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Pelican Technical Article:

Fuel Pump Testing

Nick Czerula

Time:

3 hours3 hrs

Tab:

$300

Talent:

*****

Tools:

10mm socket, DVOM, test light. Fuel pressure gauge

Applicable Models:

BMW X5 (2000-06)

Parts Required:

Fuel pump, fuel pump-sealing O-ring

Hot Tip:

Clean top of fuel tank before removing pump

Performance Gain:

Repair faulty fuel pump

Complementary Modification:

Fuel filter is not serviceable

The fuel supply system in a BMW E53 consists of:

  • Fuel tank
  • Fuel filler with associated breathing and venting pipes
  • 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 left fuel tank lobe holds the fuel level sender, while the right tank lobe holds the fuel pump.

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. You can access terminals under the rear seat cushion, below the access panel.

Replacing the fuel pump on a BMW E53 can be done without removing the fuel tank. There are access panels under the rear seat cushion that allow servicing. It is best to replace your fuel pump with the fuel tank drained. This reduces the amount of possible spilled fuel and fuel vapors. When replacing, work in a well-ventilated area. Working outdoors is a good choice. Do not use incandescent work lights or power tools. Fuel and fuel vapors are highly combustible.

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.

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.

The fuel pump /sending unit is located in the right (green arrow) side of the fuel tank.
Figure 1

The fuel pump /sending unit is located in the right (green arrow) side of the fuel tank. The sending unit / siphon jet pump is located on the left (red arrow) side.

Pressure testing: 
Pressure testing: Remove the engine cover over the fuel injectors.
Figure 2

Pressure testing: Remove the engine cover over the fuel injectors. See our tech article on engine covers removing. Remove the fuel test port cap (red arrow). The 8-cylinder engine is shown. The 6-cylinder engine test cap is at the front of the fuel rail.

Pressure testing: Install the fuel pressure gauge (red arrow).
Figure 3

Pressure testing: Install the fuel pressure gauge (red arrow). Be sure that all the test hoses are installed and routed properly.

Pressure testing: Next, start or attempt to start the engine.
Figure 4

Pressure testing: Next, start or attempt to start the engine. Fuel pressure should be 3.5 bar +/- 0.2 (50 psi +/- 3). If the engine starts, expect pressure to be about 0.5 bar lower than engine off pressure. 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 (red arrow) bar in that time period. If it drops you could have a faulty fuel pump check valve or a leak in the fuel system.

Electrical testing: 
Electrical testing: 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 5

Electrical testing: 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. Once you have removed the rear seat, cut the insulation straight back in the marked locations (green arrows). Then remove the four 10mm nuts (red arrows) from the fuel pump access panel.

Electrical testing: Remove the access panel lid from the body by lifting it up.
Figure 6

Electrical testing: Remove the access panel lid from the body by lifting it up. Be sure to replace the panel gasket if it is damaged. Disconnect the fuel pump electrical connector (red arrow) by sliding the lock to the right side of the vehicle (inset) and lifting it off.

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

Electrical testing: 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 two large wires at the connector.

Electrical testing: Turn the key ON.
Figure 8

Electrical testing: Turn the key ON. The DVOM should read battery volts (around 12 volts) (red arrow). Mine is reading a little higher because I have a vehicle power supply connected. 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 engine doesn't start).

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

Electrical testing: 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 backprobing 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.

Electrical testing: You can also jump out your fuel pump relay (to bypass it) for testing.
Figure 10

Electrical testing: You can also jump out your fuel pump relay (to bypass it) for testing. The vehicle used in this tech article was a 2003 X5 with an 8-cylinder engine. The fuel pump relay position varies depending on year. See the list below for relay locations. Double check your fuel pump relay location with the latest BMW repair information. Under the right side of the dashboard on the relay panel, remove the glove box. See our tech article on glove box removing. Once the glove box is out, remove the four T20 Torx screws at the fuse and relay panel (red arrows).

Electrical testing: Pull the fuse and relay panel down.
Figure 11

Electrical testing: Pull the fuse and relay panel down. The fuel pump relay is green and located at the end of the under dash relay panel (red arrow).

Electrical testing: Remove the fuel pump replay.
Figure 12

Electrical testing: Remove the fuel pump replay. Connect a fused jumper wire (red arrow) between the terminals indicated by the arrows. The green arrow points to terminal 30 (battery positive). The yellow arrow points to terminal 87 (fuel pump feed). This will activate your fuel pump. Check for voltage at the fuel pump as you did earlier. Battery volts should be present. Terminals may vary; double check your model against a wiring diagram. This photo shows the bottom of the relay. It has the terminals noted. It will help you identify the correct terminal.

Electrical testing: You can also check the relay circuit using a digital multi-meter (DVOM).
Figure 13

Electrical testing: You can also check the relay circuit using a digital multi-meter (DVOM). Connect the black lead of your DVOM to battery negative, and use the other to backprobe the terminals. Use the following list to cross reference your voltage readings. Keep in mind that wire colors and positions may vary depending on year and engine. What you see below is from my 2003 X5 8-cylinder. Other readings should be similar: Red arrow: Terminal 30 - constant battery positive; Yellow arrow: Terminal 86: switched battery positive, present when key is in ON position; Blue arrow: Terminal 85: DME relay control, close to zero volts when DME turns relay on; Green arrow: Terminal 87 - Feed to fuel pump, battery positive when relay is activated.




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Comments and Suggestions:
Wes Comments: There is no power going to my fuel pump from the battery wires the two bigger wires. I bypassed the power from the relay connectors, as you suggested, and the pump was running without issues. What is the next step to get the car to start, now that I know it is a fuel pump power issue? Thank you for your help, any help would be greatly appreciated.
December 7, 2016

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Page last updated: Fri 12/9/2016 02:56:54 AM