Kyle Bennett writes:

I was wondering if someone could explain how a fuel pressure regulator works?

I have been told it will increase the amount of pressure in the fuel rail, which inhand makes it capable of injecting a little more fuel than the stock injectors would normally inject. When you install this regulator in-line, what is it that actually increases the fuel pressure? It looks to me as if fuel goes in and fuel goes out like a "Tee". I realize the set screw on top regulates the pressure, but how? Is there an impeller inside or something??? I'm at a loss on this, could someone explain??

Kyle Bennett



Most modern fuel injected cars run a fuel pump in the tank and run much more fuel than is needed to the fuel rail. A regulator keeps a certain amount of fuel pressure in the rail and then sends the rest back to the tank.

Your car as well as most fuel injected cars have a one to one fuel regulator. It varies the fuel pressure by 'watching' manifold pressure. It uses a diaphragm to control pressure. Most Nissans at idle (vacuum) fuel pressure is 34psi and at full throttle (No vacuum in theory) 43psi. If you further put pressure (turbo or super charger) to the manifold, it further increased fuel pressure. In factory regulators, for every pound of boost, it adds a pound of fuel psi. Hence 1 to 1.

Most adjustable regulators are still one to one or close to that, however you can adjust the pressure at idle or full throttle for fine tuning. There is one other type of regulator that is used with aftermarket forced induction. These are rising rate regulators commonly called FMU's (fuel management unit). These regulators increase fuel pressure at a multiplication factor of boost. So instead of messing with complicated computers and injection duty cycles, these systems just increase fuel pressure to add fuel. They go inline down from the factory regulators and only start to add pressure under boost. So when you are off boost, you maintain factory tuning and drivability. Only as you get boost does the FMU begin to increase fuel pressure.

Hope that helps,

Mike Lee

93 S13 turbo


We haven't done it yet, but we're needing to check our Fuel Pressure Regulator. We don't own a hand vacuum pump and a fuel pressure gauge and are hesitating  to just change the regulator over investing in the 2-tools. We'll get over it soon and spring for them. We're just struggling for now. :)

It's mounted on the end of the fuel rail towards the rear of the engine on the side the injectors are on. There are 2- little bolts holding it on the fuel rail.

To check:

Release the fuel pressure in the system by removing the Fuel Pump fuse and start the engine. After it stalls, crank it a few more times to release the fuel pressure.

Install the fuel pressure gauge on the inlet side of the pressure regulator, start the car and check for fuel leaks.

At idle, the pressure should be approximately:

235kPa / 2.4 kg/cm2 / 34 psi.

Disconnecting the vacuum hose, you should see:

294 kPa / 3.0 kg/cm2 / 43 psi.

After getting your yah-yahs out over that test, connect a hand vacuum pump to the regulator and start the engine. As the vacuum INCREASES, the fuel pressure should DECREASE. If this is not the case, time for a new pressure regulator.

Let us all know what happens,
'91 S13