Under Pressure: How A Fuel Pressure Regulator Works With Boost

One of the most misunderstood fuel system components on a car is the fuel pressure regulator. The above video from Haltech does an excellent job explaining how the regulator functions.

Most people understand what this part does just by its name. You guessed it. The fuel pressure regulator regulates the fuel pressure. The regulator will keep the pressure at its predetermined setting, keeping the tune-up consistent and the engine happy.

Things get a little more complicated when you start adding boost. Let’s say your engine is operating at 45psi naturally-aspirated and you decide to add a ProCharger making 10-pounds of boost. The boost pushes back on the fuel system adding 10psi of pressure to the discharge-side of the injector. If your fuel system is set at 45psi, the injector will only emit 35psi of fuel to the cylinder, thus making the engine run lean. If we were to add 40psi of boost to the engine, the injector would only have a 5psi discharge from the injector.

The fix for this problem is the use of a fuel pressure regulator with a vacuum/boost port (often referred to as boost-referenced). This type of regulator has a 1:1 ratio meaning, as the regulator sees one pound of pressure, it will raise the fuel pressure by one pound to match. If you add 10 pounds of boost, the regulator will increase the rail pressure by 10psi taking it from 45psi to 55psi. The added fuel pressure will allow the injector to discharge a constant 45psi regardless of the boost pressure at the injector.

The regulator will also work in reverse as well. If the engine is pulling a vacuum, it will decrease the amount of fuel pressure accordingly to keep the ratio consistent. The engine vacuum will draw on the discharge side of the injector pulling more fuel through the injector, so it will decrease the pressure at the rail to compensate.

The result of a boost-referenced fuel pressure regulator is a constant flowrate across the injector regardless of the intake manifold pressure.

Be sure and check out some more informative videos from Haltech on their YouTube channel.

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About the author

Brian Havins

A gearhead for life, Brian is obsessed with all things fast. Banging gears, turning wrenches, and praying while spraying are just a few of his favorite things.
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