In fuel injection systems two of the major components are fuel injectors and the fuel injection computer. Fuel injectors are solenoid valves that are controlled by the fuel injection computer. The computer causes the injectors to quickly open and close when the intake valve is open and drawing air into the cylinder. The amount of fuel delivered depends on the injector flow rating (pounds per hour or cc per minute), the length of time the injector is open (pulse width) and the fuel pressure. Fuel injectors are available with a variety of spray patterns for different applications. Some spray patterns are good for economy and others are better for maximum power at high RPM. Fuel injector placement and alignment are also very important factors for producing maximum power. For high RPM engines the alignment is even more important, as the injector has less time to deliver the fuel load while the intake valve is open.

Fuel pressure is one of the most crucial settings when working with a fuel injection system. Improper fuel pressure is a leading cause of poor performance in a fuel-injected engine. The fuel pressure setting directly affects the air/fuel mixture. Automotive systems are “closed loop” while current motorcycle systems are “open loop”. In a “closed loop” system, oxygen sensors provide feedback about the air/fuel mixture and the system adjusts automatically. In an “open loop” system there is no feedback to the computer. This means that if the fuel pressure is not properly set, the computer has no way of knowing the pressure and the air/fuel mixture will be affected accordingly.

Unfortunately, it is relatively difficult to measure fuel pressure accurately. Fuel pressure gauges commonly used in racecars come off of the line with an accuracy of +/- 2% of full scale. In addition to the inherent inaccuracy of the gauge, calibration is affected by impact such as those experienced in a racecar. In-car fuel pressure gauges should only be used as indicators, not as reference instruments for calibrating fuel pressure. Fuel pressure should always be set using a reference gauge that is temporarily attached for measurement.

In order to achieve top performance, component placement and fuel flow through the fuel injection system is important. Since the fuel pressure is much higher than in a carbureted system, the proper selection of fittings, tubing, filters, regulators, and pumps is imperative. The fuel flow should come from the fuel tank, through the primary filter to the fuel pump, then through the secondary filter to the fuel rail, then through the regulator and back to the tank. In order for the system to function properly it's important for the fuel pump to be placed below the fuel level in the tank. Fuel injection pumps are very good at pushing fuel, but they are very poor at pulling fuel. The filter between the tank and pump should be free of any restrictions. For consistent fuel pressure, the regulator should be placed as close as practical to the fuel rail.