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Discussion Starter #1
I'm getting ready to get back into my miata again. My new objective for the car is to get it back on the road legally again. The biggest hurtle is that it is a '96 and in my area that means that I have to pass OBD2 testing. I currently have a vintage but very functional link ecu from flyin miata in the car which has nothing at all in the way of OBD2 support.

I think the solution to getting the car to plug in and report good is going to be a stock ecu in parallel to my link. My primary concerns are figuring out how sensitive the stock ecu is to what is actually attached to it, and how to fake the maf signal.

Wiring from the sensors is fairly straight forward, but I'm not sure if I will need to put any diodes or resistors to keep things running properly. I'm also not sure if the stock ecu will throw any codes if the injectors are not hooked up.

The big question is how to deal with the maf. My car runs on a map system and I'm not planning on changing that. That means that I somehow need to duplicate the signal that the ecu will expect to see so that it does not become confused. Does anyone know what voltage range the maf signal is? Also, any thoughts on how the stock ecu will interpret a flatline maf signal while the engine is off doing its own thing?

My theory is that the stock ecu is probably not smart enough to know that something is up when the engine rpm's and tps are changing but the maf signal is flat - after all since it will be reading the o2 sensors it "knows" that the engine is running properly.

Anyone ever done this and have any comments or suggestions?
 

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http://www.elektor.com/magazines/2010/june/obd2-mini-simulator.1352041.lynkx
as long as this is attached and looks factory under the dash and the check engine light is on and shut off with car running like a normal car would this will work way better and wont compromise your wiring. its not like your setup is legal anyway. if you have a scan tool you can plug it in and check if it all looks normal before going to the e-lane.
 

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Discussion Starter #3
I did some searching on simulators and what I've turned up suggests that they might not be the best idea. The problem comes from knowing what all the testing computers look for. If they just scan for codes and CEL, the simulator would do fine. If they get fancier and check signals for rpm, vin, or any of the other stuff that can go in there, they will not report correctly.

I think I'll probably go ahead with the parallel ecu idea just to be safe. Heck, with that in place I don't even think I'm doing anything illegal.
 

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i know that they dont show any engine vitals but I have used one before and passed the only thing illinois systems are checking for is codes and if the tests are completed
 

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In for more info. I have a 96 as well that I have megasquirted and also am looking into the simulators. This should be a good read if more people can chime in on what they have done.
 

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Discussion Starter #8
That's a great example crispspeeed! Would you mind posting a little about what was done to make it work? I'm interested in exactly what I will have to simulate and what can be ignored when I hook everything in parallel.
 

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That's a great example crispspeeed! Would you mind posting a little about what was done to make it work? I'm interested in exactly what I will have to simulate and what can be ignored when I hook everything in parallel.
With the above setup the only thing the factory ecu can have a CEL for would be the injectors which can be simulated easily but I don't believe the early Miata ecu had any codes for the injector circuit but I may be wrong. The application above never had any CEL codes until I disconnected the airflow meter LOL!
 

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Discussion Starter #10
until I disconnected the airflow meter LOL!
:( That's what I was worried about. My car is set up with a MAP sensor and no airflow meter. I may have to get my hands on a stock 1.8 car for a bit and see what kind of signal the meter sends off. If I can figure out the voltage range, I ought to be able to simulate it.
 

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The main hurdle these days is the MAF. Everything else will work as usual with say a megasquirt in parallel. it just has to run the car similar to how the factory computer would, the main things that set off my CEL are: Super rich AFR, Misses, missing o2 sensors (lol), no MAF. People have tried bypassing the MAF but its really hard to trick the stock computer because no one really knows how it works. From what I know and have read:
It contains a intake air temp sensor, and a mass airflow sensor. The IAT part is easy to trick, with a simple resistor you can make the computer think it like 70* all the time. The MAF on the other hand looks for a different type of signal that is a lot harder to reproduce correctly. So the best way is to reconnect it before smog haha.

There is no injector code/CEL. If your: afr stays between 14.0 and 16.0 all the time,your o2 sensors are plugged in and functioning, you have a working cat, and you made your parallel harness correctly, you should get any CELs and should be able to pass emissions!
As far as harness goes, make sure to share the right connections (like coolant, CAS, etc) and clip the ones ms or aftermarket ecm will be controlling (INJ, Spark).

EDIT:
In post above I see your setup and goal

Not to sound like a debbie downer but I doubt you'll be able to simulate the MAF signal unless you have the equipment to test one and skill/knowledge of microelectronics to build something capable of emitting the correct PWM for the computer not to throw a code.

Not only does the miatas MAF sense mass air flow, it also calculates it, then sends the calculated airflow to the computer as a pulse :(
 
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