n00b question about MegaSquirt and OBDII emissions
 

Hey. I'm a long time Mazda owner (323, 626, 626, 626, 3, and Tribute) and looking at my first Miata. It's a 2004 Mazdaspeed with the FM Little Enchilada installed and a MegaSquirt ECU. I live in a county in Tennessee which requires annual emissions testing with OBDII. The seller does not, so he doesn't have to worry about it. He does still have the factory ECU included with the car. I'm trying to figure out how much annual hassle I'd be taking on with this car.

I'l admit to being a total n00b when it comes to turbos and especially ECUs for tuning. I have a general understanding of how both work, but no practical experience with either.

I've found threads here and on a few other forums for emissions testing which discuss running the ECUs in parallel or swapping the ECUs out for the emissions testing. The theory makes sense to me, but the details are eluding me. I haven't seen any actual step-by-step instructions on either approach. I'm pretty sure setting them up in parallel is beyond my skill set (at least at the moment), but what about swapping the ECUs annually for the testing? Is it as simple as disconnecting a wiring harness from the MegaSquirt and plugging it into the factory ECU then driving for 100 miles?

I saw one thread mention needing to open the wastegate, removing the blow off valve, reinstall the MAF, etc.... That seems to me that it would temporarily make the turbo "go away" to the ECU. Would those steps only apply to a base or LS Miata that has been turbo'd? It seems to me that the Mazdaspeed factory ECU should already be expecting these things to be in place, right?

Finally, if it's an easy swap, should I keep the factory ECU on all the time? I won't be racing/tracking/autocrossing the car and don't plan on any crazy tuning. I just want a car for driving some fun back country roads. I know the MegaSquirt gives control over things like the AFM, but can the average person tell a difference between an MSM with the Little Enchilada running a tuned MegaSquirt ECU vs the factory ECU, or is most of the benefit already there just from the Little Enchilada even w/o the MegaSquirt? <<See! I told ya'll I'm a n00b! :)

You ask the most easy/common/simple questions. Take 5 minutes to do some research and you'll find all the answers you need.

A megasquirt is NIGHT AND DAY better than an OEM MSM ecu. Like, I wouldn't even buy a MSM if I couldn't replace the garbage stock ecu.

My last MSM (I had several), I bought the megasquirt for the car before I even bought the car. That's how bad the stock ecu is

ASSuming everything has been done with a minimal amount of hacking, all you should need to do is swap injectors, ecu, front o2, and hook the MAF back up again. MAYBE depending on when the car was done, might need to swap oem IAT back in.

I would suggest ONLY doing this for emissions, as the oem ecu is a horrific piece of garbage and unlikely to drive well with a Little Enchilada (or even in 100% stock condition).

I've been reading posts for days. I've tried to research this and understand it, but every post I find assumes the reader knows SOMETHING about this stuff. I've never owned a turbo, never changed a factory ECU, and don't know anyone personally who has. I see comments left and right like "the stock ECU is garbage" followed by 20 others saying "yep!" with some at least saying things like "the stock ECU runs dangerously lean in certain conditions" followed by someone else who says "it's designed to run that way. It's intentional and OK". I can't seem to find specifics about WHY it's garbage other than it not allowing someone to do custom tuning of their AFM, etc. Given a car set up like I described above, what exactly would a novice notice about one with a MegaSquirt vs one with the stock ECU while driving on public roads, not a track/autocross? Is there noticeably less power? Noticeable turbo lag difference? Sputtering? Engine stalls at speed for seemingly no reason? Difficulty starting in certain conditions? What?

@concealer404, thanks. Why would the injectors need to be changed? I thought the Little Enchilada didn't change those, only the Big Enchilada.

Because it has a standalone ecu on it, and anyone with a brain enough to get rid of the garbage oem ecu probably also put appropriately-sized injectors on the car. :)

Stock ecu has horrible lag and a bi-polar power delivery due to bad AFR control. Is also very prone to bogging. I've seen quite a few Little Enchilada cars be unable to avoid boost/fuel cut as well.

Your car isn't a Little Enchilada car. It's a Big Enchilada, but with a better ecu than they provide.

It bogs, it holds back torque by retarding timing and leaning out afr when the turbo wants to make it, and then "unleashing" the power up top so you get a rush of it just as you're running out of rpm, because the rev limit is also set too low, so you smack into the limiter. It feels gutless down low where you want the guts, and then finally goes up top where the turbo is already running out of breath. Daily driving, this is the most counter-intuitive and frustrating thing ever. there is a MASSIVE torque/power/curve/smoothness difference between a stock MSM and one that has a proper tunable ecu which is also tuned properly on it. Night and day

The whole tune/setup was designed as an afterthought. They never perfected it because the factory burned down after 2 production years after which they just cancelled the car altogether.

Thanks to both of you. That helps a LOT!

Other than the annual swap-a-roo for emissions testing and the stuff every car has to have worked on, should it be a pretty low-maintenance affair or is an MSM as described above going to need constant tuning, adjusting, etc.? I know some guys love getting into the weeds of making adjustments to get that one extra ounce of power, but I don't have the time or desire to get into it at that level. Once the tuning is done in the MegaSquirt ECU, is it all pretty much a set-it-and-forget it thing unless something starts acting up?

If it's tuned well, yes.

That said, if you don't want to tune a car, then i'd suggest not buying a car with a standalone ecu.

Other than the annual swap-a-roo for emissions testing and the stuff every car has to have worked on, should it be a pretty low-maintenance affair or is an MSM as described above going to need constant tuning, adjusting, etc.? I know some guys love getting into the weeds of making adjustments to get that one extra ounce of power, but I don't have the time or desire to get into it at that level. Once the tuning is done in the MegaSquirt ECU, is it all pretty much a set-it-and-forget it thing unless something starts acting up? correct
key words being "proper parts" and "properly set up/tuned"

disagreed.
on a daily basis I tune cars for people who then just drive them and not much else.