How To Megasquirt Your 2nd Gen RX-7: Prerequisites And Requirements

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There are several requirements and prerequisites that must be met before the Megasquirt installation is to take place.

The Car

The Car Must Be In Good Running Condition
Before you start it is important that the car be in proper working order. It should run well on the stock ECU and not have problems like bad sensors or vacuum leaks. It should receive a full tune up, the injectors should be clean and there should be no mechanical issues. Starting with a car that does not run would be considered an advanced installation because it is impossible to know the condition of any of the components. Maybe the coils are bad? Maybe an injector is clogged? The fuel pump may be burned out. Any of these issues can quickly complicate a standalone installation whether it be Megasquirt or any other EMS.

The "Throttle Body Mod" Should Be Applied
This is not a hard and fast rule, but will be beneficial in the end. The tertiary set of throttle plates in the TII is there to smooth throttle transitions. In the NA, it is there to prevent wide open throttle when the engine is cold. As we can now tune the car better then the factory ECU, and no self-respecting driver will floor the car when it is cold, these can be removed. While not part of the throttle body mod, removal of the thermowax and coolant feed to the throttle body is often lumped in. While absolutely a bad idea on a stock ECU street driven car, the whole cold start cam and thermowax is unnecessary with a standalone as the BAC now takes over its functions. You will find a great writeup on performing the throttle body mod at FC3S Pro. Becuase the cold start cam physically nudges the throttle open at low temperatures it can make calibrating the TPS very annoying and it will change TPS calibration. Better to just remove it and allow the BAC to do all the work. The dashpot as well can be removed as the Megasquirt dashpot function will use the BAC to emulate a physical dashpot.

Emissions Equipment Needs To Be Removed
As the Megasquirt is an aftermarket ECU for off road use only, it cannot control the stock emissions equipment. Therefore, an emissions removal must be performed on the vehicle. Rotary Resurrection has a good set of articles on emissions removal for S4 NA, S4 TII, S5 NA and S5 TII. You can also find similar articles by searching the RX-7 Forum. However, no matter what any emissions removal article you may read says, do not remove the BAC valve. This writeup makes full use of the BAC valve for warmup idle, idle regulation and dashpot function. For the record, it is crazy under almost any circumstance to remove the BAC. This is not to say that a Megasquirt controlled car will pollute or cannot pass emissions. Most certainly when tuned properly a catalytic converter can be installed and the car will run clean enough to pass the "sniffer" test. Whether this is legal in your jurisdiction is something you are responsible for knowing.

The BAC Valve Must Be Installed
As I mentioned above, the BAC valve must be present. The stock ECU uses the BAC valve to control engine idle speed and the Megasquirt is no different. We will be modding the 'Squirt to run the BAC valve. It will be used for the fast idle when cold, normal idle regulation when warm, and to electronically replace the mechanical dashpot that was removed with the throttle body mod. If you don't have a BAC valve on the car, go get one and install it.

MS3/MS3-Pro Requires High Impedance Injectors
The injector drivers on MS3X/MS3-Pro cannot handle the current demands of low impedance injectors. Therefore, you need to determine your injector type. Very broadly speaking, all FCs below 87.5 have low impedance injectors, and all above have high impedance injectors. It is easy to recognize a low impedance car by the resistor pack installed under the airbox. If you have this resistor pack it will look something like the below picture:

S4 FC Injector Resistor Pack

This is not the stock location for the resistor pack. It is located actually somewhat under the airbox. It has only been moved in this picture for clarity and to make room for an aftermarket air filter.

If in any doubt as to the type of injectors you have, you can measure them with a an ohmmeter. Low impedance measure about 2 - 4 Ohms, high impedance measure about 10 - 14 Ohms. Make sure to disconnect the injector from the harness to measure it directly and not by back probing the connector.

If you are high impedance then you are good to go. If you are low impedance, you have a decision to make which I will cover later in the parts list.


You Must Have Some Mechanical Ability
You're going to need to know how to work on your car. How to remove and reinstall the intake manifold, how to work with the vacuum system, etc. General mechanical ability is going to be required.

You Are Going To Need Some Electronics Knowledge
Or, at least have access to someone who does. Some versions of the Megasquirt (MS1 and MS2) need to be modified (or built, if you go with a kit!) and of course the whole system needs to be wired in. You need to be comfortable with automotive wiring, know the basic concepts of soldering and making a loom, etc. If you don't have these skills, access to a friend who does is also acceptable. It may just cost you a lot of beer by the time the install is finished...

You Need A Place To Work
A nice place to carry out this project is important not only because you need space, but your mental health depends on it. There is nothing more frustrating then working in a confined area with barely enough room to work, or having to step over disassembled parts. The car will be stationary for at least a few days or more realistically a week. If you choose to assemble your Megasquirt from a kit, you will need a well lighted work bench with a comfortable stool or chair.

<< How To Megasquirt Your 2nd Gen RX-7

How To Megasquirt Your 2nd Gen RX-7
Prerequisites And Requirements
Parts List
Building and/or Modding The Megasquirt MS1/MS2
Modding And Setting Up Megasquirt MS3X
Remove Stock Wiring and ECU
Modify Stock Wiring
Mount The Megasquirt ECU
Install CLT and IAT Sensors
Wire The Megasquirt MS1/MS2 Harness Into The Car
Wire The Megasquirt MS3/MS3-Pro Harness Into The Car
Wire The ECU Panel, Wideband and Fuel Pump
Reassemble The Engine Bay
Programming The ECU (MS1)
Programming The ECU (MS2)
Programming The ECU (MS3X / MS3-Pro)
Starting The Car For The First Time
Basic Tuning
Installation Video and Resources
Parts List >>

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