Replacing High-Pressure Fuel Pumps: Step-By-Step Guide For Diy Mechanics

Replacing a high-pressure fuel pump is a complex process that requires careful attention to safety and a range of tools. The procedure varies depending on the car model, but generally, it involves removing engine bay covers, disconnecting fuel lines, and carefully removing and replacing the pump. The pump's location and the specific tools required differ depending on the car's year, make, and model. For example, the process for a BMW 3-Series involves removing the intake manifold and radiator fan, while a Porsche Cayenne Turbo requires removing the belly pans and plastic engine cover. Safety precautions are critical, as petrol is highly flammable, and spills or leaks can occur during the process.

Expose the fuel pump

To expose the fuel pump, you will need to remove several plastic covers from the engine bay. First, grip the front of the engine cover and pull it up to pop it off the front locating pins. Then, grab it by the right side and pull it up to pop it off the last pin. For pre-2013 engines, there are also two vacuum lines on the passenger side of the cover that need to be disconnected.

Next, remove the foam noise-reduction pad underneath the plastic engine cover. Then, move to the engine cowl and use a 10mm socket to rotate the fasteners at the back of the cowl by a quarter turn. After that, remove the plastic rivets securing the cowl near the fenders.

Removing those forward cowl pieces exposes the strut brace. To access it, remove the two plugs from the rear cowl's centre. Then, pull the rubber strut covers off and remove the bolts with an E18 socket. You will need to remove a plastic rivet to remove each strut cover.

Finally, remove the cover that sits below the brace using a 10mm socket to take out its seven bolts.

If you are working on a Porsche Cayenne, you may also want to remove the belly pans and plastic under trays so that dropped tools fall to the floor instead of becoming trapped in the pan. This will also allow you to visualise the pump from under the car to inspect for fuel leaks and look at things from another angle.

Disconnect the fuel system

Disconnecting the fuel system is a critical step when changing a high-pressure fuel pump. Here is a detailed guide on how to do this safely and effectively:

Step 1: Cut Power to the Fuel Pumps

Before you begin, ensure that you cut the power to the fuel pumps to prevent them from accidentally turning on while the fuel system is open. You can do this by removing the fuel pump control unit fuse in the engine bay fuse box. Alternatively, you may choose to disconnect the battery or remove a relay. This step is crucial for safety.

Step 2: Depressurise the Fuel System

It is recommended to release some of the pressure and fuel from the system before opening it up. If your car has been sitting for several hours, the pressure should naturally bleed off over time. However, if you want to accelerate this process, you can pull the fuse as mentioned above and then attempt to start the car. It may run for a few seconds before dying, which will help relieve the residual pressure and fuel.

Step 3: Loosen the Low-Pressure Fuel Line

Using the appropriate size wrench, typically 18mm or 19mm, loosen the low-pressure fuel line from the pump. Have a cloth or container ready to catch any spilling fuel. Make sure to note the orientation of the hose and any reference marks for reassembly.

Step 4: Remove the Crash Panel

At the back of the pump, there is usually a black metal crash panel or cover that needs to be removed. It is typically attached with three bolts, which you can loosen with a wrench and then remove by hand. This step may require working in a tight space.

Step 5: Disconnect the High-Pressure Line

Now, focus on the high-pressure line that runs from the pump to the fuel rail. Again, have a cloth or container underneath to catch any spilling fuel. Be careful not to bend this line. Loosen and disconnect the line at both the pump and the fuel rail.

Step 6: Remove Fuel Line Bracket

To completely remove the fuel lines, you will also need to disconnect the bracket holding them in place. Remove the bolts securing the bracket with the appropriate size socket and then push it back and out of the way.

Step 7: Disconnect the Low-Pressure Line and Electrical Connection

With the high-pressure line removed, you can now disconnect the low-pressure line that runs below it. Use a wrench of the correct size, typically 17mm. Also, don't forget to unplug the pump's electrical connection. At this point, the fuel system should be successfully disconnected from the pump.

It is important to note that working with fuel systems can be dangerous, and you should always prioritise your safety. Ensure proper ventilation, have a fire extinguisher nearby, and avoid opening the car doors while the fuel lines are disconnected to prevent accidental activation of the fuel system.

Replace the high-pressure fuel pump

Step 1: Expose the fuel pump

Remove the engine cover by pulling it up from the front locating pins. For pre-2013 engines, disconnect the two vacuum lines on the passenger side of the cover. Remove the foam noise-reduction pad underneath. Next, remove the engine cowl by rotating the fasteners at the back with a 10mm socket and removing the plastic rivets. This will expose the strut brace. Remove the plugs from the rear cowl's centre and pull out the rubber strut covers. Remove the brace's mounting bolts with an E18 socket and pull the brace out. Now, remove the cover below the brace using a 10mm socket.

Step 2: Disconnect the fuel system

Use a 17mm wrench to disconnect the high-pressure feed line from the pump to the rail. Have some rags handy as there will be fuel in these lines. Follow the line back to the rail and disconnect it there as well. Do not open the car doors from this point until you have reconnected the fuel lines, as it will prime the fuel system and spray high-pressure fuel all over the engine bay. Disconnect the bracket holding the fuel hardline with an E6 socket and push it back. Remove the high-pressure line from the engine and disconnect the low-pressure line with a 17mm wrench. Finally, unplug the pump's electrical connection.

Step 3: Replace the high-pressure fuel pump

Remove the fuel pump's mounting bolts with a T30 socket, going back and forth to prevent the pump from getting pushed out crooked by the cam follower. Remove the old gasket with a pick and the old cam follower with a magnet.

If your BMW model is an early N20/26 engine, the new pump will have a different fuel quantity control valve and will use a different plug and connector for the wiring harness. You will need to clip the plug on your old harness and solder on the new one. Compare the fuel pumps before clipping anything. Clip the old plug off the harness and crimp on the new connector. Cut off the excess harness and attach the new plug to the engine harness. Slide some shrink tubing onto each wire, then connect the white wire with a green stripe to the red wire, and the white wire to the white wire. Use a heat gun to shrink the tubing onto the connections.

Now, install the new cam follower. Dip the follower in oil or apply assembly lube before setting it into the cylinder head. The follower will only fit one way, with the notch facing down. Press the new fuel pump gasket into place.

Slide the bracket from the old pump onto the new one and install them onto the engine. Hold the fuel pump in place while threading in both mounting bolts by hand. Use a T30 socket to tighten the bolts.

Reconnect the fuel lines to the pump. Thread on the low-pressure line first, then bring the new high-pressure line onto the engine and connect it to the fuel rail and the fuel pump. Use a 17mm wrench to tighten all the fuel line fittings. Use a T30 socket to torque the fuel pump bolts to 12Nm. Refit the bracket over the fuel lines and tighten its bolts with an E6 socket.

Finally, plug the new wiring harness connector into the new fuel pump.

Step 4: Refit the engine bay plastics

Refit the noise insulation pad to the valve cover. Slide it under the tabs at the back of the engine cover and press the rest into place. Refit the lower cowl piece by threading in the fasteners by hand and tightening them with a 10mm socket. Install the strut tower brace by loosely threading in the bolts by hand, then use an E18 socket to drive them in and torque to 56Nm, plus 90° of rotation. Reinstall the upper cowl pieces by sliding them into place and using a 10mm socket to turn the locks. Refit the plastic rivets on their outer edges.

Now, refit the hood seal to the strut brace and run the cable through it. Refit the rubber strut covers and secure them with their plastic rivets. Finally, refit the engine cover and reconnect the vacuum lines if necessary.

Tips and Warnings

• If you need to open the car door with the fuel lines disconnected, disconnect the battery first.
• When soldering the new wiring harness, make sure to cut off the excess from the old harness before attaching the new one.
• When tightening the fuel line fittings, torque to 13Nm or 9.5 ft-lbs.
• When torquing the strut brace bolts, torque to 56Nm or 41.3 ft-lbs.
• When torquing the fuel pump bolts, torque to 12Nm or 8.6 ft-lbs.

Refit the engine bay plastics

Now that you've replaced the high-pressure fuel pump, it's time to put everything back together.

First, refit the noise insulation pad back to the valve cover. Slide it under the two tabs at the back of the engine cover, and then press the rest into place.

Next, refit the lower cowl piece. Thread in its seven fasteners by hand before using a 10mm socket to tighten them.

After that, install the strut tower brace. Line it up and loosely thread in all of the bolts by hand to ensure you've aligned it correctly. Then, use an E18 socket to drive in and torque the bolts to 56Nm, plus 90° of rotation.

Now, reinstall the two upper cowl pieces. Slide them into place and use a 10mm socket to turn the three locks and secure the pieces to the car. Then, refit the plastic rivets on their outer edges.

Now you can refit the hood seal to the strut brace and run the cable through it. Then, refit the rubber strut covers and secure them with their plastic rivets.

Lastly, refit the engine cover. Reconnect the vacuum lines to the cover if your engine requires it.

Remove the radiator fan

To remove the radiator fan, you will need to follow these steps:

Firstly, you will need to remove the intake manifold. This will give you access to the radiator fan and the other components in this part of the engine. Next, you will need to lock the engine from rotating. This step is optional but will make it easier when putting the nut back on later.

Now, you can remove the 17mm hex bit cap from the front of the engine. There are two of them, so be sure to open the one on the right. Then, finger-tighten the ring portion of the special removal tool and screw it in. You will now be able to see the threads in the sprocket.

The next step is to loosen the jack bolt on the special tool and thread it onto the sprocket. You will need to finger-tighten it at first and then tighten it with a wrench. Now, screw in the jack bolt finger-tight and then tighten it further to pretension the pump.

At this point, you will need to remove the three nuts from the back of the pump, including the fuel lines. Crank on the jack bolt to push out the fuel pump. It should come out easily. Once the pump is released, back out the jack bolt and put it to one side, as you won't need it again.

Now that the pump has been removed, you can start to reassemble the parts in reverse order. Make sure to clean the surface of the pump and engine before replacing the metal gasket, ensuring that it is facing the correct way. Put the nuts back on at the back, being careful to keep the pump straight as you do so.

Finally, you can replace the radiator fan, ensuring that all the parts are secure and correctly positioned.

Frequently asked questions