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Old 12-30-2015, 07:08 PM   #5
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Join Date: May 2014
Location: Palm Beach County, FL
Posts: 1,811
Originally Posted by bmwman91 View Post
Basically, the factory dwell is 3.6ms on average. It jumps around a lot, from 3.0 to 4.2ms and it seems totally random. Maybe the Motronic is old and slow or something, or maybe it has to do with the timing advance changing during the dwell period or something. Anyway, 3.6ms of dwell with the M52 coils on our cars makes for an 8 Amp primary current and the spark duration ranges from 2.2ms at idle to 0.9ms at redline.
Interesting. With the voltage correction I probably average 3.6ms too. Stays steady with MS though - it's nice to be able to see exactly what's going out by plugging in your laptop.

Originally Posted by bmwman91 View Post
Any chance that you can post up the settings you use for the idle control (assuming you use the stock ICV)? How about the tach and MPG gauges? From what I understand, the tach takes a 50% duty cycle square wave with 2 pulses per revolution. As far as the MPG meter, I need to get in there with a scope.
Shortly after I started to get it dialed in, my ICV stopped working correctly - it would just creep wide open and stay there, not responding to changes in duty cycle. I haven't bothered to replace it yet because they're so expensive.

The MPG gauge I haven't figured out, and likely won't ever try - fuel economy doesn't really matter to me, if I were to try and figure it out it would be to make my own boost mpg gauge. I suppose it wouldn't be so hard, I don't have a function generator though, or a stock car to probe with a scope. The tachometer is happy with the 5V square wave output straight from the MS board, no mods required, set to normal speed which is one pulse per revolution.
'91 318is, M20B25, T3/T04E 60 trim (15psi), megasquirt, coilovers, Z3 rack, cold AC
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