A Closer Look: Gasoline Direct Injection (GDI) – UnderhoodService

A Closer Look: Gasoline Direct Injection (GDI)

Sponsored by Standard®

Gasoline direct injection (GDI) is used on most new vehicles and requires a different approach to diagnosis and service. GDI technology has been an integral part of helping to improve fuel economy while reducing emissions, and can be found on more than half of the U.S. fleet. In fact, the use of GDI engines has grown by over 600% since 2010. This means that in the next five years, 42 million more vehicles with GDI will enter the Aftermarket “Sweet Spot” of 6-12 years old, during which their injectors and related parts may need to be serviced or replaced. While GDI systems have proved effective, these systems encounter specific failures and require an understanding of how they work and how to test them when they set a code.

Why GDI?

In order to meet tighter emission and CAFE (corporate average fuel economy) standards, manufacturers began introducing GDI engines in the early 2000s. The fuel injectors on a GDI engine inject fuel directly into the combustion chamber primarily on the intake stroke and, in some cases, on the compression stroke as well. As engine speed increases, the amount of time available to inject fuel decreases. Fuel pressure is increased to help increase fuel delivery in a shorter amount of time, producing more power. Fuel rail pressure typically ranges from 300 PSI at idle to 2200 PSI at full load.

Above is a typical GDI fuel system layout. A low-pressure fuel pump is located in the fuel tank. The low-pressure pump supplies a camshaft-driven mechanical high-pressure pump with 50-80 PSI of fuel. The mechanical pump then generates the high pressures needed and delivers the high-pressure fuel to the fuel rail. The amount of pressure generated in the fuel rail is determined by an ECM-controlled fuel volume solenoid, which is typically part of the mechanical pump. 

Tech Tip: When removing the high-pressure fuel pump for any reason, check the follower for wear. If the follower is pitted or chewed up, the camshaft will likely need to be replaced.

The amount of fuel pressure that the pump generates in the fuel rail is dependent on how much low-pressure fuel is allowed to flow into the high-pressure pump. The flow into the pump is controlled by the PCM-controlled integral fuel regulator. In order to deliver high-pressure fuel to the fuel rail, the regulator valve must be timed to the camshaft lobes. This is accomplished by monitoring camshaft position sensor input from the camshaft that drives the high-pressure pump. If there is a problem with the pump, it is important that the technician replace the follower and lines at the same time, and inspect the camshaft. 

Tech Tip: Many GDI pumps are known to leak gasoline into the engine when they fail. This can cause fuel trim issues (due to excess fuel getting into the PCV system) or engine failure due to dilution of the oil. Always inspect the oil and change it after a pump failure.

Servicing GDI

Prior to servicing components on a GDI fuel system, it is crucial that there is no pressure in the fuel system. Some vehicles can be depressurized using a scan tool command to the ECM, while others will require the removal of the low-pressure pump fuse or relay. The vehicle should then be started and idled until it runs out of fuel and dies. 

Before disassembling a GDI fuel system for service, it is important to read service information. Most high-pressure fuel lines are a one-time-use component. When they are torqued down, they will distort to fit, ensuring a tight seal. In the above example, you’ll see a GM 3.6L V6 with the intake manifold removed. Note the yellow tags on the high-pressure lines indicating that they must not be reused. Other manufacturers may not use labels, instead recommending within the service information to discard these lines after removal. Reusing these lines can result in a high-pressure fuel leak which could cause a catastrophic fire. 

The service information will also help to identify all of the tools necessary to complete the task of replacing the fuel injectors. Once components such as the intake manifold have been removed in order to access the fuel rail, it is important to note that there are two basic types of injector-to-fuel-rail connections. 

Tech Tip: Extreme caution should be used when removing the fuel rail. The rail and injectors can be damaged by attempting to pry the rail out incorrectly. Equal pressure should be applied to all areas of the rail at the same time. Videos explaining how to do this properly can be found on our StandardBrand YouTube channel.

On some applications, the fuel injectors are clipped onto the fuel rail. When removing one of these fuel rails, the rail and all of the injectors will come off the engine in one piece. 

Standard® GDI Injectors are precision engineered and rigorously tested to ensure optimal performance.

Standard® GDI Injectors are precision engineered and rigorously tested to ensure optimal performance. 

On applications that do not use a retaining clip, you may find that some of the fuel injectors remain in the cylinder head while the rest come out attached to the fuel rail. With the fuel injectors removed, be sure to clean the ports in the cylinder head with a correctly sized wire brush and replace the seals on any fuel injectors that are to be reused. Complete the installation by using the appropriate torque specification and tightening procedure. 

Standard® GDI Injectors are always new, not remanufactured.

Standard® GDI Injectors are precision engineered and rigorously tested to ensure optimal performance. 

On applications that do not use a retaining clip, you may find that some of the fuel injectors remain in the cylinder head while the rest come out attached to the fuel rail. With the fuel injectors removed, be sure to clean the ports in the cylinder head with a correctly sized wire brush and replace the seals on any fuel injectors that are to be reused. Complete the installation by using the appropriate torque specification and tightening procedure. 

Blue Streak® Direct Injection High-Pressure Fuel Pump Kit (GDP204K) for 2019-11 Ford and Lincoln SUVs, trucks and vans. VIO: 1.5 million

In 2023, Standard® Blue Streak® launched its new line of Direct Injection High-Pressure Fuel Pump Kits. These new Kits simplify fuel pump replacements by including everything needed for a complete repair: a high-pressure fuel pump, camshaft follower, O-ring, and any additional components needed based on the individual manufacturers’ repair procedures. Providing these components in a complete kit saves technicians’ time and ensures that the job is done correctly the first time with all-new parts — no chasing the correct parts or replacing remanufactured parts that arrive defective. 

Standard’s GDI line-up includes hundreds of part numbers for domestic and import vehicles, including applications through 2023, providing industry-leading late-model coverage. To learn more, visit www.StandardBrand.com.

For tips on replacing GDI components, search “GDI” on the StandardBrand YouTube channel.

This Article is Sponsored By: Standard®

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