Custom MegaSquirt DIY EFI Conversion on a Ford 302 Windsor V8
Written By: BottleFed70

Megasquit DIY EFI Introduction
Part 1 – Parts and Equipment Used
Part 2 – Fuel System
Part 3 – EFI Sensors and Hardware
Part 4 – Assembling the MegaSquirt and Wiring
Part 5 – Tuning
Part 6 – Ignition Control and Tuning

Part 1 – Parts and Equipment Used
In this section of the document, I will outline all of the parts I chose to use for my fuel injection kit . I will only state the purchase price. I’ll leave it up to you to determine what your shipping fees, taxes, import fees, etc will be. All prices are in US dollars.

Kit Contents: Megasquirt II V3 PCB
Megasquirt Relay Board and Relay cable This is how the fuel injection kit came in the mail. This kit used version 3 of the Printed Circuit Board(PCB), and uses the Megasquirt II processor. There are various different revisions of the PCB and processor… this one is the latest and greatest, but is also the most expensive. I ordered this kit from for $250. I should make it clear that this is a 3rd party company that will gather the parts needed for you and then sell them as a kit. Or you can buy a completely assembled ECU from them. I’m very impressed with the quality of the kit and the service from the seller. Everything is clearly labeled and the kit is very complete. As you can tell, it’s not assembled…I plan on building it myself. I could have saved a few $$ by purchasing all of the components, case, etc myself. But the money saved wasn’t worth it to me for all of the extra work involved. Plus this kit came very well labeled, which greatly helps with assembly.

- MSI fuel injection kit with PCB2.2 $130 (less features)
- MSII kit with PCB3 pre-assembled $410 (less work)
- Ordering all components separately (PCB, case, electronics, etc) $220

Megasquirt Relay Board and Relay cable:
Megasquirt Relay Board and Relay cable Megasquirt Relay Board and Relay cable The relay board is designed to mount in the engine compartment. It holds the relays for your fuel pump, main power, and fast idle solenoid as well as fuses. It is also designed so that all wiring goes to the relay board. There is a cable that connects the relay board to the ECU which is usually put in the passenger compartment. The relay board is NOT NEEDED, you could wire everything directly to the ECU! However, it greatly simplifies wiring, and helps to keep everything looking professional. The relay board is especially helpful for installs where you are converting a non-EFI vehicle. Previously injected vehicles usually already have most of the wiring, relays, and fuses in place.

I chose to buy a pre made relay cable as these cables can be difficult to build and very time consuming. You could easily make your own. The relay board kit and cable were purchased from Relay kit was $65, cable was $70. I’m very happy with the quality of the product and service from the seller.

- No relay board and cable - wire directly to ECU. Cost would only be whatever you spend on relays, wire, and fuse holders. Cheapest would be to raid the junkyard so it would cost maybe $30?
- Assembled relay board - $90 (instead of $65 for kit)

MegaSquirt Stimulator:
MegaSquirt Stimulator The stimulator plugs into the ECU and mimics a running engine. This little gadget is used to test your ECU. It’s absolutely necessary to have one of these if you plan on assembling your ECU yourself. If you are planning on buying a pre assembled ECU then whomever built it should have tested it already so you probably don’t need one. However, they are pretty cheap so I’d suggest getting one anyways.

I bought a pre-assembled stimulator from for $75. And was very happy with the quality and service of the seller. This is the only component I bought pre-assembled. Because I plan on using it to test the ECU, I want to be absolutely sure it was working properly. Nothing sucks more than having a problem and not knowing if it’s the ECU or the Tester that you assembled wrong.

- Unassembled kit $40 (instead of $75 for pre-assembled)
- No stimulator $0

ECU to Laptop cable (tuning cable):
ECU to Laptop cable You’ll need to buy a serial (DB9) cable to connect your laptop to your megasquirt ECU. If your laptop is like mine and doesn’t have a serial (DB9) port, then you’ll have to purchase a USB to serial adapter.

The cable cost $7 and the adapter $22. They are available in any computer store.

Throttle Body Injection Unit:
Throttle Body Injection Unit In order to keep with the classic carbed appearance and to also limit costs without sacrificing horsepower, I decided to use throttle body injection (TBI). TBI has some advantages in that it includes a lot of components in a small package (Idle air control, Fuel injectors and fuel rail, Throttle position sensor, Fuel pressure regulator, etc) it’s also an easy install especially with a universal 4bbl TBI like this holley one. It also helps to keep costs down as it doesn’t require the purchase of a new intake manifold and allows me to keep my carb style nitrous plate.

TBI does have a bit of a downside however. Since the injectors are located farther away from the valves (unlike multiport), there is slightly less throttle response. But it’s still light-years better than a regular carb. Many people believe that TBI systems make less power. This is not true, and if anything it’s the exact opposite. Generally the farther away you keep the injectors from the intake valves, the more power you’ll make. This is because it gives the fuel more time to evaporate (better atomization) and because as the fuel evaporates it cools the air (colder intake air temps).

This TBI unit started out life as part of a Holley fuel injection kit conversion. I purchased it off of ebay for $340. When I took it apart, it appears as tho it’s never been used. What happened to the other components of the Holley kit, I don’t know. This TBI is rated at 900cfm and has 4 x 85pph injectors. It’s good up to approx 600hp. Too big for my engine, but that’s the beauty of a programmable ECU…you can make it run like it was designed for the engine. The long term plan is to strap on a supercharger, so I wanted to get something that would work for the SC as well.

- Junkyard factory EFI equipment from newer 351W truck engine $400
- New EFI performance intakes, injectors, rails, and throttle body $1200
- Junkyard 2bbl TBI from a late 80’s chev 350 and manifold adapter plate. $250

Fuel Pump:
Fuel Pump When converting to fuel injection, you’ll need to install a fuel pump and related components for a higher pressure fuel system. I chose to use a Warlbro inline external fuel pump rated at 255lph. This pump is larger than I need and will support up to approx 500hp. I bought the larger pump for future plans. This pump was bought off of ebay for $110 and includes everything needed for installation.

- Warlbro 190 lph (good to 350hp) new pump $65
- Used/Junkyard 190 lph pump $30

Fuel line and fittings:
Fuel lines There are a few different choices available to you in regards to fuel line. Just make sure it can handle the pressure of the fuel system you plan on using. I chose to use steel braided hose of a 3/8ths diameter. The 25’ roll pictured is made by spectre and cost $65 on ebay the hose clamps are also made by spectre and cost $10 for a 10-pak. This isn’t a real braided hose, but rather a regular rubber hose wrapped in a steel braid. It’s rated up to 55psi which should be plenty considering my TBI injectors are only meant to work at approx 20psi.

I chose to run this line because the price wasn’t bad, it’s flexible and easy to route, and because it looks good.

- Regular high-pressure black fuel line - $40 + fittings
- Solid stainless steel or aluminum lines - $40 + fittings
- Real aircraft quality braided lines - $200 + fittings.

Fuel filters:
Fuel filters You’ll want to run a fuel filter (or 2) in your fuel system. I chose to use 2 filters. A high volume low pressure (top) “pre filter” and a high pressure low volume (bottom) after filter. The larger filter is a generic summit brand and cost $10, the smaller filter is made by earls performance and cost $30. Both were ordered from summit racing. The key thing with fuel filters is to make sure they can handle the pressure and that they have the fittings you need.

- No pre filter (saves $10)
- Only pre filter (saves $30)

Fuel Pressure Gauge:
Fuel pressure gauge If you want to use an adjustable fuel pressure regulator, you’ll also want a fuel pressure gauge. This gauge is just a small cheap gauge that I got from summit for $20. I plan on mounting it under the hood near the fuel pressure regulator.

- No Gauge $0
- Fancy in-dash gauge with electric sending unit $150

Fuel Pump Blockoff Plate:
Fuel pump block off plate Since you’ll no longer be using your stock mechanical pump, you’ll want to remove it and install a fuel pump blockoff plate in it’s place. I bought this one from summit racing for $7. Looks like it’ll do the job wonderfully.

Wideband 02 sensor and controller:
Wideband Sensor and controller I chose to use a wideband O2 sensor. With the megasquirt ECU you can run either a regular O2 sensor or a wideband sensor. A regular O2 sensor is what comes in 99% of today’s vehicles and only tells the ECU “rich or lean”. A wideband sensor will tell the ECU exactly how rich or how lean the engine is running. This is especially useful when tuning for power or fuel economy. Unfortunately with a wideband sensor, you need an extra piece of hardware called a controller.

Pictured is an innovative motorsports LC1 kit with sensor. It cost $200 from and looks great. The LC1 kit comes with the sensor, exhaust bung, controller, and software to connect directly to your laptop. To run a wideband O2 sensor, you’ll need everything in this kit except for the software.

- Regular 02 sensor new $60
- Junkyard regular O2 sensor $20
- No O2 sensor (not recommended) $0

Coolant Temperature Sensor:
Coolant sensor You’ll need to install a coolant temperature sensor. Unfortunately, sharing your factory sensor with the gauge doesn’t usually work. The megasquirt ECU will work with any coolant temperature sensor, but it’s configured by default for the GM sensors. It’s usually easiest to use a GM sensor. I plucked this one from my local junkyard, it’s out of a 92 chev cavalier and it set me back $5. Alternatives: - You could use a new sensor instead of junkyard $20

Intake Air Temperature Sensor:
Intake air temp sensor You’ll also need to install an intake air temperature sensor. This sensor measures the temperature of the air coming into your engine. The pictured sensor was also taken from a local junkyard and cost me $5.

- You could use a new sensor instead of junkyard $30

Wire You’ll need wire to wire everything up. Preferably you’ll want various colors and thickness. I went to a local store and spent $40 to add some roles of wire to my collection.

- I suppose you could salvage wire from a junkyard $10
- You could buy only the wire you’ll need by the foot $25

Wire Connectors:
Wire connectors You’ll need a few wire connectors. Preferably something weatherproof and durable. I chose to buy a “weatherpack connector kit” from ebay for $65. This kit has everything I need and enough connectors to do 5 conversions. These connectors are the same ones that GM uses in their vehicles and are about the best you can get. Very professional looking and great to work with.

- You could cut connectors out of junkyard cars and re-solder them $10
- You could only buy the few connectors you need instead of a complete kit $25

Part 2 – Fuel System