AEM 30-6905 Universal Programmable EMS-4 - Manual (Page 140)

Page 140 of 279 EMS-4 Install and Tuning Guide_Rev 1.6
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
f
uel system‟s static pressure. The system‟s static pressure is the amount of pressure measured
with the vacuum hose disconnected or with the engine turned off. The fuel system‟s static
pressure is higher than the fuel pressure at idle or under high vacuum conditions.
When the engine is running, the engine vacuum acts against the spring and the effect of the
vacuum diminishes as the throttle is opened. At idle, there is a high amount of fuel returned to
the tank because the vacuum is pulling the diaphragm seat off of the fuel return orifice, reducing
fuel pressure. As the throttle is opened, the diaphragm seat starts to close off the orifice,
restricting the amount of fuel flow through the return line.