Relieving Fuel Pressure In A Mini Cooper

If you are experiencing issues with your Mini Cooper's fuel system, it may be time to release pressure from the fuel system. This can be done by following these steps:

- Disconnect the negative battery terminal.

- Remove the air box by unscrewing the Torx head screws and detaching the intake hose.

- Clear the area around the High-Pressure Fuel Pump (HPFP) by moving small hoses and electrical connectors out of the way.

- Ensure that rags or towels are placed around the connection area to prevent fuel spillage.

- Using a 1/16 punch, press the black pin on the input fuel line and push the quick-release connector towards the HPFP. Then, pull back on the fuel line to release it.

- Wrap a rag around the threaded fitting and remove the fuel line with a 12mm line wrench.

- Remove the three screws holding the HPFP in place using a T30 Torx bit, extension, and ratchet.

- Disconnect the electrical plug on the bottom of the HPFP and pull the pump away from the motor.

- Place a new pump next to the old pump and align the new pump drive to match the angle of the old pump drive for easier insertion.

- Ensure the O-ring seal is in place on the pump housing and rub a small amount of oil on it to prevent pinching.

- Place a small amount of oil onto the two fuel line seals and connect the threaded line to the pump finger-tight.

- Push on the other fuel line and place the pump in the pump drive on the cylinder head, aligning the screw holes.

- Replace the three screws to hold the pump loosely in place and check that the pump is seated correctly and sitting flat on its mounting surface.

- Torque the mounting bolts to the specified values for your engine.

- Reassemble any hoses or lines that were moved or removed to access the HPFP.

- Reattach the junction block, intake hose, and air box.

- Reconnect the negative battery lead and prime the pump by cranking the motor for 15 seconds at a time, three times.

- Start the engine and run it for five minutes to warm up.

- Check for leaks and fix as needed. You may need to replace the fuel lines.

How to check the fuel pressure

To check the fuel pressure in your Mini Cooper, you will need a fuel pressure gauge. This can be attached to the fuel rail test port, which is located on the right side of the fuel rail, just below the intake air housing outlet.

Step 1: Locate the fuel rail test port. It is usually found on the right side of the fuel rail, below the intake air housing outlet.

Step 2: Remove the fuel test port cap. This is typically a Schrader valve located behind the cap.

Step 3: Install the adapter and fuel pressure gauge into the valve. Ensure that all test hoses are installed correctly and routed properly.

Step 4: Start or attempt to start the engine. For turbocharged models, the fuel pressure should be 5 bar (72.5 psi). For normally aspirated models, the fuel pressure should be 3.5 bar (50.7 psi).

Step 5: Recharge the fuel system by cycling the key or running the fuel pump. Take note of the fuel pressure reading.

Step 6: Allow the fuel system to sit under pressure for 15 minutes. The pressure should not drop more than 0.5 bar during this time. If it does, there may be a faulty fuel pump check valve or a leak in the fuel system.

Step 7: If the fuel pressure holds steady and does not drop significantly, your fuel system is likely functioning correctly.

It is important to consult your vehicle's repair manual for specific instructions and fuel pressure specifications, as they may vary depending on the model and year of your Mini Cooper.

How to replace the fuel pump

Step 1 – Disconnect the battery

Disconnect the negative (black) battery terminal. When working with fuel and its explosive vapours, it is important to do so. The battery is located under an access panel on the passenger side, up by the windshield.

Step 2 – Remove the air box

• Remove the three Torx head screws in the air box.
• Unscrew the hose clamps holding the intake hose to the air box, then remove the hose.
• Unplug the electrical connector to the mass airflow sensor (MAF).
• Remove the air box and set it aside.

Step 3 – Clear the area around the High-Pressure Fuel Pump (HPFP)

• Move all small hoses and electrical connectors that block access to the HPFP.
• Pull up on the junction block and move it as far as the slack in the lines allow.

Step 4 – Remove fuel lines from HPFP

• Place rags or towels around the connection area to prevent fuel spillage, as some may leak or spray out.
• Using the 1/16" punch, press the black pin on the input fuel line on the passenger side.
• With the pin pressed in, push the quick-release connector toward the HPFP, then pull back on the fuel line to release it.
• Wrap a rag around the threaded fitting and remove the fuel line with the 12mm line wrench.
• These fuel lines should be replaced whenever they are removed to ensure proper sealing.

Step 5 – Replace HPFP

• Using the T30 Torx bit, extension, and ratchet, remove the three screws holding the HPFP in place.
• Disconnect the electrical plug on the bottom of the HPFP and pull the pump away from the motor.
• Place the new pump next to the old pump and align the new pump drive to be at the same angle as the old pump drive for easier insertion.
• Ensure the O-ring seal is in place on the pump housing, and rub a little oil on it to help prevent it from getting pinched.
• Place a small amount of oil onto the two fuel line seals.
• Connect the threaded line to the pump finger-tight, then push on the other fuel line.
• Place the pump in the pump drive on the cylinder head, and align the screw holes.
• Replace the three T30 bolts to hold the pump loosely in place, but do not tighten them yet.
• Check that the pump is seated correctly in the drive and sitting flat on its mounting surface.
• Torque the mounting bolts to the specified values for your engine type.
• Torque the threaded fuel line using the 12mm crow's foot socket.
• Reassemble any hoses or lines that were moved or removed to clear a path to the HPFP.
• Reattach the junction block, intake hose, and air box.

Step 6 – Start the engine

• Reconnect the negative battery lead.
• Prime the pump by cranking the motor for 15 seconds at a time, three times.
• Start the engine (it may take several tries before the HPFP is full of fuel again).
• Once started, run the engine for five minutes to warm up.
• Check for leaks and fix them if necessary. You may need to replace the fuel lines.
• If your engine is an N14, disconnect the battery, remove the air box, and re-torque the fuel line to its final tightness.
• Replace the air box and reconnect the battery.

How to replace the fuel filter

Step 1 – Disconnect negative battery lead

• Open the hood and lift the access cover by the windshield on the passenger side to get to the battery.
• Disconnect the negative (black) battery lead.
• This will prevent any sparks or inadvertent startup of the fuel pump while working on the filter, which would cause a major fuel spill and a perilous amount of cleanup.

Step 2 – Remove the rear seat

• The hardest part of this job is removing the rear seat in order to get to the access panels.
• Fold the seat backs forward, and press the release latch on the central pivot, which holds both seat backs.
• Lift the pivots out, one seat back at a time, and fold them back upward to 45 degrees, which will allow the outside pivot to slide free.
• Repeat for the other seat back.
• The lower cushion is held in place by clips on the floor. Pull out the plastic grommets for the child seat anchors.
• Reach under the front edge and pull up to release it. With the front loose and angled up, press down in the center of the seat to pop the rear hook free.

Step 3 – Remove access panel

• The filter is located under the rear seat on the passenger side of the vehicle.
• Once the seat is removed, the access panel to the fuel filter can be seen.
• Remove the 10mm nuts that surround the exterior of the panel.
• Using a flat tip screwdriver, pry up on the cover to remove it from the body.
• This will expose the top of the fuel tank and the filter.

Step 4 – Remove locking ring

• Brush or blow away any dirt or debris which may have gathered around the filter housing so it doesn't fall into the tank.
• Gather some paper towels and pack them loosely around the fuel line connection.
• Using needle nose pliers, push in on the sides of the fuel line connector tab, then pull and twist the fuel line to remove it.
• When this happens, a small amount of fuel will discharge from the connector.
• Before removing the locking ring, mark both the ring and on the access hole edge so you can tighten the ring down to the same approximate torque afterward.
• Using a flat tip screwdriver and hammer, place the screwdriver tip against the edge of one of the ridges.
• Tap the screwdriver to rotate counterclockwise. Do this gently and be patient with it as it turns.
• Continue to tap on the cap until it comes free and set it aside.

Step 5 – Replace filter

• The plastic canister that the fuel filter is in comes apart in two pieces, with several O-rings keeping them sealed.
• Hold the base of the filter canister with one hand, or a pair of oil filter pliers, and twist the lid counterclockwise a 1/4 turn.
• You may find a screwdriver in the slot just below the fuel line that helps you to turn it.
• Then gently pry the top away from the base. This may be a little difficult because the O-rings can get stuck, so it may take some persuasion to make it happen.
• Be careful as you pop the lid off, as there is still plenty of fuel left in the canister and it may spill all over the place.
• Once the lid is off and set aside, twist and pull the old filter to remove it from the canister housing.
• Once removed, get the turkey baster and suck out all of the dirty old fuel left, depositing it into the used fuel container.
• Clean out any residual dirt in the bottom of the canister with a clean rag, making it as clean as possible.
• Inside the canister, there are three O-rings which need to be replaced: two on the lid and one inside the lower canister.
• Once installed, place a thin layer of Vaseline on the O-rings to help everything slide into place easier.
• Push the new filter into place into the canister housing and be sure to get it to insert all the way.

Step 6 – Close up everything

• Place the lid back onto the canister housing with the locking tabs in their proper slot, then twist a 1/4 turn clockwise to lock it.
• Lowering the canister back into the fuel tank with the rubber gasket in place on the fuel tank flange.
• Be careful as you replace the canister not to damage the gasket, as it is easily torn.
• With the canister in place, put the locking ring back and turn back to the original position to lock it into place.
• Reconnect the fuel line.
• Reconnect the battery and turn the ignition on/off several times to cycle the fuel pump and refill the canister with fuel.
• It may be a little hard to start the car at first due to air being in the line. Don't crank the starter for more than 10 to 15 seconds at a time to prevent burning it out.
• Once started, let the car run and check the work area for leaks.

How to check the fuel pressure sensor

To check the fuel pressure sensor, you will need to use a scan tool to monitor the desired and actual fuel rail pressure. If the desired and actual fuel rail pressure do not match, then the fuel pressure sensor may be faulty.

• Connect a scan tool to the vehicle's OBD-II port.
• Locate the fuel pressure sensor, which is mounted on the fuel rail of turbocharged engines.
• Start the engine and allow it to reach operating temperature.
• Monitor the desired and actual fuel rail pressure values on the scan tool.
• Compare the desired and actual fuel rail pressure values. They should be close to each other. If they are significantly different, then the fuel pressure sensor may be faulty.

It is important to note that there are other factors that can affect fuel rail pressure, such as a faulty fuel pump or a clogged fuel filter. Therefore, it is recommended to diagnose and rule out other potential causes before concluding that the fuel pressure sensor is faulty.

How to replace the fuel pressure sensor

To replace the fuel pressure sensor on your Mini Cooper, you will need a set of sockets (10mm, 13mm), a flathead screwdriver, a fuel rail pressure sensor, a fuel line, an intake manifold gasket and related fasteners.

• Disconnect the negative (-) battery cable.
• Remove the intake manifold.
• Before removing the sensor, the fuel rail pressure needs to be relieved. Unplug the in-tank fuel pump and run the engine until the vehicle stalls.
• Work with a cool engine.
• Cut the tie straps and remove the harness from the fuel rail.
• Disconnect the electrical connector by lifting the tab and pulling it straight off.
• Loosen the sensor 1/2 a turn. The sensor hex boss is 27mm. Use an adjustable wrench as it fits better into the engine compartment.
• Unscrew and remove the sensor from the fuel rail.
• Reverse these steps to install a new sensor. Remember to use new seals and gaskets. Also, replace the high-pressure fuel line.
• Clear any fault codes when complete.

Frequently asked questions