If you’ve tried to find the fuel pressure regulator on many late-model engines by looking in the engine compartment, you won’t find it there because the regulator has been relocated to the fuel tank. Engines with “returnless” electronic fuel injection (EFI) systems have the regulator inside the fuel tank. The regulator is part of the fuel pump assembly and is usually located downstream of the in-tank fuel filter.

Why have the vehicle manufacturers gone to this type of setup? To reduce evaporative (EVAP) emissions from the fuel system. In 2004, federal emission regulations required lower EVAP emissions. This, in turn, required a change to returnless fuel injection systems on many vehicles.

On a conventional port fuel injection system, fuel is routed to a fuel rail on the engine to supply the injectors. Fuel pressure is controlled by a vacuum-operated mechanical regulator mounted on the fuel rail. Intake vacuum is routed to the regulator through a vacuum hose and pulls against a spring-loaded diaphragm to maintain a preset pressure differential in the fuel system. When intake manifold vacuum is high, excess fuel pressure is vented through the regulator bypass valve and routed back to...