Sylvie Willis
Throttle Body Injection (TBI) is a type of fuel injection system that has one or two fuel injectors mounted in a throttle body. TBI systems were used in a variety of different production vehicles in the late 1980s and early 1990s, including the V6 and V8 engines found in General Motors (GM) pickups. While TBI might not be the most efficient fuel injection system, it is still an upgrade from a carburetor. TBI fuel systems use a spray bar positioned in the intake air-stream to draw fuel out as required. Fuel pump pressure on the inlet side of the regulator is blocked by a flow valve. This valve can only allow fuel to flow when the diaphragm experiences a drop in atmospheric pressure at the spray bar. The degree to which the valve opens depends on how much air passes the spray bar.
| Characteristics | Values |
|---|---|
| Type of fuel injection system | Throttle Body Injection (TBI) |
| Number of fuel injectors | 1 or 2 |
| Injector location | Mounted in a throttle body |
| Fuel delivery | Controlled by a "on demand" fuel pressure regulator |
| Fuel flow | Increased with an adjustable fuel pressure regulator |
| Fuel pump reliability | Reliable |
| Fuel economy | Decent |
| Fuel pump cost | Cheap |
| Fuel pump maintenance | Low cost |
| Fuel pressure | 10-13 psi |
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What You'll Learn
TBI fuel injection systems are found in older vehicles
Throttle Body Injection (TBI) is a type of fuel injection system that was commonly used in older vehicles, particularly those from the late 1980s to the early 1990s. It was phased out of production cars by the mid-1990s but is still found in many vehicles on the road today. TBI was a transitional technology between carburetors and more modern fuel injection systems like multiport fuel injection (MPI) and gasoline direct injection (GDI).
TBI fuel injection systems typically have one or two fuel injectors mounted in the throttle body. These injectors spray fuel into the throttle body bore or the air above the throttle plates. The fuel-air mixture then enters the intake manifold and is distributed to the engine's individual cylinders. TBI systems are often controlled by a computer, known as the powertrain control module (PCM) or engine control unit (ECU), which activates the injectors and adjusts the fuel-air ratio.
One advantage of TBI systems is that they offer good fuel economy, similar to that of a carburetor. They are also simple and easy to work on, with cheap and readily available service parts. TBI conversion kits are available for older carburetor-equipped cars, allowing owners to upgrade their vehicles' fuel systems and improve driveability and fuel economy.
However, TBI systems have some limitations. They are generally less efficient than newer fuel injection systems like MPI and GDI, which have an individual fuel injector for each cylinder. TBI systems also have lower power output capabilities compared to newer systems, as there is a limit to how much fuel can be pushed through the injectors. Additionally, TBI systems typically operate at lower fuel pressures than GDI systems, which can affect performance.
Despite these limitations, TBI fuel injection systems remain popular among vintage car enthusiasts and those seeking to upgrade their older vehicles' fuel systems. They offer a balance between the simplicity of carburetors and the improved performance and efficiency of modern fuel injection technologies.
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TBI is an electronic carburetor
Throttle Body Injection (TBI) is an electronic fuel injection system that serves as an upgrade from carburetors. TBI is a step up from carburetors and is found on older vehicles. It is a type of fuel injection system that has one or two fuel injectors mounted in a throttle body. The injectors deliver fuel into the air above the throttle plates, from where the air-fuel mixture enters the intake manifold and is distributed to the engine's individual cylinders.
Upgrading a carburetor to a TBI system can be done with a fuel injection conversion kit, which typically uses TBI. The conversion process involves swapping intake manifolds and distributors, installing sensors, mounting the fuel pump and fuel lines, routing and connecting the wiring harness and computer, and turning the key.
TBI systems were used in a variety of production vehicles during the late 1980s and early 1990s, particularly in General Motors (GM) pickups with V6 and V8 engines. While TBI might not be the most efficient fuel injection system, it is still an improvement over carburetors. TBI systems are also more economical and smarter choices for daily drivers, offering improved performance and fuel efficiency.
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TBI fuel systems are compact and simple
Throttle Body Injection (TBI) is a type of fuel injection system that has one or two fuel injectors mounted in a throttle body. TBI systems are compact and simple, and they served as a segue between carburation and multiport fuel injection (MPI). TBI is an electronic carburetor that performs the same function as a carburetor but uses electronic components instead of mechanical principles to get the air/fuel ratio correct.
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, directly above the throttle plates. The fuel pressure regulator controls fuel delivery and pressure, routing excess fuel back to the fuel tank to control fuel pressure.
The Rotec TBI Fuel System, for example, uses a spray bar positioned in the intake air stream. The venturi effect is utilized to draw fuel out of the spray bar as required. The TBI can run a wide range of fuel pressures, from 0.5 to 6.0 psi, and can even be gravity-fed. Starting the engine from cold is simple, requiring only the press of a diaphragm override button on the TBI regulator while cranking to give the engine a squirt of fuel to start.
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TBI fuel injectors are mounted in the throttle body
Throttle Body Injection (TBI) is a type of fuel injection system that has one or two fuel injectors mounted in a throttle body. TBI systems were used in a variety of different production vehicles during the late 1980s and early 1990s, including the V6 and V8 engines found in General Motors (GM) pickups.
TBI fuel injectors are indeed mounted in the throttle body, just below the throttle body and above the throttle plates. As the throttle body opens to allow air to flow into the engine, the TBI injectors spray fuel into the throttle body bore, creating an air-fuel mixture. This mixture then enters the intake manifold, where it is distributed to the engine's individual cylinders.
The TBI system is considered a transitional technology between carburetors and multiport fuel injection (MPI). It functions similarly to a carburetor but uses electronic injectors to pulse fuel over the butterfly valve of the throttle body. The main drawback of the TBI system is that it is limited in the amount of fuel that can be flowed through its one or two injectors, resulting in lower power output compared to more modern fuel injection systems.
Despite its limitations, the TBI system has its advantages. It is a simple and easy-to-work-on system with cheap service parts. Additionally, it offers good fuel economy and comparable power to carburetor systems. For those looking to upgrade their vintage car's carburetor, TBI conversion kits are readily available and can be a great option to improve performance.
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TBI fuel pressure can be increased for more power
Throttle Body Injection (TBI) is a type of fuel injection system that has one or two fuel injectors mounted in a throttle body. It is often found in vehicles from the late '80s and early '90s, such as General Motors (GM) pickups with V6 and V8 engines. TBI injectors are designed to run at between 11 and 13 psi, but it is common to see pressures around 10 psi.
Increasing fuel pressure is one way to enhance power in a TBI engine. A 1-psi change in fuel pressure can result in approximately a 4% increase in fuel flow, which can translate to an additional 8 to 10 hp. Adjustable fuel pressure regulators are available from companies like JET, Turbo City, and CFM Technologies, typically priced around $90.
Before installing an adjustable regulator, it is important to measure the existing fuel pressure. If the pump is already delivering 13 psi, an adjustable regulator may not be necessary. However, if the pressure is lower, an adjustable regulator can be used to increase it to the desired level, up to 13 psi.
It is worth noting that raising fuel pressure increases fuel delivery across the entire engine operating range. At part throttle, the oxygen sensor should detect a rich mixture and adjust the mixture back to the ideal 14.7:1 air/fuel ratio. At wide-open throttle, the computer switches to its base fuel map, and the additional fuel pressure will increase fuel flow, resulting in increased power if the engine requires the additional fuel.
Another method to enhance power in a TBI engine is to use swirl-inducing TBI spacer plates, available from CFM Technologies, Trans-Dapt, AirAid, JET, and other manufacturers, typically priced between $50 and $100. Additionally, installing a longer-duration camshaft with more lift will significantly improve airflow and power at higher engine speeds, but it will require changes to the base fuel map in the computer.
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Frequently asked questions
Yes, TBI motors have a fuel filter.
TBI, or throttle body injection, is a type of fuel injection system that has one or two fuel injectors mounted in a throttle body.
The vehicle's fuel pump moves fuel from the gas tank to the throttle body assembly. A computer, often referred to as the powertrain control module (PCM), then activates the TBI injectors, which spray fuel into the throttle body bore above the throttle plates.
TBI motors are known for their reliability and fuel pump reliability. They are also simpler to work on than newer high-pressure fuel systems and are generally cheaper to maintain.
