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Pelican Technical Article:

Fuel Pump Testing

Nick Czerula

Time:

3 hours3 hrs

Tab:

$0

Talent:

*****

Tools:

Phillips & flathead screwdriver, socket set

Applicable Models:

R52 MINI Cooper Convertible (2007-08)
R52 MINI Cooper S Convertible (2007-08)
R56 MINI Cooper Hatchback (2007-11)
R56 MINI Cooper S Hatchback (2007-11)
R57 MINI Cooper Convertible (2009-11)
R57 MINI Cooper S Convertible (2009-11)

Parts Required:

Fuel pump, fuel pump sealing O-ring

Hot Tip:

Check fuse before digging too deep

Performance Gain:

Properly functioning fuel pump

Complementary Modification:

Replace fuel filter

The fuel supply system in a MINI R56 consists of:

  • the fuel tank
  • the fuel filler with associated breathing and venting pipes
  • the high pressure fuel pump assembly with fuel filter and fuel level senders

The fuel tank is two-lobed. There are two fuel level senders, one in each lobe on the left and right sides underneath the rear seat cushion. The right fuel tank lobe holds the fuel level sender and fuel filter, while the left tank lobe holds the fuel pump.

In tank fuel pumps have many benefits. The fuel is submerged in fuel keeping it cool, preventing vapor lock and electrical issues. The fuel pump delivers a constant flow of gasoline to the fuel rail at a regulated pressure and volume. The fuel pump draws fuel from the fuel tank and pushes it through the fuel filter, mounted outside of the fuel tank.

A faulty fuel pump can cause poor engine performance and hard starting problems. When it fails completely, you may be left with an engine that doesn't start. If you suspect your fuel pump has failed, you can confirm the fuel pump has received the correct voltage when commanded ON by the fuel pump relay using a digital volt ohm-meter (DVOM). If the correct voltage is present, but the pump does not activate, it is likely faulty. Use the DVOM in conjunction with a wiring diagram to determine the correct terminals for testing.

Accessing the fuel pump terminals can be done without removing the fuel tank. There are access panels underneath the rear seat cushion that allow servicing. The fuel tank is two-lobed. There are two fuel level senders, one in each lobe on the left and right sides underneath the rear seat cushion. The left fuel tank lobe holds the fuel level sender and fuel filter, while the right tank lobe holds the fuel pump.

To avoid marring the paint and trim, work with a plastic prying tool or wrap a screwdriver tip with masking tape before prying out body or interior items.

Keep in mind that when your car was serviced before, parts may have been replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have, so be prepared with different size sockets and wrenches.

When performing electrical tests, be sure to use a digital instrument such as a DVOM. Using an analog device may lead to damage to sensitive electronic components.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Do not work on your vehicle if you feel the task is beyond your ability.

Vehicle models change and evolve, as they grow older, so the vehicle shown in our illustrations may vary slightly from yours. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

Depending on your model, turbocharged or normally-aspirated, you have a few options for fuel pressure testing.
Figure 1

Depending on your model, turbocharged or normally-aspirated, you have a few options for fuel pressure testing. On both models you can test the in tank fuel pump pressure using a test adapter. For example, on normally-aspirated models, you can attach a screw in type adapter (yellow arrow) into the fuel rail test port. On turbocharged models, the fuel system does not have a test port. So you have to use a T-adapter (red arrow) to test the in tank fuel pump. On turbocharged models, you can also test the cylinder head mounted high-pressure fuel pump using a MINI scan tool.

Models with turbocharged engine: Follow the fuel tank supply to the high pressure fuel pump (red arrow) down to the subframe junction (yellow arrow).
Figure 2

Models with turbocharged engine: Follow the fuel tank supply to the high pressure fuel pump (red arrow) down to the subframe junction (yellow arrow). Press the button and pull the fuel lines apart. Install your T-adapter here. Install the fuel pressure gauge. Be sure all test hoses are installed and routed properly. Next, start or attempt to start the engine. Fuel pressure should be 5 bar (72.5 psi). Once you test pressure recharge the fuel system by cycling the key or running the fuel pump. Note the fuel pressure. Then allow the fuel system to sit under pressure for 15 minutes. Pressure should drop no more than 0.5 bar in that time period. If it drops you could have a faulty fuel pump check valve or a leak in the fuel system.

Models with normally aspirated engine: Locate the fuel rail test port (red arrows) at the right side of the fuel rail, just below the intake air housing outlet (yellow arrow).
Figure 3

Models with normally aspirated engine: Locate the fuel rail test port (red arrows) at the right side of the fuel rail, just below the intake air housing outlet (yellow arrow). Remove the fuel test port cap (red arrow) Schrader valve located behind cap. Install the adapter and fuel pressure gauge into valve. Be sure all test hoses are installed and routed properly. Next, start or attempt to start the engine. Fuel pressure should be 3.5 bar (50.7 psi). Once you test pressure recharge the fuel system by cycling the key or running the fuel pump. Note the fuel pressure. Then allow the fuel system to sit under pressure for 15 minutes. Pressure should drop no more than 0.5 bar in that time period. If it drops you could have a faulty fuel pump check valve or a leak in the fuel system.

Working in the rear of the vehicle interior, grab the corner of the rear seat cushion and pull it up to detach the locking tabs.
Figure 4

Working in the rear of the vehicle interior, grab the corner of the rear seat cushion and pull it up to detach the locking tabs. Remove the seat cushion from the vehicle. See our tech article on seats removing. The fuel pump /sending unit is located in the left (green arrow) side of the fuel tank. The sending unit / fuel filter / siphon unit are located on the right (red arrow) side.

Once you have removed the rear seat, remove the four 10mm nuts from the access panel (red arrows).
Figure 5

Once you have removed the rear seat, remove the four 10mm nuts from the access panel (red arrows). Remove the access panel lid from the body by lifting it up. Be sure to replace the panel gasket if it is damaged (inset).

Working at the fuel pump housing, remove the electrical connector (red arrow) by sliding the lock as you pull the connector up.
Figure 6

Working at the fuel pump housing, remove the electrical connector (red arrow) by sliding the lock as you pull the connector up.

Connect the DVOM across the fuel pump terminals (red arrows).
Figure 7

Connect the DVOM across the fuel pump terminals (red arrows). These are the two terminals on my subject vehicle. You will be testing voltage across the large wires at the connector. Look for the two larger wires. Use a wiring diagram for your vehicle to be sure you are on the right wire.

While connected to the fuel pump connector (red arrow), turn the key ON.
Figure 8

While connected to the fuel pump connector (red arrow), turn the key ON. The DVOM (yellow arrow) should read battery volts (around 12 volts). If no voltage is found, check the relay and fuel pump fuse. With the key ON, the fuel pump will receive voltage for three to five seconds to prime the system (if the engine doesn't start).

I suggest load testing using a test light and a DVOM.
Figure 9

I suggest load testing using a test light and a DVOM. Connect the DVOM across the fuel pump electrical connector terminals and take a reading. It should read battery volts when the key is turned ON. Then connect an incandescent bulb style test light to battery ground and touch the test light probe tip to the positive wire you are back probing with the DVOM. Your reading should hold steady; a maximum drop in voltage of 0.5 volts is OK. Anything more is a problem. In this photo, voltage held steady. You can also jump out your fuel pump relay (to bypass it) for testing. As you can see, my subject vehicle dropped over 4 volts. That indicated a problem with the wiring, I found a corroded wire in the harness under the vehicle. The vehicle used in this tech article was a 2008 Cooper S. The fuel pump relay position varies depending on year. The relay on my vehicle is located in the junction box and gets power from a fuse in the junction box, F46 20 amp. Double check your fuel pump relay location with the latest MINI repair information. The relay is integrated into the junction box electronics. If you need to bypass it for testing, use a fused jumper wire from fuse F46 to the fuel pump power terminal. If it works the fuel pump and voltage holds steady, the relay is faulty.

You can check the high pressure system on turbocharged models using a MINI scan tool.
Figure 10

You can check the high pressure system on turbocharged models using a MINI scan tool. Use the scan tool to view DME, then fuel pump / pressure. Look for the rail pressure set point (desired) and rail pressure actual. These two values should be pretty close. If it's off by 10 bar, I would suspect a faulty high pressure fuel pump.


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Comments and Suggestions:
racemini Comments: Hi Nick! I have a base model r56, and I'm trying to diagnose why my car intermittently coughs and loses power at highway speeds and while going uphill on the highway. Right now, I suspect the engine isn't getting enough fuel on the highway.

I checked the voltage at the fuel pump relay during starting, and I got around battery voltage ~12.6 volts. However, when I check pin #2 of the fuel pump connector figure 8 of your instructions during starting, I get only 11.3 volts. Does this mean there's an issue with the wiring, as the pin is not receiving the full battery voltage? I tried measuring resistance from the relay to the fuel pump connector, and from the fuel pump connector to ground, but didn't measure any significant resistance.

If there is an issue with the wiring, how can I access the wiring to inspect it? I have the bentley manual, but I'm unsure where the fuel pump wiring runs through.
October 8, 2016
  Followup from the Pelican Staff: Could be low depending on where your ground is. Make sure the ground is on battery negative when testing.

If you suspect an issue with the wiring, confirm it via testing, loading the power and grounds or voltage drop test them. Then replace the wires if found faulty. Don't repair, just run new wires. It is faster. - Nick at Pelican Parts
 

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