TBI Fuel Injection: Pros and Cons of Throttle Body Fuel Injection

April 5, 2012

Learn what TBI fuel injection is, its benefits and drawbacks, and tips for increasing the fuel efficiency of throttle body injection.

Engine With TBI Fuel Injection

TBI fuel injection is a type of fuel injection system where the fuel is injected into the throttle body. The throttle body fuel injection system, or TBI as referred to by GM or CFI by Ford, works using a single or pair of injectors. The throttle looks like a carburetor without the fuel bowl, the metering jets or the float.

This type of fuel injection system consists of only two major castings - the fuel body and the throttle body. The fuel body supplies the fuel while the throttle body has a valve that controls the flow of air. On the throttle, there are ports that gather signals to relay to the manifold absolute pressure sensor and to the emission control system.

There are advantages and disadvantages in using the throttle body fuel injection system. Determining which weighs more will depend on what you need for your car.

TBI Fuel Injection Advantages

  • It is less expensive than using other types of fuel injection systems.
  • It is easier to clean, maintain and service because there are fewer parts.
  • It is cheaper to manufacture than a port injection system and simpler to diagnose. It also does not have the same level of injector balance problems that a port injection system might have when the injectors are clogged.
  • It greatly improves the fuel metering compared to a carburetor.
  • You do not have to make any changes to the TBI intake manifold. You also do not have to change the throttle linkage. Instead, use the existing linkage, air cleaners and carbs to install the system.
  • It is also capable of logging data and can be programmed for ignition and fuel. The TBI system is that it learns and understands your habits when driving so it can easily map out your actions and the performance of the engine.

TBI Fuel Injection Disadvantages

  • It is almost the same as a TBI carburetor wherein the fuel is not equally distributed to all the cylinders. This means that the air/fuel mixture injected differs for each cylinder.
  • It can cool the manifold much faster causing the fuel to puddle and condense in the manifold. The possibility of condensation is much higher since the fuel travels longer from the throttle body to the combustion chamber.
  • Since the system needs to be mounted on top of the combustion chamber, you're prevented from modifying the manifold design to improve your car's performance.
  • It is a wet system and the mixture of fuel is still based per cylinder.

Engine Fuel Injection Fuel Efficiency Tips

The majority of modern cars employ fuel injection. It provides instant throttle response and improved fuel efficiency. Cars once utilized a carburetor, which were easy to clean and adjust; however, they dumped gasoline into the engine and sometimes had cold weather drivability issues. In the 1980s, throttle body fuel injection became widely used, but it was more or less an electronic carburetor. Cars today use individual fuel injectors for each cylinder, making fuel delivery far more precise with improved fuel economy. An onboard computer is able to adjust fuel delivery based on engine needs, which in turn reduces fuel consumption and lowers emissions.

One of the easiest ways to get more MPG from your fuel injection is to modify driving habits. For instance, take off slowly from stops. Taking off quickly wastes gasoline. Coasting to a stop is another way to increase fuel economy because the car is already moving and the engine requires far less fuel.

Another way to increase MPG and reduce fuel consumption is to use only high quality fuels. Low quality fuels can increase engine and fuel system deposits and reduce the efficiency of fuel-injected engines. Performing routine maintenance as outlined in the owner's manual is also important for maintaining fuel economy; tune-ups, oil changes and replacing the air filter will all help to increase MPG. Although most car manufacturers indicate they are not necessary, there is a marketplace full of fuel injector and fuel system cleaners designed to reduce buildup and increase gas mileage.

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