99 miata ms3x parallel install

[thegrapist]

Hi everyone,

I'm getting an ms3x for my 1999 1.8 miata. It's relatively stock now, but I'll be installing toyota coil on plugs and either an FM turbo kit or a begi s3 turbo kit. The setup will be a parallel install. I'll have the oem ecu handle the idle control, the a/c, I have to figure out what to do with the alternator since the alternator isn't internally regulated and the ecu handles that. For the coil on plugs, I'll be making a circuit that reduces the dwell time. That sounds totally counterproductive since the ms3x can easily handle that, but I'll explain the method to my madness. I'd like to keep the obd2 diagnostic function working as an absolute last line of defense if I grossly neglect something. I'm keeping this car as a summer car for auto x, general enjoyment, and track days. I know it's possible because a guy on the miataturbo boards did it, but he isn't giving me much info. So I'll be using this circuit ( http://forum.miata.net/vb/showthread.php?t=277963 ), so I can safely run the coils at the proper dwell (3.2 ms compared to the stock 5.5ms (toyota coils burn out around 3.5ms), I assume I'll have to set the dwell on the MS3x to 5.5 ms). I want sequential injection also. I'll be using a 2.5 bar map sensor (any reason why I should get a 5 bar sensor over a 2.5 bar sensor? I'll only be running 12 psi on a gt2560R. I don't know if one sensor has better resolution than the other).

So based on all the information this is what I am buying (any suggestions or questions of my methodology would be great for me and my wallet):

http://www.diyautotune.com/catalog/mega ... p-397.html
http://www.diyautotune.com/catalog/mega ... p-434.html
http://www.diyautotune.com/catalog/diyb ... p-411.html
http://www.diyautotune.com/catalog/mega ... -p-32.html
http://www.diyautotune.com/catalog/mega ... -p-47.html
http://www.diyautotune.com/catalog/mega ... p-101.html
http://www.diyautotune.com/catalog/mega ... -p-33.html
http://www.diyautotune.com/catalog/18-m ... p-114.html
http://www.diyautotune.com/catalog/inno ... p-196.html
http://www.diyautotune.com/catalog/lead ... -p-29.html
http://www.diyautotune.com/catalog/mega ... p-168.html
http://www.diyautotune.com/catalog/38-n ... p-107.html
http://www.diyautotune.com/catalog/gm-o ... -p-62.html
http://www.diyautotune.com/catalog/mild ... -p-71.html

an extension harness so I don't have to hack up my factory harness under my car:

http://www.boomslang.us/extension.htm

Any other tips on what I should/should not buy or any sensors/signals should be shared or complications I'll run into?

Thanks for your time and help

[prof315]

Youy can set the dwell to whatever you want. LS coils like 5 to 5.5ms of dwell and they are basically a plug and play with an MS3X. The onboard MS3 2.5 bar sensor will be fine.

[y8s]

I passed OBDII inspection with a parallel engine management system on a turbo miata. And then I gave up because it was more hassle than removing parts every 2 years.

Maybe I was the one you're talking about on miataturbo?

If you truly want the easiest swap between OBDII and megasquirt, here is what I'd suggest:

Run staged injection and keep the stock coils. Then a week before your inspection, wire the wastegate open and plug the ECU connector back into the stock ECU. The car wont be perfect and you'll have to be gentle on the throttle to avoid boosting without enough fuel.

The reason you can't pass with the MS installed is this: the stock ECU controls the fuel to the engine and needs to have 100% control over AFR. It is not as simple as saying "My wideband says idle is at 14.7 so I am good". The ECU is very precise and knows if your narrowband sensor is drifting and will adjust fuel to account for that drift. If it doesn't sense a change in the fueling (essentially it keeps track of how much time the narrowband sensor stays "rich" and "lean" and uses that to determine rough AFR), it will continue to add or subtract fuel until it maxes out the short term trim and throws a code.

When the MS is controlling fuel, there's a disconnect between what the stock ECU is commanding and what the fuel delivery is from the Megasquirt. The stock ECU will learn that it is not truly closed loop and give you trouble.

And that's on top of all the other hassles like air flow meters and other sensors that have to be either properly shared or duplicated.

[muythaibxr]

Keep in mind also that our stance is that the MS is not to be used on emissions controlled vehicles. Off-road use only.

Thanks,

Ken

[thegrapist]

then I gave up because it was more hassle than removing parts every 2 years.

Maybe I was the one you're talking about on miataturbo?

If you truly want the easiest swap between OBDII and megasquirt, here is what I'd suggest:

Run staged injection and keep the stock coils. Then a week before your inspection, wire the wastegate open and plug the ECU connector back into the stock ECU. The car wont be perfect and you'll have to be gentle on the throttle to avoid boosting without enough fuel.

the stock ECU controls the fuel to the engine and needs to have 100% control over AFR. It is not as simple as saying "My wideband says idle is at 14.7 so I am good". The ECU is very precise and knows if your narrowband sensor is drifting and will adjust fuel to account for that drift. If it doesn't sense a change in the fueling (essentially it keeps track of how much time the narrowband sensor stays "rich" and "lean" and uses that to determine rough AFR), it will continue to add or subtract fuel until it maxes out the short term trim and throws a code.

When the MS is controlling fuel, there's a disconnect between what the stock ECU is commanding and what the fuel delivery is from the Megasquirt. The stock ECU will learn that it is not truly closed loop and give you trouble.

And that's on top of all the other hassles like air flow meters and other sensors that have to be either properly shared or duplicated.

y8s, I appreciate your quick response. You weren't the one I was talking about on miataturbo, but stay awhile so I can pick your brain for a few more questions. I would rather not crank the wg in fear of over-revving the turbo. I'd rather spend the extra 60+ hours with the parallel install and never having to touch it again. I understand the stock ecu will crap it's pants if the afr goes rich or lean and it keeps trimming the fuel and how sensitive a (relatively primitive) ecu can be in triggering cel's. Also what signals are shareable with a simple splice? What signals aren't?

And y8s, will the links I put above be good enough to start building?

Keep in mind also that our stance is that the MS is not to be used on emissions controlled vehicles. Off-road use only.

Thanks,

Ken

Right. This is for educational purposes only. I would like to keep obd2 on and the check engine light off for diagnostic services at the track, if the light goes on when I'm going full on all out, then I should back it off and bring it in the pits.