Switching Carbureted Engines To Fuel Injection: Is It Possible?

The debate between carbureted and fuel-injected engines has been a long-standing one among car enthusiasts. Carbureted engines have a certain old-school charm, but fuel injection offers advantages that carbureted engines simply cannot match. One of the primary benefits of fuel injection is its ability to deliver the precise amount of fuel required for the air ingested by the engine, resulting in better fuel efficiency, increased horsepower and torque, and reduced emissions. This precision is made possible by the electronic control system in fuel injection, which constantly tweaks the air-fuel mixture based on the engine's needs. While converting a carbureted engine to fuel injection can be a complex and costly process, it may be a worthwhile investment for those seeking improved performance, easier starting, and reduced environmental impact.

Fuel injectors: Choose the right type and size for your engine

Converting a carbureted engine to a fuel injection system is a complex process that requires careful consideration of various factors. Choosing the right type and size of fuel injectors is crucial for optimal engine performance. Here are some detailed guidelines to help you make the right choice:

Horsepower Goals:

Firstly, determine your horsepower goals. The injector size you need is closely linked to the amount of horsepower you expect to achieve with your engine modifications. As a general rule of thumb, for gasoline, you'll need 1cc/min flow for each horsepower. So, for instance, if your goal is to achieve 1000 crank horsepower on 93 octane gasoline, you'll require a 1000cc injector.

Fuel Type:

The type of fuel you plan to use is another critical factor in selecting fuel injectors. Different fuels have distinct requirements; for example, ethanol-based fuels like E85 require approximately 30% more fuel to generate the same power as gasoline.

Injector Harness Plug Style:

The injector harness plug style is an important consideration. Common types include USCAR (ev6), Jetronic (ev1), Denso (Sumitomo), and Multec (Mini-Delphi). Ensure the injector plug style is compatible with your vehicle's fuel system.

Intake and Fuel Rails:

Consider which intake and fuel rails you will be using. This decision is crucial as it affects the compatibility and performance of the fuel injectors.

Impedance:

Determine whether you need high or low impedance injectors. This choice depends on the compatibility of your ECU (Electronic Control Unit). Most modern ECUs support both high and low impedance. You can use an ohm meter to test the impedance of your injectors.

Fuel Injector Flow Rate:

The fuel injector flow rate is a critical factor in sizing your injectors accurately. The industry standard flow rate is 43 psi/3 bar. The flow rate is typically conveyed in cc's per minute (cc/min) or pounds per hour (lb/hr).

Fuel Injector Dimensions:

Modern fuel injectors typically fall into three main sizes: 34mm, 48mm, and 60mm. The right dimensions will depend on the specific requirements of your engine and vehicle.

Fuel Injector Plug Types:

Fuel injectors come in various plug types, but the most prominent styles are Ev1/Jetronic (older models) and Ev6/USCAR (modern and more water-resistant). Ensure the plug type is compatible with your vehicle's fuel system.

Fuel Pump and Fuel Pressure:

Fuel injection systems operate at higher pressures than carbureted systems, typically between 43 and 60 psi. You may need to install a new, high-pressure fuel pump and a fuel pressure regulator to ensure optimal fuel delivery.

Remember, while bigger fuel injectors might seem appealing, they may cause flooding and damage to your engine if it is not set up to handle the extra fuel. Always consult a reputable car tuner or specialist to ensure you choose the right fuel injectors for your specific engine and performance goals.

Fuel pump and pressure: Install a new, high-pressure fuel pump and regulator

Fuel Pump and Pressure

Install a New, High-Pressure Fuel Pump and Regulator

When converting a carbureted engine to fuel injection, you will need to install a new, high-pressure fuel pump and regulator. This is because fuel injection systems operate at higher pressures than carbureted systems. Typically, carbureted systems operate at around 5-7 psi, while EFI systems operate at 43-60 psi.

There are a few different types of fuel pressure regulators to choose from, including deadhead (or blocking) regulators and return style regulators. Deadhead regulators are simpler and less expensive, as they do not require return plumbing. They are normally open, meaning fuel will flow through the regulator and be restricted once the pressure reaches its pre-set limit. However, this places an additional load on the fuel pump and can reduce its lifespan. Return style regulators, on the other hand, are normally closed until the pressure limit is reached, then they open the bypass outlet to return excess volume back to the tank. This reduces the load on the pump and can increase its lifespan.

When choosing a fuel pressure regulator, it is important to match it to the type of fuel delivery system and fuel pump you are using. Most lever-style mechanical fuel pumps do not require a regulator, and some electric fuel pumps have one built-in. If your fuel pump requires an external regulator, you will need to choose one that is compatible with your fuel pump and fuel delivery system.

In addition to choosing the right type of regulator, you will also need to consider the pressure requirements of your fuel injection system. Most fuel pressure regulators operate as either low-pressure devices (3-16 psi) or high-pressure regulators (40-70 psi). For a fuel injection system, you will need a regulator that can handle the higher pressure range.

It is also important to consider the location of the regulator. Deadhead regulators must be mounted between the pump and the carburetor, while return style regulators have more flexibility and can be placed upstream or downstream of the carburetor or fuel injectors. However, for optimal regulator performance, it is generally recommended to place the regulator near the engine so that it can quickly react to pressure changes.

Intake manifold: Replace or modify to accommodate fuel injectors

The intake manifold may need to be replaced to accommodate the fuel injectors. The specific approach will depend on the engine and fuel injection system design. In some cases, the existing manifold can be modified to accept the injectors.

The intake manifold is used to distribute the air and fuel mixture in throttle body injection (TBI) systems. In contrast, multi-port fuel injection (MPFI) systems use the manifold only to distribute air, with fuel injected directly above the intake valve of each port.

When replacing the intake manifold, it is not necessary to replace all the fuel injectors at the same time. If the injectors are in good working order, they can be retained, although it is advisable to check and clean them during the replacement process.

However, replacing all injectors simultaneously can have certain benefits. It ensures a coordinated and effective system, avoiding potential cascading effects from problems with individual injectors. It also maintains consistency and precision in fuel delivery, optimising engine efficiency and combustion.

If you are considering modifying or replacing the intake manifold, it is important to consult the manufacturer's specifications or service manual for precise information regarding the fuel injector location and any necessary modifications.

Fuel Injector Location

The location of fuel injectors in relation to the intake manifold can vary. In some engines, the injectors are positioned directly in the intake manifold, while in others, they may be located in the cylinder head or even in the combustion chamber.

Over time, the fuel injector's location has evolved, moving from the intake manifold to the combustion chamber. This change has improved the precision of fuel dispensing.

Signs of a Faulty Fuel Injector

There are several signs that can indicate the need to replace or service a fuel injector:

• Restrictions, electrical problems, or fuel issues causing driveability issues.
• A restriction of 8% to 10% in a single injector can cause a misfire and an overly rich fuel condition in other cylinders.
• Dirty injectors in turbocharged engines can lead to engine-damaging detonation.
• Injector nozzles may become clogged with fuel residue and waxy olefins due to heat soak when the engine is shut off.
• Increased or decreased fuel trims in the long-term or short-term.
• Insufficient resistance in the injector solenoid, leading to potential problems or failure.
• Longer crank times due to an injector leak causing a loss of pressure in the rail.
• Failed balance tests, indicating a clogged or malfunctioning injector.
• Significant pressure drop or no pressure drop when measuring the pressure loss in the fuel rail when each injector is fired.
• Lean misfire triggering a misfire code and turning on the check engine light.
• Vehicle failing to start with a full tank of fuel, which may be a symptom of contaminated fuel.
• Lack of maintenance, such as neglecting oil changes and filter replacements, leading to build-up on the injector tip.

Electronic Control Unit (ECU): Manage fuel delivery and ignition timing

The Electronic Control Unit (ECU) is a pivotal component of modern automobiles, acting as the brain of the vehicle. It is responsible for managing various functions, including engine performance, fuel injection, ignition timing, emissions, transmission, and other critical systems. The ECU collects data from strategically placed sensors throughout the vehicle and interprets it to optimise performance, fuel efficiency, and pollution production.

In the context of fuel delivery and ignition timing, the ECU plays a crucial role in ensuring the precise and efficient operation of the engine. It controls the injection of fuel and the timing of the spark to ignite it, using digitally stored equations and numeric tables. The ECU determines the position of the engine's internals using a Crankshaft Position Sensor, ensuring that the injectors and ignition system are activated at the correct time. This precise control of fuel injection and ignition timing results in improved fuel efficiency, increased power, and reduced emissions.

The ECU makes continuous adjustments to the engine's fuel delivery circuits and ignition timing, providing the proper air-fuel mixture and ensuring optimal combustion in the combustion chamber. This helps maintain the vehicle's peak power and economy levels. Additionally, the ECU can adjust fuel delivery and ignition timing based on various factors such as engine demand, temperature, and atmospheric pressure. For example, during acceleration, the ECU can adjust the throttle angle to complement the airflow through the engine, improving torque and drivability.

The ECU's role in fuel delivery and ignition timing is further enhanced by its ability to monitor and diagnose issues within the vehicle's systems. It can detect problems and generate error codes, aiding technicians in pinpointing and rectifying issues promptly. This diagnostic capability ensures that the vehicle maintains its optimal performance, fuel efficiency, and emission levels.

Overall, the ECU plays a critical role in managing fuel delivery and ignition timing, providing precise control, making necessary adjustments, and optimising the vehicle's performance, efficiency, and emissions.

Wiring harness: Connect the ECU to the fuel injectors and sensors

A fuel injection system is a complex upgrade from a carbureted engine, and the process requires a good deal of mechanical and electrical skill. It is not a simple task, and it is recommended that a trained mechanic is sought for assistance.

The wiring harness is a critical component of the conversion, connecting the ECU to the fuel injectors, sensors, and other electronic components. The ECU requires a dedicated wiring harness designed for a fuel injection system.

The ECU controls the air-to-fuel ratio of the combustion charge entering the engine by regulating the length of time the fuel injectors are open during each engine cycle. The ECU provides a ground connection, allowing current to flow from the power supply system, through the injector, and to the ground. The amount of current is limited by the injector's impedance.

There are two main groups of fuel injectors: high impedance and low impedance. High impedance injectors are the most common and simplest to wire and configure. They have two terminals: one supplied with 12 volts from the power supply when the engine is enabled, and the other wired to a dedicated injector output channel of the ECU. The ECU provides a ground connection to open the injector, and the simple switching strategy is known as saturated drive.

Low impedance injectors are wired in the same way but are controlled by the ECU in a more complicated manner. The ECU initially allows a large current to pass to open the injector quickly, and then limits the current to a lower level for the rest of the injection period.

The type of injector can be determined by measuring the resistance across the terminals with a multimeter. A high impedance injector will typically show a reading of around 12 ohms, while a low impedance injector will show a reading of 2.5 to 3 ohms.

It is important to ensure that the wiring harness is adequately cleaned and maintained to prevent problems. A fuel system cleaner can improve performance and clear any blockages.

Frequently asked questions