Accel/dfi – Mallory Ignition ACCEL CHEVROLET APPLICATIONS (including LT-1) 74022 User Manual

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ACCEL/DFI

climates. Boost pumps used on such vehicles as a 1985 Ford
F-250 5.0L EFI will work well for this type of application. The
switching valve from a 1984 Ford 6.9L Diesel or a 1986
Chevrolet C-10 (305 CID) will work well in dual tank appli-
cations. Dual tank equipped vehicles must be plumbed to
return excess fuel to the tank which is supplying fuel to the
EFI system to avoid tank overflow problems. The remotely
activated dual tank three way valves described above will
work well in these applications.

A NOTE TO THE INSTALLER

There seems to be a misunderstanding with some people
that a fuel pump “produces pressure”. This is wrong. What
actually happens is the pump produces fuel flow at a given
system pressure which is dictated by the pressure regulator.
The pressure regulator has a spring which is preset to
provide a certain system pressure, i.e. 45 PSI. The regulator
opens as the pressure in the fuel line increases due to the flow
of fuel provided by the pump.

As the pressure drops, due to bypassing of fuel to the tank,
the regulator closes at a pressure of 45 PSI (this pressure is
variable on adjustable regulators). This process will begin
again as pressure raises. Therefore, the pressure regulator is
a dynamic modulating device which is always trying to seek
its preset pressure.

Sending Unit Modifications

To install a return fuel line in your tank, remove the sender
assembly from the fuel tank and drill a 5/16” hole through
the top of the flange. Be sure to give yourself enough room to
weld the tube into place; welding procedures are discussed
later in this section. ACCEL/DFI Jumper Line Kit, Part
Number 74731, will supply you with the this line as well

with other lines that you may need. Pre-bend a piece of
5/16” fuel line so that the in tank portion end is 2” from the
bottom of the tank and away from the existing outlet tubes
(see figure H). Ensure that the installation of this line does
not interfere with any other components on the tank unit.
Clean the unit with soap and water prior to the next step.
Seal and secure the return line to the flange by welding or
brazing with low heat so that flange warpage does not occur.
Also make sure that applied heat does not damage the send-
ing unit wires or wire seals. Clean the welded area and check
for cracks or holes in the flange, tubes or welded area.

Check the condition of the filter sock on the pick-up tube. If
the sock is torn or contaminated, replace it. Again, if you are
not using a filter sock in your application then install a filter
between the fuel tank supply line and the inlet side of your
fuel pump.

Return Fuel Line Installation

If your vehicle was originally equipped with a carburetor,
you MUST run a 5/16” diameter or larger return line from
the engine (fuel pressure regulator) to the fuel tank. Some
vehicles with carburetors came with 1/4” diameter return
lines. This line is too small in I.D. and will create an
unacceptable amount of back pressure in the fuel line, thus
causing a rich condition. Using good judgment install a fuel
line from the pressure regulator outlet to the fuel tank with
restriction free bends in protected areas (refer to figure H).
The fitting at the pressure regulator is a #5 AN fitting and
ACCEL/DFI recommends a #5 AN to 5/16” Aeroquip stain-
less fuel line connector to connect the 5/16” return fuel line.

ACCEL/DFI recommends using a good fuel line for supply
and return line plumbing, such as a double braided stainless
steel AQP by Aeroquip.