A better Spark Out circuit.
09-08-2009, 03:15 PM
#111
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You can also rev up the motor to maybe 3,000 before you shut it off, and floor the pedal just as you turn the key. This will be more effective at clearing the chambers.
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12-16-2009, 12:01 AM
#113
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I'm gonna bring this one back from its slumber since I noticed a phenomenon after installing my COPs that may be applicable to the pop on startup.
I bought some 10,000 uF capacitors for building my COPs harness. I built it so 1&4 and 2&3 were completely separate from each other from the stock coil pack connectors to their respective pairs of COPs. I installed a 10,000 uF cap on each. In retrospect this was probably excessive because the power and ground for all four COPs probably share common connections before being split in the stock harness, but as it is I have 20,000 uF of Panasonic TSHA goodness on my ignition.
On the stock coil pack, when I'd shut the car off the motor would stop quickly. With the COPs in there it's like the motor shuts down more gently. It's markedly less abrupt, like it runs for another weak revolution or two. It happens 100% of the time. My hypothesis is that my 20,000 uF has enough stored energy to fire the plugs once more and burn that little bit of excess fuel that makes it into the cylinders from the time the injectors stop injecting until the pistons actually stop moving.
BTW, on shutdown I'm just turning the key back one click. It probably makes a difference because it will still need to be "on" in order for MS to see the engine rotation and trigger the coils. I think.
Is it possible that those with the fuel pop on startup could partially ameliorate the problem with some extra capacitance in their COPs? And what are the potential downsides, if any, of said extra capacitance? I have not yet installed my 550s but I will be curious to find out if I ever have the startup pop.
I bought some 10,000 uF capacitors for building my COPs harness. I built it so 1&4 and 2&3 were completely separate from each other from the stock coil pack connectors to their respective pairs of COPs. I installed a 10,000 uF cap on each. In retrospect this was probably excessive because the power and ground for all four COPs probably share common connections before being split in the stock harness, but as it is I have 20,000 uF of Panasonic TSHA goodness on my ignition.
On the stock coil pack, when I'd shut the car off the motor would stop quickly. With the COPs in there it's like the motor shuts down more gently. It's markedly less abrupt, like it runs for another weak revolution or two. It happens 100% of the time. My hypothesis is that my 20,000 uF has enough stored energy to fire the plugs once more and burn that little bit of excess fuel that makes it into the cylinders from the time the injectors stop injecting until the pistons actually stop moving.
BTW, on shutdown I'm just turning the key back one click. It probably makes a difference because it will still need to be "on" in order for MS to see the engine rotation and trigger the coils. I think.
Is it possible that those with the fuel pop on startup could partially ameliorate the problem with some extra capacitance in their COPs? And what are the potential downsides, if any, of said extra capacitance? I have not yet installed my 550s but I will be curious to find out if I ever have the startup pop.
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12-16-2009, 12:40 AM
#114
On the stock coil pack, when I'd shut the car off the motor would stop quickly. With the COPs in there it's like the motor shuts down more gently. It's markedly less abrupt, like it runs for another weak revolution or two. It happens 100% of the time. My hypothesis is that my 20,000 uF has enough stored energy to fire the plugs once more and burn that little bit of excess fuel that makes it into the cylinders from the time the injectors stop injecting until the pistons actually stop moving.
BTW, on shutdown I'm just turning the key back one click. It probably makes a difference because it will still need to be "on" in order for MS to see the engine rotation and trigger the coils. I think.
Is it possible that those with the fuel pop on startup could partially ameliorate the problem with some extra capacitance in their COPs? And what are the potential downsides, if any, of said extra capacitance? I have not yet installed my 550s but I will be curious to find out if I ever have the startup pop.
BTW, on shutdown I'm just turning the key back one click. It probably makes a difference because it will still need to be "on" in order for MS to see the engine rotation and trigger the coils. I think.
Is it possible that those with the fuel pop on startup could partially ameliorate the problem with some extra capacitance in their COPs? And what are the potential downsides, if any, of said extra capacitance? I have not yet installed my 550s but I will be curious to find out if I ever have the startup pop.
You know, I never thought about it that way, saying that after turning the motor off, it burns the left over fuel because of the leftover capacitance that caps give. I have the same 10,000µF capacitors for power stability to my COPs, but I dont have any of that pop issue most MS users have when using the old spark circuit.
But I do have that same "symptom" you describe of having the motor turn off with a delayed reaction, instead of turning off instantly.
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12-16-2009, 12:52 AM
#115
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If one coil (or one pair) was already in dwell at the instant you turned off the key, then that one would fire as soon as the key switched off regardless of whether there was still power at the +12 input.
BTW, on shutdown I'm just turning the key back one click. It probably makes a difference because it will still need to be "on" in order for MS to see the engine rotation and trigger the coils. I think.
Is it possible that those with the fuel pop on startup could partially ameliorate the problem with some extra capacitance in their COPs?
And what are the potential downsides, if any, of said extra capacitance? I have not yet installed my 550s but I will be curious to find out if I ever have the startup pop.
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12-16-2009, 10:50 AM
#116
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Dang, sounds like my beautiful hypothesis has been ruined with ugly facts. Wouldn't be the first time. 
Still, shutdown is a bit more "gradual" with no change to my previous configuration other than the COPs. There's an extra ~1/2 second (haven't accurately timed it) of engine rotation that could possibly be useful in clearing out the chambers. If it's not the extra capacitance in the harness, then what other characteristic of the COPs setup is causing this behavior, and can it be exploited to help with the startup pop? The circuit mod is obviously the best solution, I'm just curious why shutdown is so different with the COPs versus stock coils.
Still, shutdown is a bit more "gradual" with no change to my previous configuration other than the COPs. There's an extra ~1/2 second (haven't accurately timed it) of engine rotation that could possibly be useful in clearing out the chambers. If it's not the extra capacitance in the harness, then what other characteristic of the COPs setup is causing this behavior, and can it be exploited to help with the startup pop? The circuit mod is obviously the best solution, I'm just curious why shutdown is so different with the COPs versus stock coils.
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11-07-2010, 02:50 PM
#118
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The rising igniter drive voltage
with increasing primary current that you see is probably due to a current sense resistor scheme in the igniter circuit. (Such an architecture in driving inductive loads is quite common) The scheme accomplishes 2 things - a current limit if dwell is too long, in order to protect the main igniter transistor, and a means for the ECU to be able to sense the primary current by looking at the igniter drive voltage. Presumably some factory ECUs can dynamically adjust dwell time vs. system voltage, akin to having long term fuel trims.
with increasing primary current that you see is probably due to a current sense resistor scheme in the igniter circuit. (Such an architecture in driving inductive loads is quite common) The scheme accomplishes 2 things - a current limit if dwell is too long, in order to protect the main igniter transistor, and a means for the ECU to be able to sense the primary current by looking at the igniter drive voltage. Presumably some factory ECUs can dynamically adjust dwell time vs. system voltage, akin to having long term fuel trims.
So if I understand correctly an OEM ECU might use this feedback to close loop control the dwell? By adjusting the start of the dwell period to attain the desired peak current before firing?
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12-04-2010, 07:07 PM
#120
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Why are the IGN and IAC wires crossed here:
http://miataturbo.wikidot.com/ms2-a
My father and I are working on the mods, and some of the diagrams and instructions scattered throughout the web seem to be incomplete or poorly drawn (Not yours, Joe... the tech diagram is great! Wish the other mods had the same detail and explanation.
http://miataturbo.wikidot.com/ms2-a
My father and I are working on the mods, and some of the diagrams and instructions scattered throughout the web seem to be incomplete or poorly drawn (Not yours, Joe... the tech diagram is great! Wish the other mods had the same detail and explanation.
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