Mallory Ignition 4110, 4150, 5250 User Manual

ELECTRIC FUEL PUMP
TROUBLESHOOTING GUIDE

The following pertains primarily to Mallory COMP Pumps
equipped with Gerotor style pump systems, but also
applies to many other fuel systems.

BASIC INFORMATION

The Mallory Gerotor style COMP Pumps are more forgiving
than vane style pumps, but it is still important to insure
they are properly mounted and receive clean fuel.

The correct mounting position is even with or below the
tank and preferably behind or next to the fuel tank. All
electric pumps push fuel far better than they can pull
(suck) fuel.

Make sure that a low restriction filter is between the tank
and the pump. A 40-micron element it sufficient to pro­tect the pump from contamination such as dirt, rust, fuel
cell foam, etc. Mallory has them available that will screw
directly into the pump itself.

Electric pumps need a clean and stable power source. Run
a minimum of 12 gauge wires to the pump if it is relatively
close to the power source. Longer runs should utilize 10
gauge wire instead. With a trunk-mounted battery, we
recommend that you use a relay to allow for short power
wires to be run. Do not pull power from a common termi­nal, especially if the
ignition is wired to the same terminal.

The regulator used must be properly matched to the flow
characteristics of the fuel pump. Refer to the compatibility
information in the current Mallory Catalog. Small regula­tors and big pumps don’t work. Also, check to make sure
the pump and regulator are designed for the type of fuel
that is going to be used.

For the longest possible life from your Mallory or
any other brand of electric fuel pump, it is highly
recommended that you use a bypass style regulator.
This allows the pump to run cooler, keeps the fuel cooler
reducing the chance of vapor lock, draw less amperage,
and supply constant flow of fuel. The minor inconve­nience that running a return line to the tank presents is
more than offset by the positives mentioned above.

Fuel line size is based on the length of the lines in
addition to the intended use. The supply line to the
engine is based on the horsepower of the engine. The

return line size is based on the total volume of the fuel
pump. Basically, to insure stable fuel pressure, the
return line should be of sufficient diameter to handle
the full volume of the fuel pump without the engine
running. That means that the return should be as big
or bigger than the supply line.

Use liquid thread sealing or a suitable pipe dope and
not thread sealing tape on all threaded fuel systems
connections. Pieces of the tape can break off as they
are being assembled and plug up lines, get stuck on
small passages, and even seize up a pump if they are
large enough.

Don’t buy cheap fittings. Use low restriction fittings, pref­erably CNC machined ones like those listed in the Mallory
catalog. Tightly angled fittings can be just as bad of a
restriction as too small of a line size. The larger the radius,
the better and make sure that you buy quality fuel lines.
Look at them closely and make sure they have a large
inside diameter. That especially applies to some of the
low cost dual feed lines being sold today. Some 3/8” OD
lines are 1/4” or less ID.

FREQUENTLY ASKED QUESTIONS

Q.- Why can’t I adjust my fuel pressure down? Even with

the adjuster backed all of the way out, I still have too
much.

A.- Start by checking to make sure the regulator is suit-

able for the pump you have installed. Next, if it is a
bypass system, check the return line size. If the return
line is too small, the regulator isn’t causing the pres­sure, rather it’s the return line size is too small. This
is especially a problem when the factory return line is
used. Ford Mustangs are probably the most common
offenders.

There are a couple ways to prove it. The easiest way is
to remove the spring from the regulator. Without start­ing the engine, turn on the pump. The pressure gauge
must read less than 3 PSI on a carburetor-equipped
engine and less than 10 PSI with high-pressure fuel
injection.

Q.- When I first hit the throttle hard, the pressure drops

then comes back up. Why?

A.- The pump has to catch up to the demand. The

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problem would not exist if the car had a return
(bypass) style regulator. The fuel would always
be flowing.

Q.- When I adjust the fuel pressure, it’s fine when it’s cold,

but then it starts dropping off. If I let it cool off, the
pressure comes back up. If I readjust it hot, then I
have too much pressure cold. What’s going on?

A.- This is a classic problem when there is a liquid filled

gauge mounted on or near the engine. The pressure
isn’t changing, it’s the gauge reacting to the under­hood temperature. To prove it, start the engine with
everything cold, then blow hot air from a hair dryer on
the gauge. You can watch the pressure reading drop.
It’s just the nature of liquid filled gauges and hot
engines. Try to mount the gauge away from as much
engine heat as possible.

Q.- I want to run a return style system, but there isn’t

another hole in the tank. What can I do short of weld­ing in a fitting. Can I dump it back into the feed line?

A.- Run the return into the fill neck if you have to, but you

cannot either put it into the feed line or the bottom of
the tank. Remember to keep the return line above the
fuel level in the tank.

pump gas. Racing type gasoline
evaporates quickly and leaves a sticky mess that will
gum up everything. Just remember to put the right
fuel in before you go out and stand on
the throttle.

Q.- I took my pump apart, cleaned it up and tighten it

back up. Now it doesn’t want to run. What did I do
wrong?

A.- When you put the pump assembly back on the bot-

tom of the motor, be sure to draw both of the screws
up slowly and evenly. Do not over tighten them.
Make sure all of the pieces go back on the same way
they came off. Putting a grease pencil mark down the
side of the pump housing is the simple way to make
sure that you don’t put it together backwards. They’ll
fit, but they won’t flow the fuel right.

Q.- Every Spring, I have to take apart my pump and regu-

lator apart. I store my car in the winter in a garage.
Why the sticky mess?

A.- The higher octane the gas, the quicker it

evaporates. If you leave fuel in the system, add one
of the many additives available and put in a regular

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