Switching Carburetors To Fuel Injection: A Comprehensive Guide

how to change a carburetor to fuel injection

Carburettors are still used in racing and classic vehicle restorations, but many vintage vehicle owners are now converting to fuel injection. This is because fuel injection can improve fuel efficiency and performance in older carbureted engines. There are two basic types of fuel injection: throttle body injection (TBI) and multi-port fuel injection (MPFI). TBI is easier to install and cheaper, but MPFI offers better fuel distribution and engine performance. The conversion process involves removing the carburettor and installing injectors, a throttle body, sensors, and electronics. It requires some know-how and specialised tools, and there are fuel injection conversion kits available that make the process easier.

Characteristics Values
Reasons to convert carburetor to fuel injection Gas savings, fuel efficiency, improved performance, easier starting, better reliability, improved drivability in all types of weather and elevations, potential improvements in emissions and fuel economy, better fuel distribution, more horsepower and torque, cleaner tailpipe emissions
Types of fuel injection Throttle body injection (TBI), multi-port fuel injection (MPFI)
Considerations when choosing a type of fuel injection TBI is easier and less expensive but lacks some of the capabilities of MPFI; MPFI offers better fuel distribution and a better-running engine
Tools and equipment required for conversion Machining tools, wrench, welding equipment, injector manifolds, throttle body, sensors (oxygen, manifold air pressure, air temperature, coolant, throttle position), electronics, wiring, grommets, fuel pump, fuel lines, fuel hose and clamps, wire stripper/crimpers, drill and bit, fuel pump block-off plate, etc.
Steps involved in conversion process Remove carburetor, install injectors in intake manifold, install throttle body, install sensors, adjust distributor, set up electronics, connect vacuum lines, install coolant temperature sensor, connect fuel lines, remove and block off stock mechanical fuel pump, mount and wire power module, perform initial configuration, adjust throttle blades, start engine and check for leaks

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Removing the carburetor

Removing the carburettor is the first step in converting from a carburettor to electronic fuel injection (EFI). This process is critical for improving fuel efficiency and performance in older vehicles. Here is a detailed, step-by-step guide on how to remove the carburettor:

Remove the Air-Cleaner Housing: Start by taking off the air-cleaner housing and setting it aside. This will give you better access to the carburettor and the surrounding components.

Label and Remove Vacuum Lines and Wires: Before disconnecting anything, it is important to label all the vacuum lines and wires connected to the carburettor. This will make it easier to reconnect them correctly later on. Once labelled, carefully remove these lines and wires.

Disconnect the Throttle Linkage: Disconnect the throttle linkage from the carburettor. If your vehicle is equipped with a kickdown linkage, disconnect and set it aside as well.

Disconnect and Stopper the Fuel Supply: Disconnect the fuel lines coming into the carburettor. It is important to stopper the fuel lines to prevent leakage during the removal process.

Remove the Nuts Securing the Carburettor: Typically, there are four nuts securing the carburettor to the intake manifold. Use a suitable wrench to remove these nuts. If the carburettor is in good condition, you can consider selling it as a used part; otherwise, it can be discarded or recycled.

Lift and Drain the Carburettor: Carefully lift the carburettor off the intake manifold. Place it in a suitable container to catch any remaining fuel. Keep any linkage brackets in their original locations to ensure proper alignment during reassembly.

Clean the Intake-Mating Surface: Before installing the new EFI unit, it is crucial to clean the mating surface of the intake manifold. This ensures a proper seal and prevents leaks when the new unit is installed.

Install a New Gasket: Install a new carburettor-flange gasket on the intake manifold. This will provide a fresh seal for the new EFI unit. If the carburettor studs are not long enough, replace them with longer ones to secure the new unit properly.

By following these steps, you will have successfully removed the carburettor. It is important to note that this process may vary slightly depending on the specific make and model of your vehicle. Always refer to a qualified mechanic or a vehicle-specific repair guide for more detailed instructions.

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Installing injectors in the intake manifold

Step 1: Understand the Basics

Before beginning the installation, it's important to know the difference between throttle body injection (TBI) and multi-port fuel injection (MPFI). TBI serves as a carburetor replacement, and you can use your existing intake manifold. MPFI, on the other hand, requires changing the intake manifold and adding injectors and fuel rails. MPFI provides better fuel distribution and engine performance but is more complex and costly.

Step 2: Prepare the Intake Manifold

Most intakes can be modified by welding in bungs for the injectors. This step may require taking your vehicle to a machine shop for professional welding. Once the welding is done, the injectors can be slid into place, using O-rings to create a seal.

Step 3: Install Injection Fuel Rails

Injection fuel rails are necessary for the injectors to function properly. These rails will need to be machined to fit your specific engine. Depending on the conversion kit you choose, it may come with a ready-to-go manifold that accepts injectors.

Step 4: Connect the Fuel Lines

Ensure that your fuel lines are properly connected to the injection fuel rails. EFI systems typically operate at higher pressures than carbureted systems, so confirm that your fuel lines can handle the increased pressure.

Step 5: Optional Return Line

Most EFI systems require a return line from the engine back to the fuel tank. However, some EFI systems, such as those offered by Holley, are returnless and do not require this additional line.

Step 6: Test and Adjust

Once the injectors are installed, you will need to test and adjust the system. This may involve fine-tuning the exhaust system to ensure there are no leaks, as leaks can affect the accuracy of the oxygen sensors and the overall performance of the EFI system.

Converting a carburetor to an EFI system by installing injectors in the intake manifold can be a complex process. It is important to have the necessary tools, knowledge, and expertise to complete the installation safely and effectively. If you are unsure about any part of the process, it is always best to consult a professional mechanic or a certified EFI dealer.

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Installing the throttle body

The throttle body regulates the air going into the valves. Universal models are the easiest for conversions.

To install the throttle body, first, bolt the throttle body on and hook it up at the throttle linkage. This is connected to the accelerator pedal. An idle air controller is needed with the EFI throttle body. This goes into a small passage that pushes extra air past the throttle plates. It opens or closes the passage depending on how much air is needed in the manifold.

Most throttle bodies come with an IAC already installed. The throttle body portion of the assembly contains the throttle plates, idle air control valve, and throttle position sensor. The fuel body houses the fuel pressure regulator and one or two fuel injectors.

The vehicle’s fuel pump moves fuel from the gas tank to the throttle body assembly. Then a computer, often referred to as the powertrain control module (PCM), activates the TBI injectors. The injectors spray fuel into the throttle body bore and above the throttle plates. To control fuel pressure, the fuel pressure regulator routes excess fuel back to the fuel tank.

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Installing the sensors

Oxygen Sensor:

Install an oxygen sensor to monitor the amount of oxygen in the vehicle's exhaust. This sensor will help determine whether the ideal ratio of air to fuel is being achieved during the combustion process. It does this by measuring the oxygen levels in the exhaust, indicating a "rich" or "lean" mixture. A rich mixture means there is leftover fuel, while a lean mixture indicates too much air, both of which can lead to increased pollutant levels.

Manifold Air Pressure Sensor:

Mount the manifold air pressure sensor (MAP sensor) near or within the vehicle's intake manifold. This sensor measures the power load on the engine and compares it against a vacuum reading. It helps identify high engine load and higher fuel demands, such as when ascending a hill, and sends this data to the ECU to adjust the fuel injection accordingly.

Air Temperature Sensor:

Install an air temperature sensor, also known as a mass airflow sensor (MAF sensor), to measure the amount of air entering the engine. Air density changes with variations in altitude and temperature, so continuous measurements are necessary to maintain the correct fuel-to-air ratio. MAF sensors can be either hot-wire sensors or vane meters, with hot-wire sensors being the newer and preferred option due to their smaller size, responsiveness, and cost-effectiveness.

Coolant Sensor:

Place the coolant sensor, also known as the engine coolant temperature (ECT) sensor, beside the vehicle's thermostat. This sensor helps determine the impact of ambient temperature on the engine. When the engine is cold, the ECT sensor, along with the ECU, will make adjustments, such as increasing the fuel quantity and raising the idle for smoother ignition. Conversely, for warmer engines, they will invoke cooling fans or adjust the ignition timing to maintain optimal performance.

Throttle Position Sensor:

Install a throttle position sensor to provide direct feedback to the EFI system by measuring the position of the throttle valve. This sensor regularly monitors how far open or closed the throttle is and how quickly these changes are made. It provides data on how the vehicle is being driven and the power demands on the engine, ensuring smooth idling and on-demand acceleration.

These sensors are generally easy to install, as most of them screw into the engine. Ensure you have all the necessary components in your conversion kit. If any sensors are missing, you can purchase sensor packages separately.

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Adjusting the distributor

The type of fuel injection system you choose will determine the specific requirements for the distributor. A bank-to-bank EFI system typically works well with most distributors. On the other hand, if you opt for a sequential fuel injection system, you may need to use a dual sync distributor.

It is worth noting that converting to an EFI system offers significant advantages. One of the main benefits is improved fuel efficiency due to the system's ability to precisely control the air-to-fuel ratio, resulting in reduced fuel consumption and lower emissions. Additionally, EFI systems enhance engine reliability by maintaining an optimal air-to-fuel ratio, eliminating random engine stoppages and oiled spark plugs. The conversion to EFI also improves engine starting, regardless of weather conditions, by calculating the ideal air-fuel mixture for the given circumstances.

Frequently asked questions

Fuel injection can improve the fuel efficiency and performance of older carbureted engines. It also offers the ease of use and the ability to make changes while driving.

There are two basic types of fuel injection: multi-port fuel injection and throttle body injection. Multi-port fuel injection is the most common type and has a single injector for each cylinder. Throttle body injection is easier to install and requires less time.

You will need some know-how and a range of tools and equipment, including jack stands, a flare nut wrench, a penetrating lubricant, wire strippers/crimpers, a drill and bit, a fuel pump block-off plate, fuel hose and clamps, and 12-gauge wire with connectors.

The process involves removing the carburetor, installing the new fuel injection unit, connecting the vacuum lines, installing sensors, adjusting the distributor, and setting up the electronics.

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