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

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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. Typically this means having extra wire, extra connectors, plenty of solder and even an extra soldering iron handy.

MS1/MS2 Megasquirts require a different set of parts than MS3X/MS3-Pro and the differences are covered below. As mentioned previously, MS1/MS2 involves more DIY work than MS3X/MS3-Pro and the parts lists reflect that.

Megasquirt

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.

First on the list is the Megasquirt itself and what you need to buy depends on the version you have chosen.

Megasquirt 1 / Megasquirt 2

Megasquirt 3

Your best bet for MS3X is to buy it as an assembled unit. It's going to be cheaper vs. buying all the components and assembling it yourself. I've only included the discrete MS3X components to show what is included in an MS3X unit compared to an MS1/MS2. Yes, you can upgrade an MS1/MS2 to MS3X using the components in the above table but that is beyond this writeup and not covered here. MS3X requires two wiring harnesses, one for the main board which connects to the majority of the sensors, and one on the MS3X expander board consisting primarily of the sequential fuel/ignition outputs, aux outputs, and a few aux inputs.

MS3-Pro

MS3-Pro uses two wiring harnesses like MS3X but they use Ampseal connectors and many of the inputs/outputs are named more generically. MS3-Pro also requires an external MAP sensor as there is no sensor on board like the MS1/MS2/MS3. These sensors are the fairly standard GM 3 bar MAP unit and available at any auto parts store but if you are ordering your MS3-Pro from DIYAutoTune, it may as well be ordered at the same time.

Sensors and Harness (All Megasquirts)

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 data logging 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 (though only at 14.7:1 so in no way do I recommend this approach), 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/TunerStudio/MegaLogViewer. 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.

MS3X/MS3-Pro Fuel Injector Impedance Options

As mentioned in Prerequisites and Requirements, MS3/MS3-Pro ECUs require the use of high impedance injectors. If you have determined your injectors are high impedance, you are good to go.

If you have low impedance injectors, you have several options, the most common of which I will present here.

Option the first is to simply swap with high impedance injectors. All FCs after 87.5 are high impedance (though check to make sure before purchase as you never know, someone may have swapped injectors) and swap directly in on the older cars with only a change in connector (the tab may need to be filed down). So you can purchase a set of high impedance injectors from a later model year FC. Then have them cleaned and tested at the local injection shop.

If you have an NA FC, the Mazda RX-8 (2004 - 2008) 6 port injector is a great choice. They are 450CC, high impedance, and a modern disc design (as opposed to the old pintle style). They are Denso part #N3H313250A 195500-4450 and available at most auto parts stores as well as Mazda. They drop right into the FC but you need to use the appropriate Denso connector. TII owners (550CC injectors) can use the Denso 195500-4460 RX-8 (4 port secondary I believe) injector. It's 540CC which is close enough to the stock 550CC for stock turbo use.

Option number two is to a resistor in series with each injector. This is the approach preferred by OEMs when running low impedance injectors on an ECU which can only handle high (and indeed what Mazda did on the FC). You will need 4 resistors, one for each injector. The value is not massively critical as long as it raises the total resistance enough to prevent excess current through the MS3X/MS3-Pro drivers. I buy 6 Ohm 10 Watt metal cased power resistors from my local electronic store however if you don't have such a store, then DigiKey has 7.5 Ohm 25 W units in stock almost always as part 825F7R5E-ND. The disadvantage of series resistors is that they ever so slightly slow injector opening times and require slightly more PWM time to open. In reality, with the pulsewidths we run at idle and in the midrange, this won't make a difference. If you have a perfectly good set of cleaned and tested low impedance injectors or aftermarket larger injectors, then resistors are a good choice.

These resistors will need to be mounted to the MegaSquirt case or ECU bracket. If they are placed in the engine bay then they must be mounted in a sealed box.

2nd VR Sensor Circuit Parts and Pullup Resistors (MS1/MS2 Only)

If you are installing MS1/MS2, then you will need the following parts. MS3 users need not apply as MS3X/MS3-Pro already includes the necessary hardware.

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 (MS1/MS2 Only)

If you are installing MS1/MS2, then you will need the following parts. MS3 users need not apply as MS3X/MS3-Pro already includes the necessary hardware.

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.

Again, the 2nd VR, pullup resistors, PWM idle and e-fan/relay control mods only apply to Megasquirt 1 and Megasquirt 2 users. All of this hardware is already included on the V3.57 board and Expander board used by MS3X and on the MS3-Pro.

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.

Note the different connectors needed for the square style S4 injector connectors vs. the round style S5 connectors. The BAC connector matches the injector connectors generally so if you have an S5 your BAC connector will be round, for S4, square. In many cases thee connectors are available from the local auto parts store though it may take some looking through the catalogue if they don't have a listing for the RX-7.

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. MS3 and MS1/MS2 have different requirements. MS1 and MS2 users will run a single 4 conductor shielded cable to the main board. MS3X users will have two shielded cables each having 2 conductors. One runs to the main board and is included on the Megasquirt harness. Another runs to the MS3X expander board and may or may not be included on the MS3X harness. Some MS3X harnesses have only an unshielded wire to their VR ("CAM") input. Some have the much better shielded pair. At this point all MS3X harnesses should have the shielded cable but it does vary between vendors and when your harness was manufactured. So you will need to confirm with your vendor whether your MS3X harness has a shielded CAM input or wait until you receive your parts and check it yourself. As far as I know, all DIYAutoTune MS3X harnesses now include shielded CAM/VR wires. If the harness you have doesn't, then you will need the shielded pair cable listed in the parts list and will need to modify your MS3X harness. Just to be clear, all MS3-Pro harnesses include shielded cables on the two VR inputs. No modification is required for MS3-Pro.

Stock Replacement Connectors

If you need to replace your stock CAS, TPS or coil connectors, LMS-EFI carries them.