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 race cars 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 race car. 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 carburetor 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.

Fuel is pulled out of the fuel tank through a low restriction filter and pumped through a fine element filter to protect the injectors from any foreign particles. Fuel is delivered to the engine through special injectors mounted in the fuel rail. The fuel rail is pressurized by the fuel pressure regulator.* Excess fuel/pressure is bypassed through the regulator to the tank. The fuel pressure is set by adjusting the regulator. The proper fuel pressure is extremely important for top performance.