Replacing the Fuel Pump &
Fuel Level Sender
on Your BMW
Wayne R. Dempsey

Difficulty Level: 5
Difficulty scale: Adding air to your tires is level one
Rebuilding a BMW Motor is level ten

[click to enlarge]

     Some common fuel injection problems can be traced back to a faulty or nonoperational fuel pump. If the pump is noisy and loud, or the fuel pressure in the engine compartment is lower than what is needed for proper fuel injection operation, it’s probably time to replace the fuel pump. The fuel pump is not as simple as one might think. The fuel runs through the pump and acts as a coolant and lubricant for the entire assembly. Therefore, if you let the car run out of gas, make sure to you turn off the pump immediately or you might damage the internal components of the pump. There’s nothing worse than having a broken or faulty pump leave you stranded on the side of the road.

     Typical fuel pump problems can sometimes be headed off in advance. If the pump is noisy or making loud clicking noises, chances are that the bearings inside are worn and should be replaced. If the pump continues to make noise even after the ignition is shut off, internal check valves in the pump may be showing signs of failure. The pump could seize up at some time, or the pressure to the fuel injection system could drop. Either way, the car will not perform at its peak. In another form of failure, the pump motor may get stuck and then finally kick in after turning the ignition on and off a couple of times. This could be a sign that you’re living on borrowed time and should replace the pump immediately. Just to be sure, check the electrical connections to the pump before replacement to verify it’s the pump and not an electrical problem.

     Some early E30 cars have a standard fuel pump underneath the car. For these E30 owners replacement of the fuel pump is quite similar to replacement of the fuel filter (see Project 4). This text, however, will focus on the fuel pump and tank sender replacement for 1988-and-later models.

     First, prep the car by removing as much gasoline from the car as possible. Get a long piece of fuel hose and place it down the fuel filler hole. Then hook up a small battery-operated carburetor fuel pump, and pump the gasoline from one car to another. Or, you could buy a gasoline hand pump from most auto parts stores. Either way you go about it, try to remove every drop of gas from the tank.

     Another essential step: Always disconnect the battery before you begin working near the tank. You don’t want any accidental sparks from electrical connections. Some additional warnings:

• Always have a fire extinguisher handy in case an emergency arises.
• Gasoline is highly flammable. When working around fuel and fuel line connections, don’t disconnect any wires or electrical connections that may cause electrical sparks.
• Always remove the gas cap to relieve any pressure in the tank prior to working on the fuel system.
• Do not use a home office or work lamp near fuel or fuel tanks. If you need more light, use a cool fluorescent lamp, and keep it far away from the pump.
• Gasoline vapors are strong, harmful, and toxic. They can make you drowsy and cloud your judgment. Therefore, always work in a well-ventilated area with plenty of fresh air blowing through.
• Always disconnect the battery prior to working on the fuel system. Leave it disconnected for at least 30 minutes before you begin in order to allow any residual electrical charge in components to dissipate.
• Keep plenty of paper towels on hand, and wear rubber gloves to prevent any spilled gasoline from coming in contact with your hands or eyes.
• Be well grounded. Don’t do anything that will create static electricity. Keep all cell phones and pagers a safe distance away.

     Next, remove the back seat from your car. It’s simply clipped in place. Move both the driver and passenger seat all the way forward, crawl in the back of the car, and tug up on the rear seat from the bottom edge. It should pop up with minimal force. BMW designed the car intelligently, so the fuel tank senders and the fuel pump are very easy to get to. (On other makes, you may need to drop the fuel tank to do the replacement.)

     With the back seat removed, you will see sound-deadening material with two flaps, one on the right side and one on the left. The fuel pump is located on the right side of the car, so lift up the right-side flap. You will see a circular cover with some wires emerging from it. Remove this cover and the thin foam seal underneath it. Beneath that, you’ll see the top of the fuel pump.

     Carefully disconnect the two electrical connectors that mate with the pump. Then, while wearing protective gloves, disconnect the fuel lines that feed into the top of the pump. There will be some gas spillage here, so have paper towels on hand. Plug the lines quickly with a bolt or a pen, and use a hose clamp to prevent further leaks.

     The pump is held in place by a big circular disc with the risers on it. BMW makes a special tool to remove and tighten this black plastic ring. However, using a large flathead screwdriver and a small hammer, you can easily tap the plastic ring loose. Carefully remove the ring from the top of the pump.

     Now comes the fun part. Make sure you are fully prepared with a well-ventilated garage, plenty of paper towels, and those trusty rubber gloves. Ready? Pull up on the pump, and the entire assembly should come right out of the tank. There is a big, thick O-ring that seals the pump to the tank. Be careful—it will probably fall to the bottom of the pump. Don’t let it fall into the tank, or you’ll have to somehow fish it out later on. Notice in Photo 2 how brown the bottom filter of the pump looks? Well, the new pump’s screen is completely white.

     You now have an open tank of gas in your back seat. Needless to say, you don’t want to leave the car like this for too long. However, you also don’t want to work too quickly, as you don’t want to make any big mistakes.

     You can reuse the old sealing O-ring, but I usually opt for a new one. If you do use the old one and it doesn’t seal well, you will be plagued with a fuel smell in the interior of your car from this point on.

     Insertion of the pump into the tank is the reverse of removal. Make sure the big O-ring is properly sealed around the outside of the pump and that it will seal with the opening of the tank. The new pump needs to sit snuggly on the top of the tank. To safely seal it, spin on the large circular ring, and tap it with a hammer or screwdriver to tighten it. For this project I tightened mine about as far as I could go without feeling that I’d break the ring. Next, reconnect the fuel hoses using new hose clamps.

     Once all fumes have subsided, plug in the new fuel pump and reconnect the battery. Then crank the car over and see if it starts. If the car starts and runs for any length of time, the pump is working fine. Replace the top cover and foam seal. Finally, reinstall the back seat by pushing it down into its home position.

     Replacing the fuel tank level sending unit follows a very similar process. On late-model E30 and E36 BMWs, there are two level sending units—one on the left side, and one on the right side that is integrated into the fuel pump. The procedure for the replacement of the fuel sender on the left side is identical to the procedure for replacement of the fuel pump on the right side.

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