How To Replace A Fuel Tank In A 1990 F-150

Replacing the rear fuel tank on a 1990 F150

You will want the tank mostly empty before dropping the tank, as it weighs about 35 pounds and gas weighs around 6 pounds per gallon. You can siphon it or drive the truck until it is mostly empty. Hit the 4 tank mounting nuts located as shown here with a penetrating spray the night before you do the job. I did mine with wheels on the ground and worked on my back.

You will need the new tank, including a locking ring, new mounting straps and the nylon clips seen here (these are Quick Disconnect #800-015, retaining clip assortment 5/16", 3/8"):

First comes safety - you will want to wear safety glasses when releasing the pressure in the fuel system and when disconnecting the fuel lines at the tank. The pressure is relieved by opening the Schrader valve on the fuel rail. Unscrew the cap, cover it with a rag, and press in the valve with a screwdriver or pointed object.

The fuel tank has 4 hoses and an electrical connector attached to it. At the sending unit, the pressure and return hoses connect, as well as the 4-wire electrical connector. The vent hose is in the center of the tank, and the filler hose connects on the driver’s side. The first step is to remove the filler hose. Inside the fuel door, remove the three screws around the filler orifice. Under the truck loosen the right clamp as seen in this picture, which mounts the filler to the chassis. Slide the clamp off of the mounting ear. Then loosen the left clamp and slide it up the filler body. Now pull the filler away from the filler hose. As shown, there is a nylon pipe inside the filler body that extends inside the filler hose all the way into the tank. By flexing while pulling the filler body you eventually can get it all the way out.

Now you want to break the nuts loose at each end of the mounting straps. Use a box wrench against the frame to hold the bolt head above, and a socket on the nuts below. I used a breaker bar because the nuts were pretty stubborn until all the way off. There are two common ways to lower the tank – with a floor jack and a piece of plywood under the tank, or with motorcycle ratchet straps. I used ratchet straps, as shown in the first photo in this article.

As you drop the tank, the filler hose tends to hold the back up and the front falls faster. This is handy, as the connections at the sending unit are disconnected next. In the below picture, the pressure line is on the left, the return line on the right, and the electrical connection is in the middle and has been disconnected. There are two ears on each side of the connector, and one large locking tab in the center towards the rear of the truck. Carefully pry the tabs to release them, and then pull the connector loose.

The fuel lines have fittings that press on and lock with those new nylon clips. The pressure line has a 3/8” fitting, and uses the black clip. The return line has a 5/16” fitting, and uses the white clip. Pry the clips out by using a small screwdriver under the flat ear, while pressing on the legs to help release them. Remember to use safety glasses, and gently work each hose free of the nipple attached to the sending unit. Some residual gas will leak out.

Detach the vent hose fitting as shown below by prying it upwards. I used two large screwdrivers, one on each side. There is a rubber gasket at this connection that will be needed for the new tank - remove it now or after the tank is out. You now continue lowering the tank - I put several wood 2x6 blocks under it at this point, adding and removing them as necessary to position the tank. Once the tank is resting on blocks, remove the ratchet straps completely.

Now the tank is disconnected, and all you have to do is lower it while sliding the filler hose free of the chassis. Once the tank is out from under the truck, loosen the hose clamp and pry the filler hose off the inlet nipple:

It is recommended that a non-metal chisel/punch be used to remove the locking ring to avoid an explosion. Mine had almost disintegrated, so I loosened it by simply pulling it off. The fuel delivery module is a little tricky to remove, and you need to be careful not to damage the suction screens and float. I could not get it out in one piece. I found that by removing the sending unit (float), attached with three small hex screws, that I could pull the float out first. This made room for the rest of the FDM to come out. Rotate it 90 degrees one way or the other to allow it to come free of the tank.

Installation is simply the reverse of this procedure.

Article written by member.

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