Replacing a Fuel Sending Unit in a 1990 Volvo 740

This post will cover the experiences I had while replacing the Fuel sending unit in our 1990 Volvo 740 Turbo Wagon. We knew it needed to be replaced because the fuel gauge wasn't registering a fuel level (The Sending unit contains a float that can get stuck or deteriorate over time).

Tools Needed:

• Assorted Metric Sockets
• Pliers
• Something to cut rubber hoses
• Phillips Screwdriver
• Standard Screwdriver

 Parts Needed:

1990 Volvo 740 Turbo Fuel Sending Unit

 The Fuel Sending Unit is located in the fuel tank. Volvo was nice enough to provide a access panel located directly above the Bunk Nut that holds the sending unit in the tank.

Procedure:

• Disconnect battery negative.
• You will need to remove the trim on the drivers side rear cargo area.

• Fold the rear seats down

• Lift the drop panel that folds down when you flip the seats down.

• Remove the 3 bolts that hold it in place.

• You will now see an access panel that is either black or painted to match on the drivers side rear cargo area floor. It is held in place with 4 bolts.

• After removing the access cover, note that the tank top is fairly well coated with road grime, but not rusty.

• Following the pump outlet from the compression fitting at lower left the flare fitting junction with the steel feed line can be seen near upper right of opening.

• Make more access room by first disconnecting filler vent line. Be careful you do not damage the electrical wires.

• Then disconnect filler hose.

• To remove the Volvo quick disconnect fitting on the fuel outlet line (the 90-degree fitting below), place your first two fingers on the back of the cylindrical sleeve on the metal tube, your thumb on the 90 degree fitting, press them together, and pull the fitting off. You may need a little penetrating oil to free up the inner o-rings from rust on the tube.

• The fuel return line has a steel spring clamp. To remove this intact, try adjustable water pump pliers or long, angled needle nose pliers.

• Tap the plastic lock ring loose. The threads are huge, so about two turns and it is off. Don't use the screwdriver shown: use a piece of wood instead to avoid cracking it.

• Separating the sender cap from the soft rubber seal underneath; the lip is only about 1/8 thick. In the event you have a difficult time pulling the sending unit from the tank because it is stuck, use a flat-blade screwdriver with a wide tip (3/8") and a rubber mallet. Don't pull on the tubes that go through the sender's top. Tap gently against the sender unit's top lip. Using steel on (old) plastic requires that you go slowly. The send unit will back out.

• Disconnect the sender wiring harness from the connector in the left side wheel well, then cut the zip ties holding the wire to the fill tube. Fish this harness out through the grommet hole near the fuel sender unit. There may be a wiring harness holder way up on the left under the deck: using a screwdriver, release the lock and pull the wires free.
• Now the unit can be withdrawn from the tank. Use a flashlight to see what is going on inside. The send unit's "barrel" - positioned just forward of the fuel tank's rear wall - points straight down (towards the tank's floor). In front of the send unit, there is a white plastic "baffle". It prevents fuel "slosh" (to keep the fuel gauge needle as stable as possible during turns, or sharp stops, etc.). The fuel send unit has to be maneuvered around this baffle. By turning the unit counter-clockwise (to your left, as you face the front of the car), to the 10 o'clock position, you move the barrel around the corner of the fuel tank baffle. At the same time as you move it, pull upwards and - as much as possible - tilt the top of the send unit towards the back of the car. This has the effect of lifting the end of the barrel so that it above the baffle. Once the barrel is clear of the baffle, you should be able to lift the unit out of the tank.

Installing Into the Tank: Take a good look at the yellowish anti-slosh pan on the bottom of the tank. See the high side and rear wall plates? You'll need to maneuver the assembly around them. Leaving the rubber seal off, insert the assembly in through the hole in the tank so that the bend in it points more-or-less at 3 o'clock. Push the assembly in some more while rotating it counterclockwise. When installed, the fuel sending unit is located next to the back wall of the fuel tank. The fuel pump intake (the end with the filter "sock") needs to point straight down (towards the tank bottom) and to be parallel to the tank's rear wall. The reason: when going uphill with little fuel, the fuel will pool in back of the tank towards the vehicle's rear, where the pump can draw from it. To get the fuel send unit seated, it is necessary to swing it to your right (as you face the front of the car) so the end of the "barrel" can clear the in-tank baffles. Then, the top of the send unit needs to be lifted slightly and rotated forward towards the front of the car. This allows the end of the barrel to point straight down. You can then lower the unit into place. As you insert the unit into the tank, keep the string slightly taut. You will have to insert it first uncompressed, then as you maneuver the unit top past the lip into the tank, you can pull up on the string to compress the unit so the bottom of the sender clears the left side baffle and the filter and pump clear the front baffle walls.

Seal installation: Since the in-tank side of the seal has two concentric lips, it's next to impossible to get it to seat while the seal is on the sender/pump assembly cover. Instead, you have to seat the seal in the opening and push the assembly through. Pull the sender assembly out so that the cover with its rim clears the tank. Apply some Vaseline on the inside and outside of the seal and onto the seal seating surfaces (cover and tank rim). All four surfaces (inside/outside of seal and mating plastic surfaces of tank and cover) must be slippery. Don't overdo it -- smear it thinly all over the seal and mating surfaces. Stretch the seal a tad and pull it over the sender assembly cover. Push the seal about halfway into the rim in the tank. With a rotating rocking motion (rock the sender in the seal slightly), slowly push the sender assembly's cover into the seal, and use it at the same time to fully seat the seal in the tank. After it's fully seated, pull the assembly out about 1/8". Feel the gap between the tank rim and the sender assy cover - make sure that the slight flange on the seal is present all around the cover. If you've pushed the seal improperly so that the flange made its way into the tank, pull the assembly out enough to be able to repeat pushing the seal halfway into the tank and following. With slight rocking, push the assembly back fully into the seal.

Replace the tank lock nut: Screw this down until it contacts the face of the sender top, then about 1/4 turn more to compress the gasket. If your locking ring did not come encircled with a large hose clamp (most 940s did: the clamp reinforces the locking ring), get a clamp. The hose clamp should initially be partly tightened and then in stages as the lock collar is being threaded on, ending up only just snug and not overtightened. The collar is only supposed to be hand-tightened, but when working through the access hatch it may be more difficult to accomplish adequate torque so you might LIGHTLY tap it counterclockwise using a piece of wood on the outer serrations and a mallet. The most important thing in getting a good seal is to have the sender face plate absolutely flush on top of the rubber gasket before installing the lock collar.

NOTE: This is a tight space to work in and will require patience. Also the old unit has bent inlet and outlets for the fuel lines. The new unit has straight inlet  and outlets. This required me to purchase new fuel grade lines from NAPA auto parts.