Run hotter plugs? :-)

Is it always one cylinder?

 

Did it again today.

No, before the mod i'd sometimes foul 2 and one time I swear I started it on one cyl. Sucks.

It is 98% better after Joe's new spark circuit. I just still dont feel like I solved the root issue.

 

It sounds like leaky injectors? Perhaps running the motor a bit before sparking would help

 

havent i been saying that for a year now about wayne's car? :P

 

Lol, yes you have. My TPS isn't working for some reason right now so I cant do flood clear. I still feel like even if I flood cleared it and it never popped again, I should still fix the leaky injectors.

 

nah, we love band-aids here.

 

Can you just clean it?

 

The Injectors? They've got less than 4k miles since they were cleaned and flow-tested.

 

Flood clear won't help with the popping... The fuel is already there, and it'll probably still spark even in clear mode.

 

I think scotts suggestion a while back was to flood clear after shutting the car down before I get out. That way I could see if it was the injectors leaking over time, or just a little bit left in there after shutdown.

 

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.

 

I've been doing this minus flooring the pedal for a long time now and hasn't seemed to help. I'll start doing it while flooring it and see if it helps.

 

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.

 

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.

 

While that's possible, the coils aren't going to fire unless something is triggering them.

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.



Assuming you're taking the power for your MS from the stock white/red wire, it only receives power in the "Run" position of the key. So one click back, which puts you into the "Acc" position, would kill power to the ECU.


I hate saying things like "never" or "impossible", but I can't fathom any way in which adding parallel capacitance on the power feed to the coils would affect their power-on behavior, unless the ESR of the caps was so low that they were dragging down the power line. (This is almost impossible to fathom.)


No downside that I can think of.

 

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.

 

good mod.! thanks Joe.

I have a year with random "poping" but not any more.

 

Has anyone decapped the OEM module to confirm this?

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?

 

LOL at the Beatles background.

 

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.