Dwell observations on the Toyota COP.
02-22-2010, 10:48 AM
#21
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Yes, I believe Brainey has it right.
I do like the MS2s approach to dwell correction much better than the MS1s, insofar as that it's easily user-configurable. Hacking the code isn't particularly difficult (particularly with MS1, where it's a nice, monolithic package) however I really hate forking software needlessly. A year or two down the road, I (or the new owner of the car) will put new code onto it, forget about the fact that the old code had been manually hacked, and wonder why they're getting misfires all of a sudden.
No, I think I'll just stick with my original solution, which is to up-rate the specified dwell. It works fine, introduces the fewest variables, and is easily copied by folks who don't own scopes and don't like to mess with compiling their own code.
I do like the MS2s approach to dwell correction much better than the MS1s, insofar as that it's easily user-configurable. Hacking the code isn't particularly difficult (particularly with MS1, where it's a nice, monolithic package) however I really hate forking software needlessly. A year or two down the road, I (or the new owner of the car) will put new code onto it, forget about the fact that the old code had been manually hacked, and wonder why they're getting misfires all of a sudden.
No, I think I'll just stick with my original solution, which is to up-rate the specified dwell. It works fine, introduces the fewest variables, and is easily copied by folks who don't own scopes and don't like to mess with compiling their own code.
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02-22-2010, 11:43 AM
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And of course, for those of us running in wasted-spark mode, the problem is amplified, as the total draw on the wire supplying the coils is twice what I observed on a single coil. 22 amps is a hell of a lot of current for what I recall to be a 16ga wire. If these cars fell under the purview of the NEC for cabling vs. current, we'd be in violation.
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02-22-2010, 12:05 PM
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The gist of my findings here are basically that Jason's data is correct insofar as 2.5 ms dwell, with the caveat that, at least in my system, they are correct for whatever supply voltage is actually being encountered at the coils (which I should probably measure), and must not be derated based upon the ECU's observation of system voltage.
I should note also that in my setup, there are a pair of 4,700 uf caps in parallel across the coils' supply, located at a point between the old igniter connector and the back of the head.
I wonder if this accounts in some way for the knee in the current profile that I observed in my analysis?
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02-22-2010, 12:09 PM
#28
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The MS-II default curve is:
It runs fine and I have my dwell set to 2.5ms. The manual suggests it'll be fine for 99% of users.
Based off Jason's dwell curve, I thought it might be more ideal to go to:
but it's definitely going to be dwelling less.
Code:
Voltage Correction 6 500% 8 248% 10 168% 12 128% 14 102% 16 88%
Based off Jason's dwell curve, I thought it might be more ideal to go to:
Code:
Voltage Correction 6 180% 8 160% 10 120% 12 100% 14 86% 16 76%
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02-22-2010, 12:24 PM
#29
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So far as I can tell, my own observations, Jason's observations, and the MS-II default curve all match up. If you dwell the coil for 2.5ms at what is most likely 12 volts or so (as measured at the coil) you get peak energy.
Since voltage as measured at the ECU is always going to be higher than actual voltage at the coil, I'd suggest sticking with the MS-II default.
Since voltage as measured at the ECU is always going to be higher than actual voltage at the coil, I'd suggest sticking with the MS-II default.
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02-22-2010, 12:42 PM
#32
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For all I know, it could just be an artifact of my (relatively cheap) current probe. This is the first time I've done this sort of thing with my new Chinese unit as opposed to the $2,500 Tektronix one we have in the lab.
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02-22-2010, 03:52 PM
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If that were the case, I'd expect the slew rate to go down, not up.
For all I know, it could just be an artifact of my (relatively cheap) current probe. This is the first time I've done this sort of thing with my new Chinese unit as opposed to the $2,500 Tektronix one we have in the lab.
For all I know, it could just be an artifact of my (relatively cheap) current probe. This is the first time I've done this sort of thing with my new Chinese unit as opposed to the $2,500 Tektronix one we have in the lab.
V = L * di/dt
For a given applied V, if L goes down, di/dt (rate of change or slope of current) goes up.
I get the same exact slope with a $30k setup at work.
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02-22-2010, 04:30 PM
#35
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Hmmm. Well, I admit that I suck with magnetics. Anything involving Q falls into the realm of FUD so far as I'm concerned. We have a guy here at work who absolutely revels in it, but he frightens me.
Several years ago, I did this exact same test with my then-current setup, involving the stock '90-'93 coils, using the expensive Tek scope from work. Here's what I saw:
You can see that the current rise rate is slowing down as primary current increases. Knowing no better, I simply assumed this to be the natural behavior of an ignition coil primary. In this capture, the stock Mitsu igniter is in place, so this may simply be an artifact of that device (a "soft" current limit, as opposed to the Toyota's hard limit) though of course this is only speculation.
The leveling-off continued as dwell was increased beyond what's shown in this image, until a knee point was reached which I judged to correspond to the saturation point.
Several years ago, I did this exact same test with my then-current setup, involving the stock '90-'93 coils, using the expensive Tek scope from work. Here's what I saw:
You can see that the current rise rate is slowing down as primary current increases. Knowing no better, I simply assumed this to be the natural behavior of an ignition coil primary. In this capture, the stock Mitsu igniter is in place, so this may simply be an artifact of that device (a "soft" current limit, as opposed to the Toyota's hard limit) though of course this is only speculation.
The leveling-off continued as dwell was increased beyond what's shown in this image, until a knee point was reached which I judged to correspond to the saturation point.
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