Mercedes Mullins
The presence of a throttle body or fuel injectors in a car depends on the type of engine. Throttle body injection (TBI) is a type of fuel injection system where one or two fuel injectors are mounted in the throttle body. TBI was used in cars from the late 1980s to the early 1990s and has been largely replaced by multiport injection (MPI) and gasoline direct injection (GDI). In a fuel-injected engine, the throttle body controls airflow, while the injectors control fuel flow. Modern engines may have both MPI and GDI fuel injection systems, with one injector per cylinder.
Does my car have a throttle body or fuel injectors?
| Characteristics | Values |
|---|---|
| Throttle Body Injection (TBI) | A type of fuel injection system with one or two fuel injectors mounted in a throttle body. |
| Usage | TBI was phased out of production cars by the mid-90s, but many vehicles with TBI are still on the road. |
| Conversion | TBI conversion kits are available to update an engine's fuel system from a carburetor to fuel injection. |
| Function | The throttle body controls airflow, while the injectors control fuel flow. |
| Fuel Delivery | The vehicle's fuel pump moves fuel from the gas tank to the throttle body assembly. |
| Fuel Injection Types | Multiport Injection (MPI), Gasoline Direct Injection (GDI), and Direct Injection are other types of fuel injection systems. |
| Engine Requirements | An engine needs air, fuel, and spark to run. |
| Airflow Control | The throttle body regulates airflow to the intake valves. |
| Fuel Injection Location | In modern cars, fuel injectors are usually located in the heads, not the throttle body. |
| Intake Valve | The intake valve lets air/fuel into the cylinder. |
| Fuel Injection Timing | In direct injection, fuel is injected directly into the cylinder, not the intake tract. |
| Throttle Body Components | The throttle body assembly contains throttle plates, an idle air control valve, and a throttle position sensor. |
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What You'll Learn
- Throttle body injection (TBI) is a type of fuel injection system
- TBI was phased out in the mid-90s but some cars still use it
- The throttle body controls airflow, while injectors control fuel flow
- Direct injection engines inject fuel directly into the cylinder
- Conversion kits can update a carburetor to a TBI system
Throttle body injection (TBI) is a type of fuel injection system
TBI systems were used in a variety of different production vehicles during the late 1980s and early 1990s. Some of the most well-known applications are the V6 and V8 engines found in General Motors (GM) pickups. Although TBI was phased out of production cars by the mid-1990s, many vehicles that employ the technology are still on the road. TBI might not be the most efficient out of the three primary types of fuel injection systems (the other two being MPI and GDI), but it’s still better than a carburetor.
In modern port-injected cars, there is a throttle body that houses the throttle butterfly valve that lets in air and the injectors add the appropriate amount of fuel. This all happens outside of the cylinder. A direct injection car is pretty much the same except the fuel is injected directly into the cylinder.
In fuel-injected applications, the throttle body controls airflow, while the injectors control fuel flow. The throttle body regulates air and the fuel is controlled elsewhere. All engines use a throttle body to regulate airflow; otherwise, you would constantly have essentially 100% throttle and just keep revving.
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TBI was phased out in the mid-90s but some cars still use it
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 found on older vehicles, usually those from the late 1980s and early 1990s. TBI was a segue between carburation and multiport fuel injection (MPI).
Although TBI was phased out of production cars by the mid-1990s, many vehicles that employ the technology are still on the road. TBI is not the most efficient out of the three primary types of fuel injection systems, but it is still better than a carburetor. Switching from a carburetor to an EFI throttle body improves driveability and fuel economy, and TBI conversion kits are available for many older, carburetor-equipped cars.
TBI injectors spray fuel into the throttle body bore, right above the throttle plates. The air-fuel mixture then enters the intake manifold, where it is distributed to the engine's individual cylinders. 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), activates the TBI injectors.
Some users have expressed their preference for TBI vehicles, citing their reliability and ease of repair. However, others have criticised TBI for its lack of power and tuning.
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The throttle body controls airflow, while injectors control fuel flow
The throttle body and fuel injectors are two key components in an engine. An engine needs air, fuel, and spark to run. The throttle body controls airflow, while the injectors control fuel flow.
Throttle body injection (TBI) 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 there, the air-fuel mixture enters the intake manifold, which is distributed to the engine's individual cylinders. The throttle body portion of the assembly contains the throttle plates, idle air control valve, and throttle position sensor. The throttle body closely resembled a carburettor, with a fuel injector inside the throttle body.
In modern port-injected cars, the throttle body houses a throttle butterfly valve that lets in air, and the injectors add the appropriate amount of fuel. This happens outside the cylinder. In direct injection cars, the fuel is injected directly into the cylinder.
Some modern engines have both multiport injection (MPI) and gasoline direct injection (GDI) fuel injection systems. There is one of each type of injector per cylinder. TBI is found on older vehicles, and while it is not the most efficient, it is better than a carburettor.
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Direct injection engines inject fuel directly into the cylinder
Direct injection allows for more control during the fuel delivery process by atomizing the spray of fuel in the cylinder, providing better distribution of fuel throughout the combustion chamber. This also allows for the implementation of advanced engine management protocols such as Variable Valve Timing.
Direct injection engines inject fuel during the latter stages of the compression stroke, causing very quick (and inhomogeneous) mixture formation. This results in large fuel stratification gradients, meaning that there is a cloud of fuel with a very low air ratio in its centre, and a very high air ratio at its edges. The fuel can only be ignited in between these two "zones". Ignition takes place almost immediately after injection to increase engine efficiency.
Direct injection engines have some drawbacks. The most common problem associated with direct injection is the aggressive amount of carbon that builds up in the intake ports and on the back of the valves. This is because the previous method of fuel delivery, port injection, sprayed fuel in the intake ports, and the detergents in the gasoline helped keep these ports and valves clean.
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Conversion kits can update a carburetor to a TBI system
TBI systems use a dual-plane aluminium intake manifold and a throttle body with two injectors that deliver fuel to the engine. The injectors spray fuel into the throttle body bore, right above the throttle plates. From there, the air-fuel mixture enters the intake manifold, where it is distributed to the engine's individual cylinders.
Conversion kits are available for a variety of makes and models, and they usually employ TBI injection. Upgrading to a TBI system from a carburetor improves driveability and fuel economy, and provides a better driving experience overall.
For example, a '48 Ford sedan running a four-barrel-fed 327 small-block was converted to TBI using stock GM parts and a wiring harness from Painless Wiring. The assembly retailed for approximately $1,600, but careful boneyard scrounging could have found the same parts for hundreds of dollars less.
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Frequently asked questions
Almost all cars have a throttle body, which is used to control the amount of air entering an engine. In fuel-injected engines, the throttle body is located between the air filter and the intake manifold.
If your car has a throttle body, it likely also has fuel injectors. Fuel injectors are a part of the throttle body assembly, which includes the throttle body, throttle plates, idle air control valve, and throttle position sensor. Throttle body injection (TBI) was phased out of production cars by the mid-90s, but many vehicles that employ this technology are still on the road.
If your car is from the late 80s or early 90s, it may have a carburetor or a throttle body injection (TBI) system, which served as a segue between carburetors and multiport fuel injection. You can identify this by popping the hood and inspecting the engine.
