xJyzr

Hello everyone, I saw a similar thread about this topic from a few years back but wanted to see if there were any new developments? My issue is simply that I purchased a second hand Megasquirt off good ole Facebook market place that was advertised as a 90-93 but it’s a 94-95. Is it possible to run the 94-95 without having to change much or do I just have to buy a new 90-93 and try to sell the other one?

Z_WAAAAAZ

I'm not sure if it's fully possible to run that ecu on your car, there's a handful of guys on here that can answer that question for sure.

What I can tell you is that if it is possible, it's gonna be a **** ton of work. Wiring schematics for the two are way different. Maybe someone can elaborate/check me on this response but if it is possible, the amount of rewiring involved would drive me to sell the 94/95 unit and buy a 90-93.

xJyzr

Thank you for the response! I was hoping that wouldn't be the case but never hurts to ask and see. On the other forum (https://www.miataturbo.net/megasquir...-1990-a-76237/) OP said he was able to run the car on a 94-95 with minor issues of idling and fuel but thats not exactly something I'd want to delve into without at least knowledge that it is possible.

Z_WAAAAAZ

Yeah, no sweat dude! Again, take my response with a grain of salt.

Based on my knowledge base, the main concerns with mating the 94/95 ECU to a '90 chassis would be entirely with adapting the 94/95 ECU wiring harness to the wiring harness currently in the car. Once you spliced all the wires in the ECU harness to where they need to go in the car's wiring harness, everything should function like it would with the 90-93 ECU. Fueling and idle concerns would be addressed by the tune.

curly

iTrader: (25)

The harnesses are actually identical, just slightly different pinout. IIRC, MSlabs units were even 90-95 based, with just different jumper locations between 90-93 and 94-95.

Look at the two wiring diagrams and re-pin what’s different. The 94-95 will have sequential injection, but you should be wiring that anyways. Same with VTPS, etc. again, compare diagrams, but IIRC, grounds, 12v, injectors, and quite a few other I/O’s are identical.

xJyzr

So theoretically it wouldn't be too much work to match up the pinouts on the megasquirt to the wiring harness but the ecu should power the car without any changes? If so then the mentioned thread from before was right.

curly

iTrader: (25)

Correct. Pop the little tab on either side and hinge it away, then take a very small pick, I use ground down pocket screw drivers, and pry the locking tab up while you pull the pin out. Swap around what doesn't match up and it'll work.

Again, you want to look up proper wiring diagrams, but you're looking for the differences between these two:

Looks like FP, fan, and AC fan triggers move, along with 5v ref.

xJyzr

Thank you, I'm not too well versed on rewiring stuff like this but I will attempt to make it work as even though it's only been a few days, I've had zero luck on trying to sell the 94-95 ecu. I appreciate the help!