Dr. Scott M. Baker

Fuel Injection Components

When you’re designing a custom fuel injection system, you need a lot of parts. Most of these parts will be either aftermarket parts (i.e. MSD) or parts from existing fuel-injected vehicles. As far as sourcing used parts, ebay is an excellent source. I generally liked dealing with ebay better than dealing with the local junkyard.

Throttle Body

    A throttle body is like a carburetor but without all of the ‘fuel stuff’. In fact, some people will take carburetors and disable the fuel circuits, vents, etc and use them as throttle bodies. Generally you want a throttle body that has a Throttle Position Sensor (TPS). The TPS tells the computer how far open the throttle is and is used for acceleration enrichment, flood-clear mode, etc.The throttle body I used was off a late 1980’s ford escort. The TPS is built in, and the IAC solenoid (more on that later) is attached to it. I was able to get the whole thing (including TPS and IAC) for $10 plus shipping from Ebay.

    The one thing you usually don’t get are the connectors for the TPS and/or IAC. Expect to pay about $20 bucks for those. Yes, that’s right the connectors cost more that than throttle body did.

IAC Solenoid or Motor

    IAC stands for “idle air control” and controls how much air goes into the motor during idle. There are several different versions of this, including simple on/off valves (used to select between a fast idle and a slow idle), motors that can precisely control idle, and PWM idle valves.The Ford throttle body that I used came with a PWM idle valve. This thing starts fully open, and closes in proportion to the amount of voltage (that’s not entirely correct, but close enough) that you give it. When you start your motor, the computer senses that the engine is cold and leaves the valve open a bit. As the engine warms up, it closes the valve a bit.

    I never did get the ford IAC to work quite right. The megasquirt is supposed to be able to open it in varrying amounts, but I found that it tended toward a fully-open or fully-closed state. I suspect the ford computer probably uses PWM with active feedback to achieve a desired state whereas the megasquirt just sets a PWM value and assumes that will hold the solenoid open a specific amount.

IAT Sensor:

    The computer needs to know the temperature of the incoming air. I used a GM “open cell” sensor from DiyAutoTune. The open sensor is important for Turbo vehicles as it allows the computer to sense temperature changes more rapidly.

Coolant Sensor

    Yes, that’s right, we need a coolant sensor. Problem is, we have no coolant. Well, that’s actually not true — we do have coolant and it’s called ‘air’. I used a GM-style coolant sensor from DIYAutoTune and mounted it to the lower cooling tin on the #2 cylinder. A friend gave me the helpful advice of building a mount for the sensor using a big washer and then attaching the washer to the tin — thus avoiding having to remove the tin (which would require removing the pushrods) in order to do the fabrication.

Crank / Distributor / RPM Sensor:

    The computer needs to know how fast the motor is turning. There are multiple ways to do this, the easiest is to use your distributor and pick it up from the points. Using an electronic module like a compufire or pertronix is highly recommended as it cleans up the signal compared to the noisy mechanical points. I had an MSD box left over from the Mazda build, so I used the MSD box’s tach output to get things started.Note: The ‘right’ way to do it is to lock out the timing on your distributor, and let the computer do the advance, and let the computer control the ignition. However, if you just want to get things working, then you can postpone this part until later.

Injection Manifolds / Fuel Rails:

    I decided to go with port injection, and CB performance makes handy injection end casings. These look like regular end-casings and work exactly like them, except that there are injector bosses mounted in them.I also went with the CB performance fuel rails so that I could use their brackets and injector clips. Making your own rails is also an option and it will save you a fair bit of money. CB’s rails are $60 plus $6.95 for each clip. The clips are nice as they prevent the injectors from being able to pop off the rail if the rails ever came a bit loose from the motor.

Fuel Pump:

    For port injection, you want something capable of delivering a minimum of 45 psi. MSD makes a good aftermarket pump.

Fuel Regulator:

    I went with the MSD boost-sensing regulator, which is actually a rebranded bosch unit.

Fuel Gauge:

    I used a summit 60psi gauge mounted to the fuel rail.

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