AEM 30-71XX Infinity Stand-Alone Programmable Engine Mangement System Full Manual - Manual (Page 315)

Fuel System Setup 309
© 2014 AEM Performance Electronics
Fuel Pressure Regulator
The fuel pressure regulator maintains a constant pressure across the fuel injector. The inlet
manifold pressure varies with throttle angle, and engine speed. Small throttle angles and high
engine speed produce low manifold pressure (high vacuum). While high throttle angles and low
rpm give high manifold pressure. In addition to these conditions, low manifold pressure is
associated with idle and high manifold pressure is at full throttle. It is the fuel pressure regulators
job to keep a constant fuel pressure across the injector(s) regardless of manifold pressure.
Currently, there are several types of fuel pressure regulators in use. Many late model cars use a
return-less system where the fuel pressure regulator is mounted in the fuel tank adjacent to the
fuel pump (and therefore requires no return line back to the fuel tank). In most naturally aspirated
applications these types of systems are adequate. With forced induction or heavily modified
engines, an adjustable fuel pressure regulator with manifold vacuum reference must be fitted.
The two common types of fuel pressure regulators used are non-adjustable and adjustable. As
the name implies, a non-adjustable regulator is set at a fixed value and is manifold-vacuum
referenced (whenever a regulator is said to be vacuum referenced, this means that the inlet
manifold vacuum/pressure is ported into the chamber above the regulator diaphragm).
As manifold pressure increases, the pressure in the top chamber of the pressure regulator
increases along with it, allowing the regulator to compensate for the increased demand of the
fuel delivery system.
Keep in mind that at idle or low throttle openings with high rpm, there is very low manifold
pressure (vacuum). This tends to literally draw fuel from the injector. As manifold pressure
increases (as the throttle is opened), this vacuum dissipates and it is harder for the fuel to
discharge from the injector. The regulator reacts to the differences in manifold pressure to
maintain constant fuel pressure across the injector. There is a spring in the vacuum (top)
chamber of the fuel pressure regulator. The spring’s pressure on the diaphragm determines the