Part 3 – EFI Sensors and Hardware There are a few different sensors and other EFI hardware that you need to install as part of an EFI swap. When using the MegaSquirt ECU, you can literally pick and choose what equipment you would like to use depending on what you want to achieve. Below is a list of the EFI components I chose to use, along with a little information on what each component does.

Throttle Body:
Using throttle body injection (TBI) is great for an EFI swap because it allows you to put a few different EFI components in a single package while allowing you to keep a lot of your existing engine components. Below is a picture of the installed holley TBI.

Below is a closer view of the throttle body with the major EFI components labeled.

Fuel Pressure Regulator: This is what controls the fuel pressure. Because with TBI the fuel injectors are located before the throttle plate, the fuel pressure regulator does not need to be vacuum referenced.

Throttle Plate: The throttle plate is what controls the amount of air entering the engine. The throttle plate is ultimately what controls the power output of the engine.

Fuel Injectors: These fuel injectors squirt right down into the throttle bores with a conical spray pattern. Even when only at 16PSI they fog the fuel quite nicely. With an open and close time of under 1.0ms these injectors will allow for precise control of the amount of fuel delivered to the engine.

Idle Air Control: This is basically an adjustable air leak. The IAC valve controls the amount of air entering the engine at idle. This IAC valve opens and closes in 255 very small steps allowing me to finely adjust the idle speed and very the idle speed for different engine temperatures or conditions (such as to speed up idle when AC is on).

Throttle Position Sensor: The throttle positions sensor (TPS) tells the Electronic Control Unit (ECU) how far open the throttle plates are. The ECU uses this information to invoke acceleration enrichment (like an accelerator pump on a carb), it’s also used to control “Flood Clear Mode” during engine cranking. The TPS sensor DOES NOT tell the ECU how much fuel to inject. The ECU relies on the manifold absolute pressure(vacuum) sensor and engine RPM to determine how much fuel to inject.

Coolant Temperature Sensor:
Below is a picture of the coolant temperature sensor. As you can see I put a “T” fitting in the line that goes to the heater core. This seems to work well but looks a little funny to me. I plan a manifold swap in the future and when I do, I will have a proper hole tapped in the manifold for this sensor. Until then I live with an engine that looks like it’s owned by a plumber. The coolant temperature sensor is used to tell the ECU (Electronic Control Unit) the temperature of your engine. The ECU uses this data for many things including air/fuel ratio adjustment, Idle speed adjustment, Cooling fan control, Cold start enrichment, etc.

Intake Air Temperature Sensor:
Below is a picture of the intake air temperature sensor (IAT) mounted to the lower air cleaner. The air cleaner assembly I bought had a spot to mount EGR hardware and I chose to mount the IAT sensor there although anywhere would have worked. The IAT sensor tells the ECU the temperature of the air entering the engine. The ECU uses this information to make small changes to the air/fuel ratio. Installing this particular sensor was as simple as drilling the hole, placing the sensor in the hole and then sliding in the retaining clip.

O2 Sensor and Controller:
Below is a picture of the installed O2 sensor as well as the controller. I took the car to a local exhaust shop to have the bung welded into my H pipe. From there it was a simple job of screwing in the sensor and strapping the controller to the transmission cross member. The O2 sensor sends Air/Fuel ratio information back to the ECU. The ECU then uses this data to make changes in the amount of fuel injected. A controller in only needed with wideband O2 sensors as wideband sensors are a lot more complex than a standard narrow band O2 sensor.

ECU (Engine Control Unit):
Below is a picture of the Megasquirt ECU sitting in it’s temporary home on the passenger side floor. Eventually it will be mounted to the firewall near where the passenger’s feet will be. The ECU is the “brains” of the EFI system and what my laptop will plug into in order to program and monitor the engine. In the bottom right hand corner of the ECU underneath the connector for the main harness you can see the vacuum line that connects to the ECU’s built in Manifold Absolute Pressure (MAP) sensor. The MAP sensor is basically an electronic vacuum sensor that tells the ECU what the manifold vacuum is. The ECU then uses this data to decide how much fuel to inject.

Engine Compartment:
Below is a picture of the engine compartment with all of the EFI equipment installed. As you can see, it’s difficult to tell at 1st glance that this is not a carbureted engine. You can see some additional wires but those will be properly hidden once the wiring is complete. The other give away is the coolant sensor, but once I remove the intake manifold and tap a proper hole for this sensor, you’ll hardly be able it see it either.