Fuel Systems – Direct Injection

Fuel Systems – Direct Injection

The configuration of any GDI system will vary according to age and application.

Because gasoline direct injection was popularly introduced during the 1990s, the configuration of any GDI system will vary according to age and application. Nevertheless, as an overview, the heart of the GDI system is a low-resistance conventional magnetic solenoid injector or a piezoelectric fuel injector, a high-pressure mechanical fuel pump, a contoured combustion chamber and a modern air/fuel ratio sensor.

In contrast to the magnetic solenoid injector, the piezoelectric injector is composed of crystal wafers. When the wafers are electrically energized, they expand to produce the high mechanical pressures needed to open the injector pintle valve under 2,000 psi of fuel pressure. These crystal wafers are stacked in the GDI fuel injector so that they can nearly instantaneously pull the injector pintle valve open to admit fuel to the cylinder. Due to their design, operating voltages can range up to 90 volts at 15 amperes of current flow. Nozzles vary in design to ensure that the stream of fuel entering the cylinder conforms with the shape of the combustion chamber.

The high-pressure mechanical fuel pump, which is driven by one of the engine’s camshafts, is supplied by a conventional, single-line, in-tank pump. Fuel pressure on the mechanical pump is usually controlled by a pulse-modulated bypass solenoid mounted on the pump body.

Since direct fuel injection requires high fuel pressures to overcome combustion pressures created in the engine’s cylinders, a typical high-pressure fuel pump can produce in the neighborhood of 2,000 psi maximum fuel pressure, depending upon operating conditions. Fuel pressures are monitored by a high-pressure sensor located in the fuel rail and a low-pressure sensor located in the fuel supply line.

Modified combustion chamber design is another major feature of GDI systems. Keep in mind that the injector can be positioned in the center or to the side of the combustion chamber, or against the cylinder wall. Center-mounted injectors can use a cup-like recess in the piston to shape and contain the incoming fuel charge.

Similarly, side-mounted injectors can use channels and recesses in the piston head to help shape the incoming fuel charge. And, since the stratified or “lean-burn” modes can drastically increase piston temperatures, many GDI engines have oil nozzles mounted in the crankcase, underneath the pistons, to cool the piston domes.

You May Also Like

High-Pressure GDI Fuel Pumps

When solving a fuel pump issue, the scan tool is your best friend.

The most common diagnostic procedures for fuel pumps in the past were analog and hands-on, and most fuel pump-related problems could be solved with a pressure gauge and voltmeter. Today, the scan tool is quickly becoming the most important tool when diagnosing a fuel supply problem.

On early vehicles, the fuel pump was energized when the key was turned on and a vacuum-operated diaphragm regulated fuel pressure at the engine. Today, input from at least two modules and various sensors are required for a fuel pump to operate. This simplifies diagnostics and can save you from unnecessarily dropping a fuel tank.

Fuel Tank Contamination

A number of things can cause a fuel filter to plug up.

Oxygen Sensors And Catalyst Efficiency

Newer air/fuel ratio or wide-band sensors can detect a wide range of fuel conditions.

Gasoline Direct Injection Is Better, But Not Perfect

GDI technology has improved but drivers could face problems if they don’t keep up with maintenance.

Fuel Pressure Diagnostic Service

Use a scan tool that can look at special direct fuel injection parameters and perform bidirectional tests.

Other Posts
Alternators and Ripple Voltage

The alternator produces an AC current that must be converted into DC current by way of a rectifier.

Power Window Regulator and Motor Service

Power windows are great as long as they roll up and down when commanded to do so.

Dealing with Deposits to Boost Engine Life

Valvoline didn’t think an engine oil that removed deposits was possible … until they did it.

BMW Spark Plug Replacement

Here are a few things that you need to know before replacing spark plugs in a BMW.