Checking Fuel Pressure

From BMW E34 Encyclopedia

Setup[edit]

You can tap in a fuel pressure gauge in the line going into the fuel rail from the driver side. Locate the fuse box near drive side mount and look behind it. You should see a metal fuel line connected with a clamp to a fuel hose running to the metal fuel rail on top of the engine.

Checking the fuel pressure.jpg

  1. Start the car
  2. Remove fuse number #22 (fuel pump), and wait for the car to choke
  3. Shut off the car and unplug battery (safety)
  4. Unscrew the clamp and take out the hose from metal rail near fuse box
  5. Put the hose into a pressure gauge on one end and use a piece of new fuel hose on another end and clamp it to the metal fuel line
  6. Make sure everything is tight
  7. Turn on the ignition in position number one to begin priming the pump at low pressure. Check for leaks
  8. Attempt to start the car by turning it over for 2-4 seconds at a time. You should check for system leaks between the attempts. The E34 will require about 4-5 attempts before the fuel pressure is up to the specification
  9. Read the fuel gauge

Specifications[edit]

  • 3.5 BAR, +/- .02 BAR
  • 50 PSI, +/- 3 PSI

Testing for leaks[edit]

After testing the fuel pressure, shut the car off and write down the current fuel pressure. Wait 20 minutes; the pressure should not drop more than 0.5 BAR.

If it does, you have a leak or faulty fuel pump check valve.