RDR 3000GT/Stealth Fuel Pump Rewiring Details

1. Fuel enters the inlet port of the fuel pump, which resides in your fuel tank, located below your spare tire.
2. Fuel is pushed through the pump and exits the outlet of the fuel pump under pressure. This pressure is determined by the amount of restriction presented to the pump by the rest of the fuel system. More restriction results in more pressure; less restriction results in less pressure. For most 3000GTs/Stealths, this pressure will be between 35psi and 70psi - more on that later.
3. Fuel flows through the hard metal lines on the underside of the car to the fuel filter, which is located on the firewall behind the battery.
4. After the fuel is filtered, it passes to the front fuel rail. The rubber hose between the fuel filter and the front fuel rail is easily accessible and a common/convenient place to locate a fuel pressure sending unit (gauge).
5. If the front bank fuel injectors (basically just an open/shut type valve) are open, some fuel will flow from the front fuel rail into the front cylinders (numbers 5, 3, and 1). The remaining fuel that does not flow out of the injectors will flow out of the other end of the rail into the crossover tube. If the fuel injectors are closed, then no fuel flows through those paths and all the fuel flows out of the other end of the front fuel rail into the crossover tube.
6. After passing through the crossover tube (a restriction of arguable importance), fuel flows into the rear bank fuel rail.
7. Fuel may pass through the rear cylinder fuel injectors (numbers 2, 4, and 6) if they are open, and any fuel that does not flow out of the injectors flows to the fuel pressure regulator.
8. The fuel pressure regulator is basically an adjustable-sized valve that presents a restriction to fuel flow. If the hole is narrowed, it restricts flow more than if the hole is widened.
9. Any fuel not consumed by the fuel injectors and allowed to pass through the fuel pressure regulator will flow back to the fuel tank and wait to be sucked up by the pump once again.

Things To Think About

• The fuel pump is a constant-flow type pump; you supply it a voltage and it starts flowing fuel. The pressure achieved is determined by the restriction to flow and the amount of fuel that leaves the system via the fuel injectors.
• If you apply less voltage to the pump, it will flow less fuel. If it flows less fuel, it will achieve less pressure in the lines, all else equal.
• The fuel pressure regulator is designed to maintain 43-45 psi of [differential] fuel pressure in the fuel rails under most conditions. Differential pressure just means that the pressure is referenced from the pressure in the intake manifold. That means that the pressure in the fuel rail should always be 43-45psi higher than whatever pressure exists in the manifold. Thus if the manifold pressure is -10psi (vacuum), the rail pressure will be 33-35psi (-10psi + 43psi = 33psi). Similarly if the manifold pressure is 12psi (boost), the rail pressure will be 55-57psi (10psi + 43psi = 55psi). Technical Note: in the numbers used above, I am not referring to MAP (manifold absolute pressure), but to the pressure typically displayed on a boost/vacuum gauge. Such gauges reference normal atmospheric pressure as "0".
• The fuel pressure regulator can compensate for reduced fuel flow rate by narrowing the orifice for the return line, but if it ever gets to the point where the return line is completely blocked off (orifice closed), that's all it can do - there's no more adjustment, and fuel pressure will fall accordingly.
• The fuel pressure regulator can compensate for increased fuel flow rate by widening the orifice for the return line, but if it ever gets to the point where the return line is completely unobstructed (orifice fully open), that's all it can do - there's no more adjustment, and fuel pressure will rise accordingly.
• At full voltage (12.0V or more), the stock fuel pump will flow so much fuel that, even with the regulator wide open (return line unrestricted), there will still be too much fuel flowing and the pressure in the lines/rails will be higher than desired. This is part of the reason that in a stock car, the fuel pump supply voltage is reduced to around 8.0V at idle (and low load) - this reduces the fuel pump output sufficiently such that the fuel pressure regulator can maintain 43-45psi in the fuel rails.

For More Information on Fuel Injection Systems in General