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The Difference Between GDI and PFI Engines

Manufacturers moved on from the original carburetor engines to single point fuel injection to overcome some drivability issues and problematic exhaust emissions. GDI and PFI engines are now the standard. But what's the difference and which is better?

GDI means Gasoline Direct Injection while PFI stands for Port Fuel Injection. There are two main differences between GDI and PFI.

Injector Location. As the name implies, a Gasoline Direct Injection engine injects fuel directly into the compression chamber. Port Fuel Injection on the other hand, injects fuel into the intake port.

Injection Pressure. While PFI injectors range from only 40-60 psi, a GDI injector has to work against combustion pressure and finish the injection much faster. So GDI fuel injection pressure can measure upward of 2,000 psi.

Which engine is the best?

Engines are powered by the combustion that occurs when a fuel/air mixture is injected into the compression chamber. The way this mixture gets there has a surprisingly large impact on fuel economy. PFI engines use a three-way catalytic converter, exhaust sensors and computer-controlled engine management to constantly adjust the fuel-to-air ratio injected into each cylinder. On the other hand, GDI engines inject directly into the cylinder. This way, most of the fuel is allowed to evaporate during the compression event. In short, this gains more control over the amount of fuel being injected and very little wasted fuel. The onboard computer accurately controls all these processes giving you more power with the same amount of fuel when compared to a PFI engine.

The Drawback of GDI

GDI systems have to be more sophisticated as the injectors must endure higher temperatures and pressure. Because of this, however, they are more likely to experience fuel system clogging and engine carbon build up. Fuel intake valves need to open and close quickly and smoothly, but carbon deposits can greatly restrict air flow and cause a host of issues.

Signs of intake valve buildup may include:

  • Loss of power/acceleration

  • Engine misfire

  • Lower fuel efficiency

  • Engine shaking

  • Jerking/vibration at stops

  • A lit “check engine” light

To help combat this, some manufacturers suggest regularly adding a fuel system cleaner to the vehicle. Some automakers have engineered specific fixes into their new models. But in the end, the best way to keep your vehicle running smoothly no matter the model is regular maintenance to see potential problems and keep all engine parts properly clean.

Don’t know what type of engine you have? Feel free to ask our lube techs. They are well trained to handle both PFI and GDI engines and will work with you to keep your vehicle in good condition.


Come on down to your local Shell Rapid Lube owned and operated by Flash Lube Oil! Your friends down here are happy to service your vehicle!

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