MegaStim:
Ok, I built the board myself and HIGHLY recommend buying the MegaStim if you are planning on building it yourself. That is HIGHLY like Really Really! It allows you to test your board as you build it so that you can make sure you are not messing up. Basically like a checkpoint in a video game. If you die...you start over from the last check point. It took me over 12 hours to build the Stim and MS Boards...but I was a soldering rookie. It also lets you do all your initial set up before you wire it into the car and will give you a chance to play with and learn the MegaTune software. It eats 9V batteries like a SOAB, so keep that in mind. You will commonly get a message like, low battery cannot burn. Do you want to try anyway? Always do. If it asks you twice, that means the battery is toast. Also, if it gets too low, your computer will start beeping at you. This is the MS resetting and it is not good for it so try not to let the battery get too low.
Relay Boards:
Basically they offered this because a lot of people wired things up wrong on their car and fried the MS. I don't think that they are needed, but I was extremely careful in wiring mine up and made sure that I was connecting the right wires and they were high quality connections with no chance of shorts. So, It all depends on how focused you can be. If you are not detail oriented...you might want to buy the relay board but honestly I think it is a waste of money.
Assembly:
There are a few decisions that you have to make while assembling the board that require you to know things that aren't common knowledge. A few things I learned while building the board for example were.
-Our Idle Air Control (IAC) is a Pulse Width Modulation (PWM) unit, not a solenoid or a stepper motor. You can set it at different duty cycles for different temperature values in MS.
-The Mx-3 was ahead of its time in that it came with sequential fuel injection. This just means that each injector fired independently and exactly when it needed to in the engine cycle. Pretty cool, even though it is not hugely important. What is important is that MegaSquirt will not support Sequential Fuel Injection without modification, so to use MS you are going to be using Batch fuel injection, usually one bank at a time. Some people stagger their injectors (1,4,6 on one wire and 2,3,5 on the other wire.) as they say it keeps the fuel pressure up in the rail. I don’t think it matters one bit since both fuel rails run from the same fuel line and through the same FPR. Either way, it doesn’t matter.
-Our fuel injectors are High Impedance injectors and there are instructions in the MegaManual about how to build and configure your MegaSquirt to run them. There are 2 settings on the Injector Characteristics page that you have to change. Your car will not run without these settings done correctly…I can personally attest to that. HAHA!
-On the V3 board, it is best to set up both the Hall and the VR (Variable Reluctor) options. You use a jumper to select which one you want to use depending on where you are getting your tach signal. If you are using your stock distributor like I am. You can simply patch into the tach signal that runs from the Hall sensor in the disty. A lot of people end up ditching the distributor all together in favor of external coils or coil packs. If you do this, you will need to use the Crank Angle Sensor to get your tach signal and you will end up having to grind one of the teeth off of your Crank Pully to tell the MS where cyl. #1 is. Not just any tooth…look on ProbeTalk for the how to.
Wiring:
Wiring it up is a piece of cake if you are piggybacking. I would still recommend that you do it in a way that you can easily go back to using your current ECU so that you can drive it if you encounter any problems. I used spade connectors on the wires that I cut from the engine harness. All the other wires, I just taped into with quick taps from Home Depot. If you are going to be running MS stand alone, a clean way I thought of to do it would be to get your hands on the female ports of an ECU, and wire the corresponding pins to the MS…then all you would need to do is plug the stock wiring harness into those female ports and thus right to your MS. This is of course only if you ever want to be able to put a stock ECU back in. If not, just make your own wiring harness and run it all the way to the connectors on your sensors. Attached is a wiring diagram for how to wire the MS into the wiring harness. I modified it from a Probe application to match the 93 Mx-3 GS wiring. Even if you have a different year V6 the ECU pins should still be the same, but you should check to make sure.
Tuning:
I will let you know when I know. I have tried a few maps that I have found on the net, but none of them seem quite right.
