FAQ – EFI Regulators

After installing a larger (or secondary) fuel pump for my EFI engine, the fuel rail pressure went up and my regulator won’t adjust it back down, what’s wrong?

To understand this problem, it’s necessary to know that a fuel pump does not “put out” fuel pressure, it “puts out” fuel flow. A bypass regulator, correctly matched for a given flow volume, sets up a controlled restriction of this flow, thereby creating and then managing fuel pressure. If the regulator won’t adjust pressure down, verify it is large enough for the pump in use. Also, check the return line for kinks or obstructions and make sure the line size is adequate for it’s length and the flow it must handle going back to the tank. Remember, at low load (idle and cruise), the regulator and return line together must flow over 99% of the pumps volume. If the return line or the regulator, or both, are too small for the pump, the resulting fuel pressure is considered false-high. This means pressure is out of the regulator’s control and will drop to the actual regulator set point as the engine goes under load (WOT). A test for correct regulator and return line selection and function is to confirm pressure will adjust at least 5 psi lower than the desired base pressure, vacuum line disconnected.

Fuel is coming out of the vacuum/boost port on my regulator, why?
This type of leak indicates the diaphragm has either been ruptured or delaminated (lost it’s coating) and fuel is passing through it. Regulator diaphragms may be damaged by extreme pressures, chemical breakdown, or both. In some cases the regulator may be repaired, in others it will have to be replaced with a new model. Contact the Aeromotive tech department to discuss your options, including a discount trade-in program for out of warranty components.

I’m trying to plumb my stand-alone EFI regulator properly, where do I put the regulator, before or after the fuel rail(s), and what ports do I use?
Unlike a standard or “dead-head” carb regulator, which controls pressure between itself and the carburetor inlet, a bypass regulator creates and controls pressure between itself and the pump. Therefore, the correct EFI regulator location is after the fuel rail(s) whenever possible, promoting the required fuel pressure, flow volume and velocity through the fuel rail and to the injector inlet, at all times. Most Aeromotive EFI regulators have two inlet ports, one on each side, and one bypass port, on the bottom. Either inlet may be used with a single fuel rail engine, both inlets with a dual fuel rail. Any unused inlet ports must be blocked with the appropriate port plug. The ideal flow-path is: out of the fuel pump, into one end of the rail; out the other end of the rail, into the regulator side port(s); out the regulator bottom port, back to the tank at the top. Dual rail applications should employ a Y-block to split the supply line before entering the rails, then individual lines are run from the opposite end of each rail to each inlet port on the regulator.

I have a late model EFI engine equipped with a “returnless” fuel rail that I’m transplanting into another vehicle. I will be using an Aeromotive EFI pump and regulator but the fuel rail has only one connection port, how do I install the Aeromotive regulator?
In this case, the first and best option for a high performance application would be to purchase the correct, Aeromotive Billet Fuel Rail and install the regulator after the fuel rail, per FAQ 5 above. If a billet rail is not available for your application, the Aeromotive 13101 or 13109 regulator can be deployed before the stock fuel rail by using one of the regulator side ports as an inlet from the pump and the opposite side port as an outlet to the fuel rail connection. In this case, locate the regulator as close to the fuel rail inlet as possible and route the return line back from the bottom port back to the top of the fuel tank. Check out Aeromotive’ line of specialty/OEM adapter fittings to facilitate converting the stock fuel rail to the appropriate AN line.

I want to connect a wet nitrous kit to my EFI engine, can I use the fuel pressure port on my Aeromotive regulator to supply the nitrous/fuel solenoid?
Normally, this is not recommended. The gauge port on most Aeromotive regulators is designed as a passage for sampling regulated pressure, and may not support adequate, regulated fuel flow. The typical bypass EFI fuel system can be tapped anywhere between the fuel pump outlet and regulator inlet. For best fuel pressure control to the nitrous fuel solenoid, connect the nitrous fuel supply line by inserting a “T” fitting to one of the fuel lines coming out of the fuel rail, before it connects to the regulator. This “T” fitting should be placed as close to the regulator inlet port as possible. With higher HP nitrous systems, consider a dedicated nitrous fuel system to provide the fuel flow and pressure control desired for best, safe nitrous system performance.