How To Megasquirt Your 2nd Gen RX-7

Home > RX-7 > Tech/Mods > Mods > Megasquirt > How To Megasquirt Your 2nd Gen RX-7


The Megasquirt has become a very popular ECU for the RX-7. It is an extremely capable and inexpensive DIY ECU. However as the Megamanual says, "Experimental means that you are responsible for sorting out some details of your fuel injection that are specific to your application. Do-it-yourself means that you save money by assembling it yourself with a few basic tools and comprehensive instructions.". This means that out of the box, the Megasquirt requires some modifications to run the rotary. Almost all applications require one or two modifications to the 'Squirt but as the rotary has a unique ignition system, it is a bit more involved then most installations.

Don't let this deter you, however. Behind the Megasquirt is a huge community of users that are more then willing to help out. Indeed, as the Megasquirt is an open-source community project, it only exists because of those people who have put their time and knowledge into creating it. As it turns out, Ken, one of the authors of the Megasquirt and Spark Extra (MS1 Extra / MSnSE) firmware, is an avid RX-7 enthusiast. And it is mainly due to his work that we have full rotary ignition capability in this firmware as well as the code necessary to run our staged injection. Ken, posting on the RX-7 forum as muythaibxr has created an excellent FAQ for MS1 and another FAQ for MSII. I've helped a little with the MS1 FAQ. However, the one disadvantage about the community approach is that information, even with the FAQs, can be a bit splintered and spread across various parts of the Internet. This is the primary reason I've decided to do this writeup. Nowhere has existed a complete 2nd Gen RX-7 Megasquirt write up until now.

A Word Of Warning

Before we go any further, it is important to reinforce that the Megasquirt is in every way a Do It Yourself ECU. This means that you build the ECU. You modify it to work with the rotary, and you are in charge of wiring it up to make it work in your car.

If you have never soldered before or have no experience in basic electronics, then the Megasquirt may not be for you. While pre-assembled Megasquirts are available (we will cover this later) they still require modifications to work with the rotary. You'll need to add a second reluctor conditioner (we'll cover this) and set up the status LEDs as ignition outputs. While not overly complicated if you can read a schematic, being an electronics novice will make things much more difficult.

Once the Megasquirt is installed, it must be tuned. A significant stumbling block for first time tuners is simply getting the vehicle to start. With no frame of reference, it is difficult to guess how much fuel the engine needs when starting with a blank map. And I don't think I need to mention how disastrous it can be to tune a rotary too lean.

Finally, the Megasquirt is not legal for road use on pollution controlled vehicles. Standalones are for off road use only.

Types Of Megasquirt

The Megasquirt is not a single ECU, it is a collection of them all based upon a common ground. There are actually 5 (well, 6 if you consider the Sequencer but it will be a long time before we see it in real life) versions of the Megasquirt. Version 1.01 is the original 'Squirt and no longer available. It's highly unlikely you will ever see one. The version 2.2 has some improvements over V1.01 but is no longer being produced. They are still available from the vendors and can be modified for rotary use, but the version 3 is a much better choice. The V3 is a vastly improved design over the V2.2. It is designed to run the MSnSE firmware and offers the option of multiple ignition inputs, a flyback circuit and a host of other improvements. Then there is the V3.57. The V3.57 is basically the same as the V3, but uses surface mount components and has a few other minor improvements. Finally, there is the Microsquirt which is made with a small surface mount board and sealed into a weather tight enclosure (and is also available as a bare board).

Now, all of the boards with the exception of the Microsquirt have a choice of two processors. The MS1 is the original CPU and is a 68HC908. The MSII consists of a much faster MC9S12C64 processor mounted on a daughter card.

To complicate things further, there are many different firmware versions available for different purposes. MS1 chips have one set of firmwares, MSII chips have another.

Because of all these differences, we will only deal with two configurations in this writeup; the MS1 CPU on the V3 board, or the MSII CPU on the V3 board. MSI will run the MSnSE (MS1/Extra) firmware, MSII will run the MS2/Extra firmware.

Configurations Covered In This Writeup

Because there are so many possible configurations of the Megasquirt, this document will only deal with one specific way of installing the 'Squirt. It would be difficult, if not impossible, to cover all scenarios. So we will cover the following setup:

Necessary Modifications To The Megasquirt

We'll cover this in detail a little later on, but there two modifications that must be done to the Megasquirt in order to run the ignition system on the 2nd gen RX-7. First, a second variable reluctor (VR) circuit must be built to allow use of the stock CAS. Second, pullup resistors must be added to the three status LEDs to drive the coils. In addition, we will be adding a simple circuit to control an electric fan, and we will also apply the PWM IAC mod to control the RX-7s BAC idle valve.

Getting Down To Business

The rest of this writeup is split up into sections to make reading a bit easier.

<< Previous

How To Megasquirt Your 2nd Gen RX-7
Prerequisites And Requirements
Parts List
Building and/or Modding The Megasquirt
Remove Stock Wiring and ECU
Modify Stock Wiring
Mount The Megasquirt ECU
Install CLT and IAT Sensors
Wire The Megasquirt Harness Into The Car
Wire The ECU Panel, Wideband and Fuel Pump
Reassemble The Engine Bay
Programming The ECU (MS1)
Programming The ECU (MS2)
Starting The Car For The First Time
Basic Tuning
Prerequisites And Requirements >>

Back To Mods Page | Mail Me | Search