INSTALLATION INSTRUCTIONS
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W W W . A T O M I C E F I . C O M
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RETURN STYLE FUEL SYSTEM
If you have decided that a returnless fuel system will not produce the best performance for your
application, you will need to route a return line in the fuel system. There are many aftermarket fuel
regulators available. The fuel can then be routed to the sending unit of the gas tank, or even the filling
port of the tank. This will take modification. Figure 2 shows an example of a return style fuel system.
The most efficient system is to return the fuel from the opposite outlet of the throttle body.
The fuel pressure required for a return fuel system is approximately 45psi. If the pressure is not enough
the injectors will be over-worked and an “INJ DC” code will appear in the Diagnostics on the Handheld.
If this happens increase the fuel pressure by 5 PSI increment and test again. A rule of thumb is to start
at approximately 60 psi for engines over 400 horsepower.
With a return style system you must connect the fuel lines as pictured below. Connecting them
like in the lower picture can cause fluid hammer inside of the throttle body on transient operations. This
will cause hesitatons and possibly dead zones at certain RPM ranges.
DANGER
CAUTION
WARNING
NOTICE
FUEL TANK
FUEL
PUMP
AFTERMARKET
ADJUSTABLE
REGULATOR
PRE FUEL
FILTER
FUEL TANK
FUEL
PUMP
MSD ADJUSTABLE
REGULATOR
POST
FUEL
FILTER
PRE FUEL
FILTER
NOTE: Do not use tubing (hard fuel lines) with the Atomic EFI system.
FUEL TANK
FUEL
PUMP
AFTERMARKET
ADJUSTABLE
REGULATOR
PRE FUEL
FILTER
FUEL TANK
FUEL
PUMP
MSD ADJUSTABLE
REGULATOR
POST
FUEL
FILTER
PRE FUEL
FILTER
INCORRECT
CORRECT FOR RETURN STYLE FUEL SYSTEM.
Figure 2 Atomic Return Style Fuel System.
