How To Megasquirt Your 2nd Gen RX-7: Parts List

It is best to have all of the following parts on hand before you begin the installation. It is frustrating to get halfway through a job and then find out you need to wait days for the parts to finish.

Megasquirt and Sensors

You can purchase a fully assembled Megasquirt or go with a kit. The kit will be cheaper then the assembled 'Squirt, but it is time consuming to assemble and could be a daunting task if you don't have experience assembling electronics kits.

I have always dealt with DIYAutoTune when purchasing Megasquirt related items. I have found their service to be excellent and their prices fair. While you are of course free to purchase your Megasquirt hardware from any vendor, I will be linking to DIYAutoTune when I refer to Megasquirt stuff.

You have two choices to run the rotary with a Megasquirt, the MSI and the MSII. See the MegaManual for the differences. The long and short of it is that the MSII has better resolution and more features then the MSI. It is also currently being developed while the MSnSE firmware for the MSI is not. The cost of the MSII is somewhat higher then the MSI. The wiring for either ECU is the same, and you can easily upgrade to the MSII if you decided to start with the MSI and then go MSII later on.

You will need one of the following Megasquirts, and the sensors listed for the installation:

While the Megasquirt can use the RX-7s stock ECT/CLT sensor and the stock IAT sensor it requires a hardware mod and, in the case of MSI/Extra, a firmware reflash using EasyTherm. By default all Megasquirts are configured to use the GM sensors. Because of this and the ubiquity of the GM sensors, those are the sensors we are using in this installation. You will need to tap 3/8" NPT threads for each one which will be covered later.

Wideband O2 Sensor

To tune the Megasquirt, allow datalogging and let it run under closed loop, you need an O2 sensor. While a standard narrow band O2 sensor will do the job once the car is tuned and allow you to run closed loop, a wideband is a very important tuning aid and should be considered required. I personally recommend the AEM UEGO Controller. Its 0-5V output will connect directly to the Megasquirt and it is supported in Megatune. There are many other wideband choices but as I cannot cover them all, this writeup deals with using the AEM unit. I have had no issues with the AEM wideband. Another popular choice for Megasquirt users are the Innovate units like the LC-1, LM-1, etc.

2nd VR Sensor Circuit Parts and Pullup Resistors

The stock 2nd gen uses a dual wheel CAS (Crank Angle Sensor) containing a 2 tooth wheel and a 24 tooth wheel to read the position of the engine. The position of each wheel is read by a VR (Variable Reluctance) sensor. As the stock Megasquirt board comes with only one VR sensor conditioner we will need to build a second to handle the 2 tooth wheel (the 24 tooth is read by the existing conditioner). Additionally, 3 pullup resistors need to be added to the status LEDs to drive the ignition coils. You will need the parts listed below in order to build that circuit onto the prototype area of the V3 board. Your best bet for purchasing them is a helpful local electronics store which will probably have everything but the LM1815 in stock. Most communities have an electronics store so check the Yellow Pages to find yours. If you don't have a local shop, Digi-Key carries everything you will ever need and is willing to sell in small quantities. For convenience sake I will put Digi-Key part numbers into the parts list so that you can either order easily, or use them to verify you have the correct parts from the local shop.

E-Fan and BAC Mod Parts

To run the BAC and control an e-fan, two modifications need to be performed. The PWM idle valve modification allows the Megasquirt to control PWM idle valves like our BAC instead of just a fast idle solenoid. The e-fan modification is a standard Megasquirt mod to add an auxiliary output which can be used to activate a relay for a variety of functions. You will require the following parts:

If you are purchasing from DIYAutoTune, both of these modifications are available as cheap "mod kits". The e-fan relay control is available as mk-RelayCtrl and the PWM IAC mod is available as mk-PWMIAC. The mod kits are more expensive then if the parts are bought from DigiKey or your local electronics store, but if you are ordering from DIYAutoTune then it is hard to beat the convenience factor. Note that the IAC mod kit includes the mounting hardware and insulator for the TIP120 power transistor which you will need to mount the transistor to the case. If you are buying the parts separately, you need a mica insulator and plastic screw.

General Wiring Supplies

Finally, you will need the actual wiring supplies to wire this whole setup into the car. Each setup is a bit unique so I am providing a general idea of what you will need. You may need more, you may need less. It all depends on how your vehicle is setup.

The injector connectors specified will fit all S4 injectors as well as the BAC valve. If you have an S5, good luck finding new connectors. Be sure to drop me an email if you do find a source. You'll still need a connector for the BAC though so if you are S5 and using the stock injectors, you will need to order one connector. They are also available from the local auto parts store.

It is important to use adhesive lined heat shrink tubing. Heat shrink with an adhesive lining forms a strong and weatherproof bond between the tubing and the wire. Non-adhesive shrink tube just form a cosmetic and insulating cover but still allows moisture inside. Try to also find heat shrinkable terminals like this one. In addition you will want to have a tube of dielectric grease handy to apply to all exposed electrical connections.

The breaker will be used to connect your Megasquirt related wiring to the vehicle's electrical system. The fuse panel will power all Megasquirt circuits and provide a convenient ground connection. Relays are available at almost all auto parts stores as well as their matching connector.

The shielded cable is used to connect the CAS to the Megasquirt. Shielded cable is absolutely required and don't think you can substitute unshielded because it is cheaper and more easily available. The signal from the CAS is very susceptible to noise so the shielding is very important. In the best case, ignition noise will make the car very hard to tune and will cause it to run poorly. In the worst case, it means a blown engine. Most communities have an electronics store where you can get all your parts, including this cable. If not, try the local music store. Lengths of high quality double shielded microphone cable is available at most good music stores.

Miscellaneous Other Parts

You will also need an assortment of small hardware (nuts, bolts, screws) for mounting relays and the Megasquirt. In addition, about 10 feet of vacuum hose is required to connect the MAP sensor in the 'Squirt to a vacuum source on the engine. There may be a few other supplies necessary for your installation so make sure to read this entire writeup before you begin in case something not mentioned here is required for your car. For example, if you choose to mount your Megasquirt in place of the stock ECU you will need some sheet metal.

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