Fuel Pump Installation
MN12 Performance Inc. in-tank electric fuel pumps are rated at 190lph
([email protected] 54psi), 255lph ([email protected] 58psi) and 255lph (HP)([email protected] 67psi). The
lph pump kit and is an excellent replacement for stock engines and
engines with bolt-on parts. The 255
lph pump kit is excellent for supercharged cars. The 255
High Pressure pump is rated for higher fuel pressure applications.
Each chart shows fuel pressure in PSI and Gallons Per Hour (GPH) of fuel
flow. Typically, at wide open throttle, full power, an engine requires
0.5 lbs. of fuel per horsepower every hour. A gallon of gasoline weighs
approximately 6 lbs. Therefore an engine rated at 350 horsepower will require
about 175 pounds (29 gallons) of fuel every hour. (350HP x .5lbs = 175
lbs of fuel, 175 lbs/6 lbs = 29 gallons per hour) If you were looking to
support a 406hp 3.8L SC engine your pump would need to flow at least 33.83gph
of fuel. Keep in mind as fuel pressure increases the GPH decreases. Stock
fuel pressure is around 32psi - 34psi with the vacuum connected to the
fuel pressure regulator. Normally aspirated engines will see about 45psi
max of fuel pressure. Supercharged fuel pressure can see about 1 psi above
45psi for every lb of boost the engines sees. So a Thunderbird SC with
33lbs of fuel pressure at idle with a 15psi supercharger setup will see
upto 58psi of fuel pressure. As the charts show the individual pump flow
data you need to know before selecting the proper size fuel pump for your
Fuel Pump Diagnosis:
If your fuel pump stops working (no noise, no line pressure), the first
thing that should be checked is the pump's voltage supply and electrical
connections. An open relay, blown fuse or loose wire may be all that's
preventing the pump from working. Low battery voltage can also reduce the
pump's ability to generate pressure by reducing the speed of the pump motor.
Replacement would also be required if the pump's check valve has failed
(inability to hold residual pressure in the system after the ignition is
turned off). The plastic baffle that connects between the pump and fuel
pump hard line is another common failure resulting in fuel rail line pressure
Drive the car until the "Check Gauge" light comes on
signaling that you have about 2 gallons left in the tank (each gallon weights
6lbs). Disconnect battery ground cable. Then pump the rest of the fuel
out into a suitable container.
Next, Lift the vehicle on a hoist, using jack stands is NOT recommended.
Keep ALL lights and electrical power away from the car while you
are working with the gas tank.
Note: The nylon fuel tube connections
are on top of the fuel tank and are inaccessible.
They must be disconnected with the fuel tank
partially removed from the vehicle.
Next, remove the rear section (cat-back) of the exhaust system
and heat shield.
Remove the four 13mm bolts that hold the fuel tank in the car.
Then tilt the fuel tank down and disconnect fuel tank to filler pipe
hose and vent hoses connecting the fuel tank filler pipe to fuel tank.
Disconnect the fuel lines, disconnect the rear fuel supply return, vapor
tubes, and electrical connector from the fuel pump then remove remove from
car. Mark the location and reuse the heat shields. (see
Pull locking tabs. Don't worry about breaking them as new ones are included
in the Fuel Pump Kit. One Black and one White.
Pull hose off vent.
Using flat blade screwdriver or 5/16" socket loosen the clamps.
Then pull hoses off.
Remove fuel tank from car and move it into a clear open area. Using
Parts cleaner or Brake cleaner wash dirt away from pump area. This maybe
a good time to wash the tank and check for any problems. Note: Be sure
to cover the fuel filler and vent openings so water does not get in the
Remove the locking ring that secures the fuel pump.
Look at the filter to float clearance. Make sure the new filter has proper
clearance from the float.
Then slightly bend the pump bracket to allow enough room to remove the
Once the filter is removed there is a retaining ring that holds the
pump in the place. Using a small flat blade screw driver evenly pry the
retaining clip. Note: Not all fuel pump assemblies have this retaining
Next, Disconnect the electrical terminals from the pump by depressing
the tab on the locking terminals.
Slide the Pump Baffle up to allow clearance so the pump can be removed.
Pull black rubber insulator off fuel pump. It will be reused on new
Strip the shrink tubing from the positive wiring at the connector.
Insert the RED Positive wire with quick connect terminal into the new
connector. Cut the Negative wire at about 1/2 way and using the supplied
connector crimp the two wires together then heat shrink the tubing to seal
Then insert the orange retaining clip back into the fuel pump connector.
Cut the 5/16" high pressure fuel hose down to 2" and insert one
end to the fuel pump and the other to the pickup hard line. Rotate the
pump until the two line up. This hose replaces the plastic baffle and is
necessary to get the most out of your new fuel pump.
Reuse the black rubber insulator. Slide over new pump.
Clamp the hose to the pump with the supplied stainless steel clamp.
Install the pump back into the bracket. Installing the hose over the
hard line and installing the clamp. Connect the power to the pump. Reinstall
retaining clip to secure pump to bracket. Some models do not have this
retaining clip. Finally install the filter. Align the filter before pushing
it on the pump.
Install the pump assembly back into the fuel tank using the new gasket.
Note: If the gasket is too small try stretching the rubber by pulling in
sections around the entire gasket until the gasket fits correctly. (see
picture below) Apply a thin layer of some wheel bearing grease
to the gasket before installation. This will help the gasket seat and not
Gasket must sit inside groove for proper seal.
The tank uses these alignment tabs.
If your sending unit retaining ring is damaged or rusted you can get
a replacement. Motormite products www.rbinc.com
sells replacement Sending Unit Retainer Kits as part number 55811.
The gasket is included with the kit.
With the gasket in place hand tighten the locking ring clockwise then
tap it home with a screw driver and hammer, make sure the retaining ring
is fully seated. Reinstall the fuel tank back into the car. Reconnect the
hoses and electrical connector then tighten the support strap bolts that
hold the tank in place. Install new fuel filter. Located on passengers
side subframe. Special tool is required to disconnect the fuel filter retaining
clips. Available at most autoparts stores. Lower the vehicle and reconnect
the negative terminal. Key the ignition and verify fuel pressure at the
fuel rail. Also check for any signs of fuel leaks at the pump or filter.
Start the car and recheck fuel pressure.
MN12 Performance Inc.
Fairfax, VA 22033