|
This page will educate my
viewers to the sometimes elusive fuel system problems that many of us
encounter...
This page is a Question and Answer session that should assist you in
diagnosing fuel system problems with your race as well as street vehicles.
Enjoy!!!
|
|
| Q |
You're using a dead-head regulator
on a 450 HP motor. What is the smallest Mallory fuel pump you should use? |
| A |
Multiply
horsepower by .23 (450 x .23 =104 GPH). Mallory's
110 pump is a lower volume pump and therefore can be used with a
dead-head regulator on this application, but it is very close to the
actual demand. Because of this, a Mallory
140 GPH pump should be used. |
| Q |
You're using a return-style
regulator on a 450 HP motor. What is the smallest Mallory pump you
should use? |
| A |
Multiply
horsepower by .17 (450 x .17 = 76 GPH). The next larger
pump is a Mallory 110, but this pump is not designed to work on
return style systems. It is best to use the Mallory 140 GPH fuel
pump. |
| Q |
A 450 HP engine and a 140 GPH pump.
What is the minimum fuel line size from the pump to the
regulator? |
| A |
1/2" or -8
AN |
| Q |
A 450 HP engine and a 250 GPH pump.
What is the minimum fuel line size from the pump to the
regulator? |
| A |
1/2" or -8
AN (Remember, fuel line size from the pump to the regulator is
determined by horsepower, not fuel pump size.) |
| Q |
A 450 HP engine, a 140 GPH pump and
a return regulator. What is the minimum return line size? |
| A |
1/2" or -8
AN (Return line size is decided by fuel pump output). You want to
have zero or negative pressure on the return line for optimum
performance and accuracy. |
| Q |
A 450 HP engine, a 250 GPH pump and
a return regulator. What is the minimum return line size? |
| A |
5/8" or -10
AN (Again, return line size is determined by pump size,
regardless of horsepower.) |
| Q |
You have a 450 HP street car and DO
NOT want to purchase a fuel pressure regulator. What Mallory pump should you use? |
| A |
450
HP x .23 = 104 GPH. The next biggest pump is 110 GPH. The 110 GPH
pump is a low pressure pump and can be used without a regulator.
(Not my first choice for optimum power and safety!) |
| Q |
You now decide to Drag Race your
450 HP street car with the 110 GPH pump and no regulator. At the
track your fuel pressure drops from 7 PSI to 3 PSI during a pass.
What can you do? |
| A |
First,
do not call Us or Mallory's tech line and say the pump is defective!
In general, an electric fuel pump should always be used with a
separate pressure regulator when racing. The 110 GPH pump is a low
pressure pump so you have (3) options:
- Reduce the pressure drop by increasing
fuel line size. This will help, but more than likely will not
cure the problem.
- Add a return-style regulator and a return
line to the system after plugging the bypass in the pump.
- Replace the 110 GPH pump with the high
pressure and volume 140 GPH pump and a dead-head regulator. (A
return style regulator is recommended)
|
| Q |
You have a 140 GPH pump and a
dead-head regulator. When you suddenly jump on the throttle (or hit
a Nitrous 
button), the pressure drops 3-4 PSI and then comes back up in about
a half-second. What's wrong? How can this problem be reduced? |
| A |
The temporary
drop in pressure is due to the recovery time of the regulator. Using
a very large fuel pump along with a very high bypass pressure may
help. However, the use of a return-style regulator is your best
cure. |
| Q |
I have a dead-head regulator and it
will not adjust above 4 or 5 PSI. What's wrong? |
| A |
There are (3)
possibilities:
- You are trying to adjust the pressure without the
engine running.
- The pump is only producing 4 or 5 PSI (the pump is a
low pressure type or the bypass is malfunctioning).
- The regulator is malfunctioning.
|
Some more ...
| Q |
You have a dead-head regulator and
it will not stay at the pressure you set it at. The pressure slowly
increases, especially at idle. What's wrong? |
| A |
Well, this one
gets you (4) possibilities:
- You're trying to adjust the pressure without the engine
running.
- Pressure creep. This is common with dead-head
regulators. If there is an O-ring on the plunger of the
regulator, make sure it is undamaged.
- The diaphragm in the regulator is leaking. Remove the
top of the regulator and check the diaphragm. It should be dry
on top.
- The bypass in the pump is stuck and the pump is
producing excess pressure. Install a pressure gauge just before
the regulator and verify pump pressure.
|
| Q |
You are using an electric fuel pump
and a dead-head regulator. During full throttle acceleration, the
pressure gauge gradually drops before you lift. What's wrong? |
| A |
Here are some
possibilities:
- The fuel pump is too small ... (multiply HP x .23)
- The fuel pump is not supplying the rated fuel volume.
Connect a short hose to the outlet of the pump and fill a gallon
bucket. A 70 GPH pump should flow at least 1 GPM (gallon per
minute); a 140 GPH pump should flow 2.1 GPM; a 250 GPH pump
should flow 3.75 GPM; a 500 GPH pump should flow 7.5 GPM. (NOTE:
This test should be run with a battery charger on the
battery since the engine will not be running, utilizing the
alternator to help sustain amp load.)
- The fuel pump is not getting adequate power supply of
at least 12-volts. Splice a voltmeter into the power wire (red
wire on Mallory fuel pumps) near the pump. With the pump
operating and the engine running at approximately 2000 RPM,
there should be 12-14 Volts at the pump. If not, use larger
wires, a fuel pump relay, or a better charging system.
- The fuel pump bypass pressure is too low. Connect a
pressure gauge just before the regulator . At idle, the pressure
should be at least 3 PSI higher than the set pressure of the
regulator.
- Too much restriction in the fuel lines. At full
throttle, the pressure just before the regulator must stay
higher than the set pressure. It it doesn't, there is too much
restriction in the fuel lines and fittings, or the pump is too
small.
- Fuel filter(s) are too restrictive or clogged
- Too much restriction between the fuel tank and the fuel
pump.
- The fuel pump is "sucking air". Check the
pickup in the fuel tank and the fittings between the tank and
the fuel pump. If fuel coming out of the pump looks
"milky", there is air entering the system. Air can be
drawn in from a fuel tank pickup that is too high, low fuel
level in the tank, and around the fuel fittings (even though fuel
will not be leaking out).
- The regulator diaphragm is damaged. The top of the
diaphragm (inspected upon disassembly) show be dry.
- The fuel pump is "losing prime". Ideally you
want to mount the fuel pump level with the bottom of the fuel
tank, and as close to the tank as possible. Otherwise G-forces
may cause the pump to lose prime. (NOTE: The #1
cause of "burning up" a fuel pump is due to its losing prime. The fuel running through the pump is actually
keeping it cool.) Having a fuel cell or sumped fuel tank can
cure most prime issues as long as the pump is not mounted too
high.
|
| Q |
You are using an electric fuel pump
and a return style regulator. During full throttle acceleration, the
pressure gradually drops until you lift. What's happening? |
| A |
Here are some
possible problems:
- The fuel pump is too small (multiply HP x .17)
- The fuel pump is not supplying the rated volume.
Connect a short hose to the outlet of the pump and fill a gallon
bucket. A 70 GPH pump should flow at least 1 GPM (gallon per
minute); a 140 GPH pump should flow 2.1 GPM; a 250 GPH pump
should flow 3.75 GPM; a 500 GPH pump should flow 7.5 GPM. (NOTE:
This test should be run with a battery charger on the
battery since the engine will not be running, utilizing the
alternator.)
- The fuel pump bypass has not been plugged or disabled (NOTE:
All Mallory return regulators include instructions on how o
disable the bypass in a Mallory fuel pump. If you are using
another brand you must contact the manufacturer.)
- The fuel line between the tank and the fuel pump is too
restrictive.
- The fuel line between the pump and the regulator is too
restrictive.
- The fuel pump is not getting adequate power supply of
at least 12-volts. Splice a voltmeter into the power wire (red
wire on Mallory fuel pumps) near the pump. With the pump
operating and the engine running at approximately 2000 RPM,
there should be 12-14 Volts at the pump. If not, use larger
wires, a fuel pump relay, or a better charging system.
- The fuel pump is "sucking air". Check the
pickup in the fuel tank and the fittings between the tank and
the fuel pump. If fuel coming out of the pump looks
"milky", there is air entering the system. Air can be
drawn in from a fuel tank pickup that is too high, low fuel
level in the tank and around the fuel fittings (even though fuel
will not be leaking out).
- The fuel pump is "losing prime". Ideally you
want to mount the fuel pump level with the bottom of the fuel
tank, and as close to the tank as possible. Otherwise G-forces
may cause the pump to lose prime. (NOTE: The #1
cause of "burning up" a fuel pump is do to it's losing
it's prime. The fuel running through the pump is actually
keeping it cool.) Having a fuel cell or sumped fuel tank can
cure most prime issues as long as the pump is not mounted too
high.
- There is too much restriction in the return line. With
the engine "off", activate the fuel pump and back the
adjuster screw off. Pressure should now be less than 3 PSI.
|
| Q |
You're running a Nitrous system.
When the Nitrous system is activated, the fuel pressure drops to an
unsafe level. What can you do? |
| A |
- It's best to run two separate fuel systems
with a return style regulator on both systems., or at least in
the Nitrous system. If you're going to use one large pump
(rather than two smaller pumps), you must use two dead-head
style regulators is parallel. However, dead-head regulators are
difficult to adjust correctly in a Nitrous application since the
fuel is not flowing except when the Nitrous is activated.
- Also, dead-head regulators have a slower
recovery time, which can lead to temporary pressure drops. If
you are running only one pump and one regulator (not
recommended), you should use a large return regulator. DO
NOT use two dead-head regulators in series. NEVER
run more than one regulator in a system with a return style
regulator.
|
|