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MegaSquirt Overview for Newbies

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I'm in the process of installing a MegaSquirt system and found it a bit hard at first to understand the various choices. So below is a brief summary of what I learned and a recommended approach for how to determine the best solution for your application. It is not a tutorial on how to tune with MegaSquirt - there are others with far more experience who are better qualified to write it. It is also not a replacement for the MegaSquirt website http://www.megasquirt.info which is loaded with good information. I would suggest you use this as an overview of the basic selection process and then spend the bulk of your time on the MS website.

 

Keep in mind that MegaSquirt is an “open” project designed to work on any vehicle. The original work was done by 2 guys (Bowling & Grippo) who freely published their designs for the circuit boards as well as their software/firmware. They do not sell anything. To buy a kit, or a finished unit, you need to go to one of several companies that sell them. The MegaSquirt website will take you to their sites. Also, other have taken their code and written their own firmware with new features and enhancements. That’s part of the value of this approach, but it can also make things a bit more confusing.

 

Step 1: Which Main Board?

MegaSquirt is available in several main board configurations. As of this writing, there are 2 choices still available: v2.2 and v3.0. In simple terms, the v3.0 board is a redesign of the earlier v2.2 and is more robust and reliable. For you EE types, it is now a 4 layer board with separate power and ground planes. It also has protection built in for the injector drivers. This means it is a more robust board and also more tolerant of electrical noise and wiring mistakes. But there is nothing wrong with the v2.2 board and if properly installed, it will perform well.

 

In general, even though the v3.0 board is a more expensive, if you are starting from scratch I would recommend that you use this board.

 

Step 2: Which Processor?

The original MegaSquirt board and firmware (code that runs on the board) were written for a Motorola 68HC908 microprocessor. While not a cutting edge device, it has plenty of capability for most FI applications. The default firmware has an 8x8 table for tuning the fuel injection map (not to be confused with MAP which means Manifold Absolute Pressure). Main boards that use this processor are considered to be "MS1".

 

There is a daughter card (meaning a small circuit board that plugs into the main board) available that has a more powerful Motorola MC9S12C64 microprocessor. It also has some additional circuitry that is useful for controlling ignition events (spark). MegaSquirt applications that use this card are called "MSII". See the MegaSquirt website to learn more about the differences.

 

Note: Either processor can be used with either main board. Hence you can configure as a MS1 v3.0, or perhaps a MSII v2.2.

 

Step 3: Which firmware (code)?

Now you need to decide what you want to do with the MegaSquirt. Do you want to:

a) control fuel only?

B) control fuel and spark?

c) control other options (electric fans, idle control, boost for a turbo, NO2, water injection, etc)

 

There are different versions of the firmware available with a variety of features that may or may not be of value for you in your specific application. You can always change firmware after you install, but if you have made some hardware modifications, the new version of the firmware may not handle them the same way, and you might need to get the soldering iron out again. Hence if you can pick the version you want before you start, you have a much better chance of doing your soldering only once.

 

Also, different versions of firmware support different size tables for tuning. The default MS1 code supports a table that is 8x8 meaning it can be tuned for 8 different rpm points and 8 different MAP points (total of 8x8=64 points). For most N/A applications this is sufficient. There is another version called MSnS (MegaSquirt n'Spark) that increases this to 12x12 and offers some other enhancements as well. The MSII processor supports 12x12 tables with the standard code.

 

Step 4: Find a mounting location

The MegaSquirt main board needs to be mounted inside the cabin and NOT in the engine compartment as it's not designed to live in that range of temperatures. A common place in a Z is under one of the seats or mounted on the firewall under the dash on the passenger side (if you don't have AC).

 

Step 5: Build your own "relay board" or use the MegaSquirt one?

While it is possible to connect the sensors directly to the MegaSquirt main board, it's neither easy nor desirable. There is a relay board available that includes relays to control power to the MegaSquirt main board, fuel pump, and also for a fast idle device (won't work for a PWM or Stepper motor type without modifications - the relay can only control a solenoid type). It also contains a terminal strip with screws to make it easier to connect the sensor wires along with the injector wires.

 

But it's not necessary and many people choose to build their own. Look around on this site and you'll find a wide array of approaches. I am using the relay board mounted on a roughly 12" x 12" masonite board along with the main board, with a separate terminal strip to connect all the power and ground wires.

 

Note: It's a good idea to use a single ground point for everything, especially if you are using a wide band O2 sensor which has its own controller. Also, you should solder any splices in the wires for the signals (sensor, O2, etc) instead of crimping. It's not required for the main power connections, but won't hurt if you do.

 

Step 6: Decide on hardware mods

Because of the flexibility of the design of MegaSquirt, it's easy to modify it to do other things. For example, you can control an electric fan with a spare output on the main board. However, the output does not have enough current capability to directly control the fan, or even a relay. So you have to add a special transistor which acts as a switch with enough current capability to safely control the relay. On the v3.0 main board there is an unused proto area where you can add this. The website has circuits showing how to connect things, and some of the vendors will sell you the kits.

 

The key is that in some cases the mods will require the removal of a few components from the boards. If you are building the kit yourself, it's better to just not add the component in the first place. While the circuit board material is robust, if you're not experienced with desoldering, it's possible to damage the board or components around it with too much heat. Knowing in advance what you're going to want to modify is a much better way to go.

 

Step 7: Choose an O2 sensor

If you're merely replacing an existing stock FI system on a N/A engine that's otherwise stock, it probably has a narrow band sensor and you can easily stay with that and save some $$$. If you're going turbo, or doing performance enhancements on a N/A engine, then you should probably go wideband. The main issue is that a narrow band can only tell if the mixture is lean or rich, but not how much. A wideband lets you know the actual AFR (Air Fuel Ratio) which makes tuning easier. Also, some of the firmware versions can support a closed loop mode that can “self tune” with a wideband O2 sensor under some conditions (less than 70% full throttle).

 

This really doesn't affect your choice of MegaSquirt components, but you do need to decide as part of your overall plan.

 

Step 8: Reuse existing temperature sensors or replace?

The MegaSquirt system is designed to be able to work with just about any temperature sensors (you need at least 2: one for the coolant, and one for the intake air). If you already have sensors on your engine and want to reuse them, you can. You will need to calibrate them so the main board knows how to interpret their signals and correlate that to the actual temperature. There is software available to make this easier.

 

You can also replace them with generic GM units in which case you won’t need to calibrate – MegaSquirt is preset to work with them. In my case, since I was converting a carb car without an air temp sensor, I decided to just buy the new GM sensors.

 

Step 9: Choose your tuning software

The settings on the MegaSquirt main board must be set by a program running on a PC. The default application for this is called MegaTune and it runs on Windows. There are others out there, including some that run on other operating systems such as Linux and MAC.

 

Note: you only need to use the tuning software while you're tuning. Once you finish, you don't need the computer any more.

 

Note: the standard interface between the MegaSquirt main board and the computer is a 9 pin serial cable (used to be called RS232). This port has been replaced with a USB port on most newer computers so you will need to get a USB to RS232 converter. Most of the sources of the MegaSquirt kits also sell these, and it's a good idea to go with one they recommend to avoid having issues on the PC getting it to talk to the MegaSquirt main board.

 

Summary:

Obviously there is a lot more to planning the install, including wiring sizes, wiring routing, upgrading injectors, sensor locations, and of course, the actual tuning process. Much of that is already covered in this forum and also on the MegaSquirt website so I won’t include it here.

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Something that has bothered me for a long time now is that when I wrote the install sticky guide MSnS_Extra code didn't even exist, neither did the v3.0 board or MSII. I have kind of been hoping that someone would do a better writeup maybe just cutting and pasting a few sections from my original stuff and then we could trash the old writeup. Maybe some people worry about stepping on toes or something else, but I am here to tell you that I am all about helping out and it doesn't bother me one bit if we replace that original install guide. No hard feelings or any of that, the problem is that I can't really do it justice because I have not used a V3.0 board, I don't even have a z car anymore, I haven't used MSII at all.

 

 

So, anyone that wants to put together a better writeup feel free to use any part of the original in any manner you want, even if it is to say this is a bad way to do things.

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Just a little note,

 

MAP stands for Manifold Absolute Pressure. Not air pressure.

 

It is called absolute pressure because it is referenced to a absolute vacuum. The 2.5 bar sensor inside the MS units is good to only 1.5 bar boost pressure in a turbo application. 1.5 bar boost + 1 bar atmosferic pressure is 2.5 bar sensor.

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Something that has bothered me for a long time now is that when I wrote the install sticky guide MSnS_Extra code didn't even exist, neither did the v3.0 board or MSII. I have kind of been hoping that someone would do a better writeup maybe just cutting and pasting a few sections from my original stuff and then we could trash the old writeup. Maybe some people worry about stepping on toes or something else, but I am here to tell you that I am all about helping out and it doesn't bother me one bit if we replace that original install guide. No hard feelings or any of that, the problem is that I can't really do it justice because I have not used a V3.0 board, I don't even have a z car anymore, I haven't used MSII at all.

 

 

So, anyone that wants to put together a better writeup feel free to use any part of the original in any manner you want, even if it is to say this is a bad way to do things.

Mobeythevan, I appreciate what you said and your desire to put good information out on this forum. I had thought about trying to take this further, but in the end I decided not to because:

- There are so many permutations and variables that it would be impractical (and too long to read) to discuss all of them.

- Unlike mechanical things (like Jon's great summary of diffy's for S30s) the MegaSquirt world is constantly evolving because of its open nature - especially with regard to the firmware and tuning software.

- The MegaSquirt website has a TON of information, including forums, and although they aren't as tightly run as this site, a little searching and browsing yields lot's of good information.

 

I think it's safe to say that converting to MegaSquirt isn't rocket science, but none the less, it does require a lot of research to be done well, just like every other conversion on our Zs.

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I'm curious about MS. First off if I try and do it and mess up is there anyone to take it to fix? And what does the tuning software look like, do you just fill in the blanks for like injectors or tb size or something ? Also I'm sure i can find this by searching but will ask here anyways at a CA smog station if they don't see the MS then they can't fail you right. They don't need to plug in or anything ?

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I can't help you with your question about the CA smog stations. As for fixing an MS board, there are people to whom you can send it and they will diagnose and fix it for a fee. If you're not already familiar with building electronic circuit boards, you might be better off buying one already assembled.

 

As for tuning, I'm just getting started with it. In theory, you are correct, you just enter values in the boxes. In practice, knowing what values to start with for your particular engine, and how to adjust them to improve things, is the issue. I'm actually enjoying the learning process, but it takes quite a bit of time.

 

Going into this project I expected that I would be able to start with the settings (msq file) from someone with a similar setup and then just fine tune from there. In reality, that hasn't been successful. I've had to find a little here, and a little there from different people to amass most of what I need. If you know someone already experienced with megasquirt, that would make things go a lot faster I think.

 

I'm not trying to discourage you from this, but suggest that you be fully aware of what's involved if you go this route. I will say that so far, I have no regrets at all for having gone down this path.

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I would advise people to purchase a stimuator board for their MS ECU. It can save so much time diagnosing the problem. That way people on the forums trying to help, will have a lot more information to work with.
As a general statement I agree. But if you have good experience soldering and have an EE-type background, then you probably can get by without it - I did, but you're trading time for saving ~$50.

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Guest aircoolsteve

hi. i'm in the latter stages of putting a plan together for a MS system for my progect. the thing is, i run a Mac and not a PC.

will i have to puchase or borrow a PC to progame the MS system or will i be able to use my Mac?

many thanks. steve

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I think you could get by with an old P3 or old P4 laptop that has win XP on it just to tune . They can be found for 100$

That's the route I took and it worked great. I don't have to worry if the laptop is dropped or stolen as I would if it was my main laptop.

 

But if you want to use a different OS, check out the MS forums.

 

http://www.msefi.com/index.php?c=8&sid=8131512d1ca97111425b3f4546af208b

 

I believe megatunix supports Linux and hence maybe mac osX. But check to be sure.

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My old dog, P3, dell, laptop, works great for surfing the web, email, and tuning. The serial port has proven very valuable. It runs XP and is the most stable PC that I have. It even gets 4.5 actual hours out of the $49 ebay "dell" battery.

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Guest aircoolsteve

many thanks for all the info one and all. ought to be able to pick up a laptop ok on ebay and just use it for that perpose. cheers. steve

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hey guys, i have been searching for what feels like forever! where are the "main relay" and the Fuel pump relay"s located in an 87' 300zx turbo? any one here done a MSq-II i one before?

 

Just trying to get this stuff straight.

 

thanks guys,

Cody J.

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Guest capyupju

Out of the many posts, this one attract my attention.

I believe it is possible for anyone to participate.

Excellent ! I like it very much.

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Can you purchase an all options included prebuilt board and use what you have and add fans etc as you go or does everything have to recieve a signal in order for the whole thing to work?

 

DIYAutoTune.com sells prebuilt and complete boards.

 

And no, you don't have to have everything working and receiving a signal for the complete unit to function.

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just a quick question. the Stock AFM tells the ECU the amount of air that is coming through. once you use megasquirt, the AFM is removed. What tells megasquirt the amount of air that comes in? the Manifold Absolute Pressor (MAP) sensor?

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just a quick question. the Stock AFM tells the ECU the amount of air that is coming through. once you use megasquirt, the AFM is removed. What tells megasquirt the amount of air that comes in? the Manifold Absolute Pressor (MAP) sensor?

 

Correct. It has a table of how much fuel to inject based on MAP sensor readings and RPM.

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Hopefully this is a fairly simple question to answer, and I wasn't sure it needed it's own thread.

 

I've got a megasquirt 2.2 sitting here unassembled. I'm planning on running ms'n's on it. I know this means I'll be sacrificing FIDLE, but what if any hardware modifications do I need to make from the instructions on building a stock unit as far as the mainboard and relay board?

 

I'm not planning on running EDIS, so I'll be keeping a distributor since that seems like that keeps things simpler (unless I'm wrong).

 

If there aren't any hardware modifications, then I can just build it up the way the instructions say, and then once I've got it done I just flash it with the new ms'n's code instead before it goes in the car, correct?

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