Fuel pumps can be a common replacement item on any car, including E39 BMWs. Symptoms of a failing fuel pump can include hesitation and loss of power under wide open throttle, difficulty starting or unexpected stalling. If you are unable to start a car and suspect fuel delivery, you can reach underneath the car in front of the rear wheels on the right hand side of the car, and thump the bottom of the tank with a piece of 2x4 timber or similar. If the fuel pump is faulty it may jolt it into life and you have confirmation.
However, the same symptoms (loss of power, stalling, difficulty starting) can be other symptoms such as failing ignition coils or leads or other ignition related items such as engine sensors. (see DIY for E39 Camshaft Position Sensor) So care should be taken to correctly diagnose by elimination before diving directly into replacing the pump.
The fuel pump in E39 BMWs is located inside the tank (as is common with most cars these days) and runs ‘wet’ with fuel. Replacing the pump requires opening the tank which brings with it the possibility of fire and the definite occurrence of fumes from the fuel. If you are going to undertake this task be sure to have a fire extinguisher to hand and plan to do it in a well ventilated area. I’m pretty sure the BMW manual says to drain the tank before changing, but that is not practical for most people so it usually gets done ‘wet’. You probably won’t get a choice of how much fuel there is in the tank when it fails, but it’s definitely better done with the fuel level low.
Tools and Materials
- Flathead screwdriver
- Philips head screwdriver
- Small flashlight (no need to use a kerosene lantern here!)
- New Fuel Pump
Optional (if required to separate pump from sender unit and cap to remove):
- Sidecutters and Zip ties
- New hose clamps
BMW E39 Fuel Pump Replacement Procedure
Disconnect the battery by opening the luggage compartment and removing the negative (brown) lead from the battery. I like to put a rag or similar on top of the battery so the cable can’t fall back into place if the car moves.
Start by removing the rear seat. There are no fasteners holding in the seat – it just pops up and out. Grab the seat firmly at the front and lift up and out. It might take some force if you haven’t removed it before. If you have a touring you’ll need to work the seatbelt buckles through the locating holes.
Find the fuel tank access hole underneath the black rubber/plastic sound insulation. It is a round cutline in the sound insulation – carefully peel this back to reveal the top of the access plate.
Remove the access plate by removing the screws holding it in. Remove the wiring harness connector as the access plate is removed.
Underneath the access plate is the access hole for the tank. The fuel hose will be visible with a small clamp – loosen the clamp by squeezing and remove the fuel line. It’s likely some fuel will leak so have a rag ready to soak up any spills. I used a screwdriver to plug the hose to prevent any further leaks from the hose.
The cap is held in by a threaded ring. Use the flathead screwdriver to provide lateral force on the tabs inside the ring and screw it out. It should only take moderate force as it is not torqued to a high level. If it is stuck get a helper to tap another screwdriver on the opposite side to provide balanced torque.
Once the screw ring is removed the cap will lift out. Be very careful when lifting – underneath the cap is the fuel tank sender unit, and this is suspended on delicate wires. You will have to work the mechanism out of the hole carefully as it will not lift directly up and out.
Looking into the hole with the cap and fuel sender mechanism partially removed, you’ll see the pump sitting vertically in a plastic ‘swirl pot’. At this point you can reach down with your hand and release the black plastic tabs that hold the pump in place by squeezing them together. There are no screws holding the pump in place as it is a ‘clip fit’. Gloves might protect your hands but be aware of depositing anything in the tank except for fuel. If the fuel level is low (as in this picture) you won’t have to submerse your hands, but if it’s high you’ll get them wet.
Once the pump is released you can lift the entire mechanism out – cap, sender, hose and pump all attached. Lay this out on some paper to absorb any fuel. Place something over the top of the hole in the tank to prevent further vapor venting from the tank.
Release the wiring harness connector by pulling the steel retainer out, which will release the connector. Release the clamp holding on the fuel pipe, and then remove the pump from the plastic retainer.
At this point you can refit the new pump by fitting it into the plastic container, and reclamp the fuel pipe onto the pump. There is a locating lug on the bottom of the pump that aligns with an offset hole on the bottom of the holder – this should be pushed in all the way and aligned correctly. Refit the wiring harness making sure it is all oriented in the same way.
Now you’re ready to refit the pump/sender assembly back into the car. The procedure is ‘reverse of removal’. This is a tricky operation as everything has to be threaded back into the hole in the top of the tank. First ensure that the pump and housing clicks back into the swirl pot holder. Then feed the remaining wiring and hose back in through the hole, but offer up the sender unit through the hole, rotating to get it all to fit. It is hard to describe, but take your time, don’t force anything and be careful and it should go back in fine. If you make a mess of it and bend something it’s likely your fuel gauge will start being inaccurate. So be careful!
Seat the cap back in place making sure the rubber seal is seated properly. Screw the retaining clip back in place and tap home with the screwdriver, working around the rim. No need to overtorque, just make sure it is on firmly. Reattach the wiring harness and fuel pipe, making sure the clamp is done up firmly. The OEM clamps can be difficult to retighten, so consider new hose clamps. You don’t want this pipe coming undone and leaking fuel underneath the car. If you have spilt any fuel, wipe it up so you can check for leaks later.
Once it is all tightened back up, fit the access cover plate and replace the sound insulation on top. Reconnect the battery. At this point you can try the car and see if it starts OK. If not, you’ll need to go back and check everything for correct connections. It may take a second or two for the fuel pump to prime the lines with fuel before starting. If you have to re-open the tank remember to disconnect the battery first.
If everything is working OK put the back seat back in and go for a test drive! When returning from the test drive, do a quick visual inspection under the car to smell for fuel and visible leaks. There should be no smell and no leaks.
The most difficult part of this job is threading the pump, lines and sender in and out of the access hole in the tank. This requires a bit of juggling with both hands to feed all the parts in (or out). It’s very important not to bend the mechanism which holds the sender and not to twist or break any wires.