INSW20 Posted May 7, 2021 Report Share Posted May 7, 2021 I've noticed several times where my dwell time drops significantly below what's shown in my dwell table. Log, cal, and screenshot attached. It's especially prevalent at the end of the log when it's sitting at idle. Any ideas what could be causing this? Quote Link to comment Share on other sites More sharing options...
essb00 Posted May 7, 2021 Report Share Posted May 7, 2021 Any reason why your dwell control table is Batt Voltage vs MGP? Typically it is Batt Voltage vs Engine Speed (RPM) It could be that the tiny fluctuations on MGP (not logged due to filtering, & PC logging limited to 40Hz or ECU logging limited to 100Hz) are causing those dwell time dips. Better change it to Batt Voltage vs Engine Speed (RPM). Quote Link to comment Share on other sites More sharing options...
INSW20 Posted May 7, 2021 Author Report Share Posted May 7, 2021 20 minutes ago, essb00 said: Any reason why your dwell control table is Batt Voltage vs MGP? Typically it is Batt Voltage vs Engine Speed (RPM) It could be that the tiny fluctuations on MGP (not logged due to filtering, & PC logging limited to 40Hz or ECU logging limited to 100Hz) are causing those dwell time dips. Better change it to Batt Voltage vs Engine Speed (RPM). Mostly that my understanding is that spark voltage requirements are more closely tied to MGP than RPM. I can certainly change it back and re-test. I guess what I don't understand is that my dwell map is constant across all MGP currently, so even if it were dropping off the edge of the map, shouldn't it extrapolate/extend the last column values? Quote Link to comment Share on other sites More sharing options...
Adamw Posted May 7, 2021 Report Share Posted May 7, 2021 The logged dwell is the actual dwell that was finally applied, not the value that was commanded from the dwell table. If ignition timing or crank speed changes after the ecu has already started charging the coil - then the ecu needs to shorten or stretch dwell to make sure the spark still occurs at the right place. Obviously correct spark angle is far more critical than correct dwell time. In your case it appears to be caused by over aggressive idle ignition timing. So you are constanting changing ignition timing after the dwell event has started. The dwell will probably be bouncing around a lot more than the log shows but at 40Hz you only pick up the occasional occurance. Notice in pic below the dwell spikes are only when the idle ignition is bouncing around. It is totally fine to leave it like this if it idles well, however, I suspect you will possibly get a smoother idle by making the idle ign control less agressive. Quote Link to comment Share on other sites More sharing options...
INSW20 Posted May 7, 2021 Author Report Share Posted May 7, 2021 To close the loop on this, here are my trigger scopes. Quote Link to comment Share on other sites More sharing options...
Adamw Posted May 8, 2021 Report Share Posted May 8, 2021 Yeah scopes look ok. INSW20 1 Quote Link to comment Share on other sites More sharing options...
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