ECU

I chose to install the Rotary Aviation EC3, and this guide is written for the latest version of that device at the time of this writing. The EC3 is relatively inexpensive, has dual, switchable computers for redundancy, and has a manual mixture knob - all helpful features for aviation use. As icing on the cake, Tracy Crook provides excellent support for builders and flies his own product, so he's constantly improving it.

Just to round out the picture, if you prefer an alternative I believe the best choice is probably the Megasquirt. This is a somewhat-DIY device that you can buy assembled or in kit form (if you're pinching pennies and are skilled with a soldering iron). It will take longer to install this device than the EC3, but if you're a techie it does have some interesting features (like the ability to respond to a knock sensor, support a second CAS, etc.) that make it worth a look. If you do decide to go that route, check out Aaron Cake's MegaSquirt RX-7 Guide. It's written for the 2nd-gen engine, but most of the rules apply to the 3rd-gen and the guide will give you a huge running start.

Assuming you've decided to use the EC3, start by installing three switches on your panel:

• 1x (ON)-OFF-(ON) DPDT momentary (B&C S700-2-7) coil disable¹⁾
• 1x ON-OFF-ON DPDT (B&C S700-2-1) primary injectors
• 1x ON-OFF-ON DPDT (B&C S700-2-1) secondary injectors

The wiring for these switches isn't complicated but there are a number of connections to make. I've included a closeup of Tracy's diagram here as well as a labeled photo of my own installation for your reference.

Fig. 1: Labeled Installation Photo

Fig. 2: Switches Wiring Diagram

This is optional, but I recommend bundling these wires together into a harness. You can buy pre-made harnesses or multi-conductor cable, or just use heat-shrink tubing. If you use heat-shrink tubing, do a flame-test first to make sure it is flame-retardant / self-extinguishing. Most products are designed for automotive use, but a few aren't, and they're not always well labeled. It's worth a quick check to be sure²⁾. Since there are only three wires involved here I just used a 3-conductor cable from B&C.

Route the 3-wire injector wiring bundle to and through the firewall with about 3' of extra length. Make up a second bundle of 5 wires to run from the EC3 with the same extra length. Cut these two bundles to reach an ideal termination location (I put mine on top of the block, under the intake). Then trim the heat shrink/insulation and crimp a Mate-n-Lok male pin onto each wire. Slide a 2” length of heat-shrink over both wire bundles, install the pins into a Mate-n-Lok plug per the diagram below, and finally shrink the tubing for a clean finish (and strain relief).

Follow the same procedure to build a Mate-n-Lok jack that connects to four fuel injector connectors with enough wire length to reach the injectors from the plug. Note that there is a jumper on this side of the connector between pins 7 and 8. This is the injector-disable switch that connects to the EC3, J1 pin 7. You could run this wire directly to the EC3, but it's the only wire in this bundle that would go that way, so I felt it was easier to just run it with the rest of the bundle.

Be careful to identify which pin is + on each injector³⁾. If you have the factory wiring harness you can just look at (or even re-use) the injector plugs. The + terminal is Black/Yellow on all four injectors. The - terminal is color coded separately for each injector. On my installation, the + terminal was the front pin, nearest the firewall. Note that because of clearance issues with my intake, I'm using a modified/trimmed injector connector installed semi-permanently with RTV. If you have room, you can use the stock (or sourced from eBay) injector plugs.

Fig. 3: Injector Wiring Diagram

Fig. 4: Quick-Disconnect for Injectors

Cut six 1-3/8” lengths and four 1” lengths of 1/4” hard aluminum tubing and sand to ensure all lengths match. Then cut two 9” lengths of 1/4” fine-pitch (to match a -4 nut) all-thread rod. Lay out the coil packs next to one another and assemble as shown in the pictures below, with the longer spacers between the coil packs and the shorter spacers on the ends.

Now measure the final length of the assembly plus spacers and bend a 1/8” x 2” x approx. 15” aluminum bar into a U-shape as shown to support the assembly. Mark and drill 1/4” holes on the ends to slide the all-thread rods through as well as holes in the back plate to mount to the firewall. Three holes (two top, about 6” apart, one bottom center) is more than sufficient to mount the assembly. Finish the assembly with 1/4” bolts, nuts and washers as required, and attach to the firewall near the top-left cowl line, low enough so the coil packs don't interfere with the cowl itself but high enough to leave room for other items below.

Fig. 5: Coils Assembly, loose

Fig. 6: Coils Assembly, installed

To wire the coil packs, it is best to use a wiring harness designed for the task (coils are very hard to solder directly onto - the pins are recessed). eBay is a good source for these connectors (search for “LS1 coil connector”). Wire the coils per the EC3 wiring diagram. Note that a capacitor is recommended here. I installed mine just below the coil packs using wire ties, but any suitable location close to the coil packs is fine.

Finally, fabricate a blast tube from your NACA plenum to cool the coil packs, making sure the tube doesn't interfere with the control rods and pulleys nearby.

Build a wire harness using 14x 22ga wires and a long length of heat-shrink tubing. I strongly recommend using color-coded wires here, because mis-wiring is the most common source of trouble with EC3 installations. Your length will vary depending on where you install the EC3; mine worked out to about 10', but your mileage may vary. Spend a few bucks and make it longer than you need to. You can always coil up the extra length and tuck it away next to the EC3 to give you maneuvering room if you ever decide to move it. Then run this harness between your panel and your desired EC3 installation location.

Next install the EC3 control panel in a suitable location in your panel. You'll need to drill four (#28 works well) holes for 6-32 mounting screws, plus cut a rectangular slot for the device itself. The top DB-15 connector sticks out a little bit. As you can see in the photo below, I cut a somewhat oversized slot for this to fit through. I'll micro it back in later before I paint my panel.

Fig. 5: EC3 Panel Installation

Fig. 6: EC3 Panel Wiring

Split out 3x wires from the harness and crimp a 1/4” FastOn connector onto each. These should connect to the Injector and Coil Disable switches as illustrated above. The remaining 11x wires terminate in a DB-15 solder cup connector supplied with the EC3. If you aren't sure how long to cut your wires, use heat shrink on the bundle itself as I've done in the photo above. After you solder all of the wires, you can slide the heat shrink up onto the bundle to provide a clean finish where the strain relief grips it.

It's beyond the scope of this document to teach you how to solder (refer to the Aeroelectric Connection if you need help), however here are a few tips for working with solder-cup style connectors that can help you achieve a neat finished product like the one shown in the photo:

1. Don't over-strip your wires. Solder cups aren't as deep as they look. Strip just enough to let the wire bottom out in the solder cup with only a small amount of wire showing (usually 1/8”.)
2. Mark the connector pin numbers on the connector with a Sharpie. They're very hard to see to begin with - once you get going, they're even harder to pick out.
3. Before you close up the connector, look for any cold solder joints. Each solder cup should be filled but not overflowing, solder should be visibly “wicked” into the strands of each wire, and the surface of the solder should also be shiny and smooth, not dull or “pebbly”.
4. Use a pencil-tip electronics soldering iron (25-35W max).
5. Clean the tip before EVERY connection. A quick swipe across a damp sponge or a quick, light scrape with a razor blade is all it takes. If the tip isn't shiny, it won't work!
6. Optional: if you fill a plastic syringe with a “no clean” (important!) water-based resin and dab a tiny drop into each solder cup before you solder it, the results will amaze you.

When you're done, attach the DB-15 connector to the EC3 control panel to complete the installation. If you'd like a little added insurance, there's room to safety-wire the connector as long as you're careful not to short anything out. But I recommend waiting until your engine is running well - just in case!

You should now have a spaghetti pile of wiring in your engine bay.

Before you can install the EC3 you may as well take care of some of the basic subsystems. The starter and alternator wiring are a key part of testing the engine, and you can get them out of the way before the EC3 even arrives.

Wiring is a very religious subject, and there are many ways to skin this cat. If you want my full wiring diagram, look at my main project site, particularly chapters 22 and 23. My setup is a little odd because I installed my batteries just behind the front seatback, with a manual battery switch. That means I have no contactors.

Regardless of how you get there, start by establishing a SOLID ground connection from your battery to your engine block. Ideally this would be a 4AWG wire from your battery terminals to one of the starter mounting bolts (since the starter is the biggest consumer while it's running, and benefits from having the lowest-resistance path possible) and from there to a ground block on the firewall.

B&C sells a “Ground Block 24/24-TAB Firewall Kit” which provides two 24-tab ground blocks with bolts that connect them together on both sides of your firewall. This is a very convenient way to provide ground connection points for your engine, ECU, and related components.

Next run a 4AWG B+ cable to the B+ connections on both the starter and alternator. Depending on your design you may or may not want to run these through ANL current limiters, ammeter shunts, and/or contactors. That decision is up to you, but here's what I did:

1. B+ from alternator to an ANL current limiter.
2. Current limiter to ammeter shunt.
3. Ammeter shunt to starter B+, also to battery +.

This setup gives me over-current protection for the alternator (that kind of thing starts fires) and the ability to monitor charging current. If alternator charging current falls to or below 0 (or some minimum “house load”) while the engine is running, you know your alternator has failed and you're running on battery. I have two batteries and on a minimum load I can run 45m to engine failure. Detecting alternator failure early gives me time to divert and land safely to diagnose the problem.

During the early phase of a flight this is also an indication of battery health. The battery should typically take some amount of time to recharge from the alternator after starting the engine. I plan to rotate my batteries yearly, but even so it's nice to be able to detect premature failure. A battery that's taking too long to recharge is an indication of this. Without any other changes in electrical load, the alternator current should slowly and steadily fall from its initial value, then level off once the battery is charged.

The starter will need a wire run from its S terminal (the 0.250” FastOn terminal on its side) to a starter button, and from there to B+. This should be fused for safety. I measured 6.3A draw on my starter so I went with a 10A fuse and a pushbutton capable of handling 10A @ 12VDC.

Once you get all this hooked up, run a test of the starting system. It's a good idea to rig up a switch in the engine bay temporarily, just a button or momentary switch that shorts B+ to S on the starter. When you're ready, turn on the power and hit the button for a few seconds. After the glee wears off, run it again a bit longer and watch for any play or runout in the moving components.

If you're planning on performing a compression test, do that now as well. Note that Mazda calls for this to be done at 250rpm, which requires fresh batteries to achieve.