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BMW E46 3 Series 1999 -2004 (323i, 325i/xi, 328i, 330i/xi, M3, conv, sport wagon) Low fuel pressure

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Last Post: Jul 17, 2014 12:00 PM Last Post By: eddieK

Posts: 1
Registered: 05/13/14
Low fuel pressure
Posted: May 13, 2014 10:56 PM
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My 2001 325i has a problem I need help with. Checking the fuel pressure at the fuel rail I only get about 10 psi. I've replaced the fuel filter/regulator and it made no difference...pressure remained at 10 psi. Checked the fuel pump operation and it checks out...12v for a couple of seconds to prime the system when the key is first turned on and then the pump comes on and pumps fuel when the key is moved to the start position. I disconnected the fuel pump and connected a hose from the pump to a cup to test this.

Question: Could the pump still be defective? Is there a fuel pump delivery measurement to be made? I have a good Bentley manual but it is very light on specific trouble shooting procedures.

Francis at Bent...

Posts: 30
Registered: 11/13/13
Re: Low fuel pressure
Posted: May 22, 2014 11:16 AM   in response to: Gman12 in response to: Gman12
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You could definitely have a faulty pump that will not build pressure. You should be seeing approximately 5 bar ( 70-75 psi) with the engine running, and it should not drop more than 10 psi in 20 mins after shut down. You can also perform a fuel delivery volume check, and a fuel pump power consumption check. The power consumption of the fuel pump with your meter in series should be approximately 8-13 amps. Too high or low of consumption means the pump is failing, meeting a restriction, or loosing pressure somewhere. With the correct fittings you can check fuel pressure directly at the tank as well if you think you have an issue in the fuel line. For volume, you can remove the schraeder valve from the fuel rail (check, they are often reverse rotation) attach a rubber line run into a measured container, supply power to the fuel pump, and make sure you see an adequate volume of fuel. A healthy pump should be able to flow about 2.5 liters in under min, but often will fill a gallon container much faster, so keep an eye on the container. I hope this helps.

Posts: 1
Registered: 10/04/06
Re: Low fuel pressure
Posted: Jul 17, 2014 12:00 PM   in response to: Francis at Bent... in response to: Francis at Bent...
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Whist a bit late to the party, it is paramount that volume tests are done at the pressure the system is designed to run at, i:e remove the return from the fuel rail to the tank and measure with the pump running at its designed pressure, the return flow should be a minimum of 1 ltr a minute.
It is no good just measuring the output from the pump directly, even a worn pump might produce something that way and mislead you.

Ed Kaps

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