Discussion
As in the amount of time the coil is powered for, not ignition timing
If you can 2d map this would you expect to change it dramatically with engine speed ?
In a old school ignition system it was, ie at lower revs the points are closed for longer the coil is powered up for longer. Spark duration would be dependent on nothing but coil/condenser combination
OTOH I would have thought that if you could specify the coil time, there would be an optimum timing dependant I assume (dangerous I know) on the coil alone
And here's the big question, how can I find out what that timing should be ? The car in quextion (standard VVC k series) had a starting problem, but dramatically increasing the coil timing on cranking made a massive difference (I only did this as it "felt" like a weak spark) (changed from 3 to 6 ms)
If you can 2d map this would you expect to change it dramatically with engine speed ?
In a old school ignition system it was, ie at lower revs the points are closed for longer the coil is powered up for longer. Spark duration would be dependent on nothing but coil/condenser combination
OTOH I would have thought that if you could specify the coil time, there would be an optimum timing dependant I assume (dangerous I know) on the coil alone
And here's the big question, how can I find out what that timing should be ? The car in quextion (standard VVC k series) had a starting problem, but dramatically increasing the coil timing on cranking made a massive difference (I only did this as it "felt" like a weak spark) (changed from 3 to 6 ms)
Incorrigible said:
As in the amount of time the coil is powered for, not ignition timing
If you can 2d map this would you expect to change it dramatically with engine speed ?
In a old school ignition system it was, ie at lower revs the points are closed for longer the coil is powered up for longer. Spark duration would be dependent on nothing but coil/condenser combination
OTOH I would have thought that if you could specify the coil time, there would be an optimum timing dependant I assume (dangerous I know) on the coil alone
And here's the big question, how can I find out what that timing should be ? The car in quextion (standard VVC k series) had a starting problem, but dramatically increasing the coil timing on cranking made a massive difference (I only did this as it "felt" like a weak spark) (changed from 3 to 6 ms)
Measure the current draw of the coil and increase dwell until it stops increasing. Although that'd not to say you wont fry the coil doing this.If you can 2d map this would you expect to change it dramatically with engine speed ?
In a old school ignition system it was, ie at lower revs the points are closed for longer the coil is powered up for longer. Spark duration would be dependent on nothing but coil/condenser combination
OTOH I would have thought that if you could specify the coil time, there would be an optimum timing dependant I assume (dangerous I know) on the coil alone
And here's the big question, how can I find out what that timing should be ? The car in quextion (standard VVC k series) had a starting problem, but dramatically increasing the coil timing on cranking made a massive difference (I only did this as it "felt" like a weak spark) (changed from 3 to 6 ms)
Various coils can handle various dwell times, but whether or not you need to run the maximum possible dwell is another matter.
And some ecu's will increase dwell on cranking, or similarly on low battery voltages to ensure spark is maintained.
Cheers for the replies guys
Excellent article Mr "the end" I'm very familiar with points condenser etc (to the point of changing springs, weights etc to customise the advance curve etc etc) but I'm still on the steep learning curve part of ECU tinkering
I'm thinking, with the settings I currently have, I'm unlikely to blow anything up
also the increased charge time (effective dwell) must have made the all important difference on starting. I'm assuming that I'm not reaching any saturation point at this level (although I'd like to check), but even if I do, it's only for a few seconds at most.
Also, while probably not optimised, about a 3ms dwell seems to work well for everything apart from cranking (any changes you may see fit I would love to test) but the current map appears to be a base map with no changes
Although if anyone had any other numbers they'd recommend or any specific current readings I should be scared about, please let me know
Thanks again
Excellent article Mr "the end" I'm very familiar with points condenser etc (to the point of changing springs, weights etc to customise the advance curve etc etc) but I'm still on the steep learning curve part of ECU tinkering
I'm thinking, with the settings I currently have, I'm unlikely to blow anything up
also the increased charge time (effective dwell) must have made the all important difference on starting. I'm assuming that I'm not reaching any saturation point at this level (although I'd like to check), but even if I do, it's only for a few seconds at most.Also, while probably not optimised, about a 3ms dwell seems to work well for everything apart from cranking (any changes you may see fit I would love to test) but the current map appears to be a base map with no changes
Although if anyone had any other numbers they'd recommend or any specific current readings I should be scared about, please let me know
Thanks again
In my experience 3.0m/s is pretty standard for a single coil application. Stevie's suggestion is the correct way of determining coil dwell.
If you have a variable power supply, you can use it to power the coil independently of the car's 12v system. With this in place you can use Stevie's method to find the dwell for different voltages. These findings can be input in to a 2d table dwell vs battery voltage.
You could try asking someone like Dave Walker of Emerald ECU's for a 2d dwell table for your coil. Assuming it is a standard K series part.
If all else fails you can take a guess at a table using 6m/s at 7v and interpolate up to 3m/s at 14v. The amount of time that the coil will see 6m/s at 7v is unlikely to cause any damage.
Steve
If you have a variable power supply, you can use it to power the coil independently of the car's 12v system. With this in place you can use Stevie's method to find the dwell for different voltages. These findings can be input in to a 2d table dwell vs battery voltage.
You could try asking someone like Dave Walker of Emerald ECU's for a 2d dwell table for your coil. Assuming it is a standard K series part.
If all else fails you can take a guess at a table using 6m/s at 7v and interpolate up to 3m/s at 14v. The amount of time that the coil will see 6m/s at 7v is unlikely to cause any damage.
Steve
Cheers, it is an Emerald ECU on it. and yes I can change the coil time WRT battery voltage. Although, as the alternator output is fairly steady I'm thinking this is not as important as getting the cranking time sorted (especially where the starting issue is concerned (The cranking coil time is a completely separate value)).
I may do some more experimentation but for now, and especially as these are old standard coils (2), I'll check the coil current isn't excessive and leave it there.
Thanks again
I may do some more experimentation but for now, and especially as these are old standard coils (2), I'll check the coil current isn't excessive and leave it there.
Thanks again
During cranking the alternator is not providing any input, and the battery voltage will sag massively due to the high current and internal resistance of the battery and series resistance of the wiring loom etc. Hence, often true voltage measured at the coil pack(s) during cranking can be less than 8volts. If this is the case, then the increase in dwell time is entirely commensurate.
At the low speeds and highly intermitent operation associated with cranking, even with a heavily oversaturated coil you are unlikely to actually be able to break anything! if you are worried about dwell at other speeds, then i can recommend getting some of those stick on temp tabs and putting them on the top of the coil packs. Anything much over 120degC and you need to be worried
At the low speeds and highly intermitent operation associated with cranking, even with a heavily oversaturated coil you are unlikely to actually be able to break anything! if you are worried about dwell at other speeds, then i can recommend getting some of those stick on temp tabs and putting them on the top of the coil packs. Anything much over 120degC and you need to be worried
Max_Torque said:
During cranking the alternator is not providing any input, and the battery voltage will sag massively due to the high current and internal resistance of the battery and series resistance of the wiring loom etc. Hence, often true voltage measured at the coil pack(s) during cranking can be less than 8volts. If this is the case, then the increase in dwell time is entirely commensurate.
Indeed, and give that the revs at cranking are ~ 280 a points system would give a dwell ~ 4X that of the dwell at idle...The questions were really: Why would whoever mapped it NOT increase the cranking dwell, and would 2X be enough ?
Anyway, it started after half a seconds cranking this morning, which is a massive improvement. I need it to get a bit colder to check it works at all temperatures, but I reckon we're done
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