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Old 04-19-2014, 11:00 AM   #1
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Default Significant Spark Latency - COP or FM36-2??

So my new engine has both toyota coil on plugs and the FM36-2 trigger wheel running on a MS3. Fyi, it's a naturally aspirated engine.

Order of things I did:
1) Set base timing at idle with a timing light
2) Tuned engine on dyno, noted that it took a LOT of commanded spark at the high rpms to reach max brake torque timing, around 35 degrees advance on gasoline, about 6 more than normal.
3) Rechecked base timing with a timing light, but this time free revved it up to 6k rpm - Timing was retarding around 5 or 6 degrees up there!
4) In tunerstudio I set the spark latency to 140 microseconds, and this corrected the issues so timing holds constant throughout the rev range.

But, I was wondering if anybody else has noticed this issue, I'm trying to figure out if it's due to the coil packs (probable) or the FM trigger wheel (possible). Thoughts?
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Old 04-19-2014, 11:06 AM   #2
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Also, does anybody know what determines coil pack latency? Would a lower supply voltage at the coil cause it to discharge with a longer delay? I wouldn't think so?? I didn't install the capacitor for the COP, but have set my dwell using 'dwell by table' in tunerstudio so I can bump the dwell up to 3ms at high RPM to help account for any voltage loss as it pertains to stored coil energy.
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Old 04-19-2014, 11:54 AM   #3
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How did you check the timing while free revving? Did you lock the timing at 10* and just revved it and checked with the timing light?
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Old 04-19-2014, 12:04 PM   #4
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Originally Posted by speedengineer View Post
Also, does anybody know what determines coil pack latency? Would a lower supply voltage at the coil cause it to discharge with a longer delay?
It does but a tiny tiny amount, like less 0.1* at 6000 RPM.
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Old 04-19-2014, 12:19 PM   #5
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How did you check the timing while free revving? Did you lock the timing at 10* and just revved it and checked with the timing light?
Timing was locked down to 10deg for all the timing tests
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Old 04-19-2014, 12:19 PM   #6
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It does but a tiny tiny amount, like less 0.1* at 6000 RPM.
Thanks, good to know!
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Old 08-04-2014, 06:48 PM   #7
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Do you have your signal running the right polarity? The COP would burn out quickly if you try to invert the dwell signal, but your crank sensor signal may be the wrong polarity, firing from the trailing edge rather than the leading edge. There is a selector in the ECU to use positive or negative polarity. This could account for a consistent spark retard.
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