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Using my 1993 Mustang LX as the demonstration car, this article will detail the steps necessary to replace the intank fuel pump in a fuel injected Mustang with an aftermarket higher flow rate (255 liter per hour) performance fuel pump. To install this fuel pump, modifications to the factory wiring on the fuel pump tree will be necessary so that a new electrical plug which puts the wiring to a single connector can be installed. You'll see what I mean at step 2L of this article. For those installing a direct replacement fuel pump, my article notes the steps necessary to complete this installation as well.
All of these steps will apply to all engines but some extra pictures will show details specific to the 1994/95 5.0L engine and the 1994-2004 3.8L v6 mustang.

This job should take about 2 hours total from start to finish.

Required tools:

Jack and jackstands (or substitute drive on ramps for the jackstands)
1/4" drive ratchet and extensions
1/4" drive 8mm socket, 10mm socket, 3/16" socket, 1/4" socket
3/8" or 1/2" drive ratchets and long extensions
3/8" or 1/2" drive 13mm deepwell socket
hook tool if available
flat tip screwdriver
brushes or cloths for cleaning and wiping (optional)
brake cleaner (optional)
soldering iron with solder
heatshrink tubing sized for 10ga wiring
wire stripper/cutter


Step 1 - Empty the fuel tank

a. Drive the car until the fuel tank gauge looks like this:

Step 2 - Relieve the fuel pressure from the fuel system

a. Disconnect the inertia switch plug from the switch. This plug is located behind the drivers side taillight. You will have to remove the interior panel covering up the back of the taillight to access the plug for disconnection.

b. After disconnecting the switch try to start the car. If the engine does start, it should stall out almost immediately and not start up again. This is how you will know that the fuel system pressure has been relieved.

Step 3 - Raising the car for fuel tank removal

a. Using the jack, raise the car by placing the jack under the center of the rearend "pumpkin" high enough for clear access to the fuel tank.
Place the jackstands beneath the rear subframe area or place drive on ramps beneath the rear tires. Lower the jack so that the car rests on the drive on ramps or jackstands

Step 2 - Lower the fuel tank

a. Unplug the fuel pump wiring harness from the chassis harness

b. Locate the fuel tank straps and their 13mm bolts ------

Drivers side strap:

Drivers side strap with 13mm socket and extension for removal:

passenger side bolt:

c. With the jack supporting the fuel tank, remove the 13mm bolts and swing the fuel tank straps out of the way of the tank

d. Lower the tank about halfway down, the drivers side of the tank wil naturally lower itself a little further because the fuel inside will flow that way and the filler neck is holding the passenger side of the tank from lowering.

e. There is a small bracket going around the filler neck. The bracket is bolted to the fuel tank lip with an 8mm or 10mm bolt. Remove the bolt, move the bracket back away from the fuel tank lip.
f. While pushing the fuel tank towards the drivers side, pull the filler neck until it is free from the fuel tank

g. This is the fuel pump tree with the fuel lines still connected at the top of the fuel tank when the tank is lowered:

h. Using the fuel line quick disconnect tools, choose the small blue tool from the package ------

i. -------- and disconnect the fuel lines from their connections at the top of the fuel pump tree. The fuel line at the right in the first photo uses a duckbill clip that is removed by spreading the legs and pushing the plastic clip up through and out of the black fuel line fitting.

86-93 model year fuel lines:

1994 and up 5.0L and 3.8L fuel lines, some 4.6L fuel lines:

j. Locate the Purge vent where it is plugged into the top of the tank

k. Remove the purge vent

l. Unplug the red electrical connector from the top of the fuel pump tree.

Step 3 - Removal and disassembly of the fuel pump tree

a. Using a flat tip screw driver and a hammer, tap the raised area of the retainer ring so that the ring rotates counterclockwise.

b. Ring in position for removal:

c. Lift the ring up and over the fuel line connections and away from the fuel pump tree:

d. Using brake parts cleaner, a cloth and brushes, clean up the area at the top of the fuel pump tree before removing fuel pump tree assembly:

f. Looking inside the tank, you can see the fuel pump strainer that will present a bit of a challenge while attempting to pull the fuel pump assembly out of the gas tank. The fuel pump assembly needs to be rotated as you are lifting the assembly up at an angle to facilitate removal.

Inside the tank:

Lifting the assembly from the tank:

g. Once the fuel pump tree is lifted high enough from the tank to where you can see the pump strainer, use a pick tool to grab the strainer. Once you have control of the strainer, detach the fuel pump tree from the strainer by pulling it straight off the strainer. CAUTION: Be very careful of the skinny rubber gasket that sits on top of the opening of the fuel tank, you don't want this gasket falling into the tank.

h. Fold the strainer to make it easier to remove from the fuel tank:

The metal ring and the black rubber gasket used to seal the fuel pump assembly to the fuel tank:

Fuel pump assembly removed the from fuel tank:

i. Using the 1/4" drive ratchet with 3/16" socket, remove four screws holding the lower bracket to the upper bracket on the fuel pump assembly tree:

j. With the four screws removed, separate the lower bracket from the upper bracket. Pay careful attention to a small black rubber gasket that is placed between the very bottom of the fuel pump and where the fuel pump seats into the lower bracket. This gasket will be reused with the new fuel pump.

k. Using a 1/4" socket, loosen the clamp holding the rubber hose to the fuel pump. Separate the hose from the fuel pump.

l. In the next photo, note the two spade type electrical connections to the fuel pump. Pull them off their connections to the fuel pump.

At this point if you are replacing your fuel pump with a Ford factory pump or Autozone/NAPA/Advance Auto Parts replacement pump you can reconnect the wiring to the new fuel pump and then skip down to step "r" to continue installation.

If you are installing an aftermarket performance fuel pump with a higher flow rate such as those from Walbro, continue with step "m".

m. Matching up the wiring for the plug for the new fuel pump, line up the wiring for the old harness on the fuel pump tree.

n. Using wire cutters or a similar tool, cut the wiring from the old harness. Using a wire stripper, remove the insulation on the old wiring and new wiring to expose at least 1/4" to 3/8" of copper.

o. Cut two sections of wiring shrink wrap about 1.5" long each. Install them on the old wiring, sliding them up to near the top of the fuel pump tree. Fold over each of the four exposed copper wiring sections to look like a hook. Hook the red wires together and then hook the black wires together. Press the ends of the hooks down so that the wiring ends are secured.

p. Using the soldering iron, apply heat to the exposed copper wiring. Once the wiring is hot enough, apply the solder which will melt into the wiring to make a secure connection that will allow maximum conductivity of the electrical current needed to power the fuel pump.

q. Next, slide the shrinkwrap down so that it covers up the exposed/soldered copper wiring. Using a lighter or similar flame producing device, heat the shrinkwrap so that it forms over the exposed wiring and becomes a coating. This will protect the new soldered connection from corrosion.

r. Align the new fuel pump so that the black rubber fuel hose can be installed over the outlet nipple of the new pump.
s. Tighten the 1/4" screw down clamp onto the hose.
t. Using the black rubber gasket that was removed from the old fuel pump when the lower bracket was removed, install the gasket over the bottom of the new fuel pump.
u. Install the lower bracket over the bottom of the new fuel pump and align it with the upper bracket of the fuel pump tree.
v. Route the wiring with the plug so that you can plug it into the new fuel pump.
w. Install and tighten the four 3/16" screws with the 1/4" drive socket and ratchet. The next photo shows the new fuel pump assembly completed.

x. Next install the new fuel pump strainer to the bottom of the fuel pump. It presses very tightly into place. The small metal alignment tab on the bottom of the fuel pump lower bracket will sit to the side of the new strainer. The long side of the new strainer will point to the front of the fuel tank when the fuel pump assembly is installed into the tank.

y. In this next photo, align the rubber gasket around the opening of the fuel tank prior to lowering the fuel pump assembly into the tank.

z. Lowering the fuel pump assembly into the tank, the long end of the strainer needs to be put into the fuel tank first.
Position the fuel pump assembly so that the short end of the strainer can be easily slid into the tank next.
Looking inside the tank from the filler neck hole, lower the fuel pump assembly and rotate it so that the strainer aligns with the boxed opening in the lower half of the fuel tank. The strainer will be lowered into the lowest part of the tank this way.

Step 4 - New fuel pump assembly installed into the tank:

Once the assembly is seated at the top of the fuel tank opening........

a. ...........Place the metal ring over the fuel line connections and seat it so that the fuel tank alignment tabs are are lined up with the slots in the ring. Use a flat tip screwdriver and a hammer to tap the ring clockwise until the rings vertical tabs stop against the tabs on the fuel tank.

b. Plug in the red electrical connector to the top of the fuel pump assembly.

c. Reinstall the purge valve connection to the fuel tank.

d. Side Note: While the fuel tank was removed from the car I pulled the tank from the plastic tank tray for detailing. I washed the plastic tray and then sprayed it in flat black paint to bring back the new look. I also removed the fuel tank straps from the car (held in by roll pins that are easily pushed out of the bracket openings), sanded them down and sprayed them in an aluminum silver paint. These are the results:

e. Obviously place the fuel tank back into the tray and slide the fuel tank back underneath the car. Place the fuel tank onto the jack and raise it up into place so that the fuel lines can be reconnected. They slide and then snap into place for a secure connection. The Left side fuel line is a quick connect fit and the line on the right uses a duckbill connector just like the fuel filter ends. Slide the legs of the duckbill connector into the openings on the black fitting with the "arrow" top of the duckbill facing away from the end of the fuel line connector that its going into.

f. Raise the fuel tank high enough to align the fuel filler neck with the tank opening on the passenger side. Slide the filler neck into the tank opening while sliding the tank towards the passenger side of the car. Continue to raise the fuel tank until the straps clear the bottom of the fuel tank and are able to align with their bolt holes with the chassis bolt holes.

g. Install the two 13mm bolts to secure the fuel tank straps to the chassis.

h. Install the 8mm bolt that secures the filler neck bracket to the fuel tank lip.

i. Plug in the fuel tank wiring harness to the chassis harness at the very back of the fuel tank. At this point if you are not installing a new fuel filter (although it is highly recommended to install a new fuel filter when you install a brand new fuel pump) you can lower the car. Place the jack beneath the rearend "pumpkin", slightly raise the car to slide the jackstands or ramps from underneath the car and lower the jack and the car to the ground.

j. Inside the trunk or hatchback opening, behind the drivers side taillight, reconnect the plug to the inertia switch. Push in the red button if it popped up.

k. Reconnect the battery terminals. Inside the car, put the key into the ignition and cycle the ignition switch several times slowly between "off" and "ignition on" (not start or run) to prime the new fuel pump. This will power the fuel pump so that fuel pressure builds. After 3 or four cycles, the engine should start and the installation is complete!!
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