Fuel Pressure Regulator

The pressure regulator is a sealed unit which is divided by a diaphragm into 2 chambers (fuel and spring chambers). The fuel chamber receives fuel through the inlet side from the injector fuel rail. The spring chamber is connected to intake manifold vacuum.

At idle, when fuel requirements are low, the diaphragm is pulled down by intake manifold vacuum to allow excessive fuel to return to the fuel tank. As the throttle is depressed and fuel requirements increase, intake manifold vacuum decreases and diaphragm moves up shutting off the fuel return line to maintain constant fuel pressure.

On Toyota 4WD trucks and 4Runner, enrichment is necessary during 4WD operation. The ECU sends a signal to the fuel pressure regulator controlling solenoid to cut off the intake vacuum signal to the pressure regulator and increase fuel pressure. MR2 models use a similar system during air conditioner operation. Automatic transmission equipped models use this system to compensate for the load created by the torque converter.