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Fuel Pump pressure check E28 535i

symptoms of bad fuel pump pressure

  • Difficult to start
  • Sputtering engine
  • Engine stall
  • Power Loss
  • Poor fuel efficiency

Learning Context

The 1987 535i E28 is equipped with both an in-tank fuel pump and an external fuel pump to keep the fuel system under pressure. If either of these two pumps begins to fail or fail completely you will experience performance issues with your vehicle.

Why am I testing this?

I am testing the fuel pump pressure to ensure that the fuel pump is working properly and to rule this out as I diagnose an excessive fuel consumption issue.

Summary

  1. Relief fuel pressure
  2. Check for proper Fuel pump pressure( Engien off, fuel system energized)
  3. Fuel pump pressure reading= 92-100PSI(maximum)
  4. Fuel pump Hold pressure reading= 80PSI
  5. Tools require for the job
    • Pressure test kit
    • 6″ fuel-rated hose
    • Cleaning rags

Warning

Gasoline is extremely flammable, take proper precautions when working on any part of the fuel system. Don’t smoke, allow open flame, or use bare light bulbs near the area exposed to fuel. If you spill fuel on your skin, rinse immediately with soap and water, wear safety glasses, and have a class B fire extinguisher on hand.

Fuel Pressure relief procedure

Before you begin testing any part of the pressurized fuel system, you need to relieve any pressure that remains in the system.

  1. Locate and remove the fuel pump fuse from the Main fuse panel. If you are not sure where your fuel pump fuse is located consult your Owners manual, or take a look at my blog post about Fuse location(link to the blog post about the fuse box)
  2. Start the engine and wait for the engine to stall, then turn the vehicle off.
  3. Remove the fuel filler cap to relieve the fuel tank pressure
  4. The fuel system is now depressurized

procedure

  1. Disconnect the negative battery cable

2. Detach the fuel feed line from the fuel rail and attach a fuel pressure gauge(Warning: Do not use a plastic tee fitting for this test. It won’t be able to withstand the fuel system pressure.)

3. Attach the negative cable back to the battery. Bridge terminals #30, and #87 of the fuel pump relay.

4. Turn the ignition on and take note of the pressure reading on the gauge. Compare that reading to the pressure readings listed in the summary.

5. Turn the ignition off and wait 5 minutes keeping an eye on the pressure reading. Compare the hold pressure with the reading listed in the Summary.

6. Remove the jumper wire, relieve the pressure from the gauge, and reconnect the fuel hose to the fuel rail.

Conclusion

If the fuel pump fails the pressure and pressure hold test, check the fuel lines between the fuel rail and pump for any leaks. If no leaks are found the fuel pump needs to be replaced, once replaced perform the test again.

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