you could be referring to the use of wasted spark coilpacks, but on a 4 cylinder the benefit is neglidgable, compared to say a V6 or V8.

The primary benefit to coilpacks is the fact that there is still enough time at high rpms between each spark to completely charge the coil. This is due to each coil having 1/3 (V6) or 1/4 (V8) the duty of a single coil disty setup.

Assuming an "ideal" dwell time of 3.6ms, a V6 you start to lose spark intensity at ~5600 rpm since the time between each spark is less than 3.6ms. On a V8 the problem is even worse beyond 4200 rpm you lose spark power. This is because as cylinder number increases, spark events per rev also increases.

On a 4 cylinder engine, only 2 sparks occur per rev of the engine. At 8500 rpm you fall just below the "ideal" dwell period. 8500 rpm is more than most people rev out their 4 cylinders, but even still there is enough residual spark past 8500 to fire the cylinder. Consider the case with with the V8. Ideal dwell time is overcome at 4200 rpm, and yet V8's rarely just plain shut off at 4500 rpm. The spark may not be as hot, but still enough to fire the cylinder.

In your case, where the problem you have is occuring at low rpm. Secondary trigger, and coilpacks is not likely to help you out. There may be a pre-existing problem causing the symptoms you described, or there may be an issue with tuning. Perhaps you have too much acceleration enrichment? I noticed on my car hte accel enrich. was WAY off after the swtich to 024.

Either way I talked briefly about the DSM CAS and secondary trigger setup here:

If you can get your car running properly in MSNS mode you're probably better off just running that. I just want to make sure you realize that you're unlikely to resolve the issues you described by switching to the decoder, especially if you plan to retain the stock disty and single coil setup. Whole lot more wiring, virtually no benefit.
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