Petrol fuel pump operation question
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Thread: Petrol fuel pump operation question

  1. #1
    Fellow Frogger! Big Frog's Avatar
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    Default Petrol fuel pump operation question

    Hi all,
    Modern petrol fuel injected cars typically have a submerged pump in the tank, that incorporates the fuel sender, and sends fuel under pressure to the injectors.
    My question is how is the pressure regulated? I know with our Berlingo, you hear the pump run then stop when the ignition is turned on, presumably it stops when the pressure is sufficient in the injector rail / system?
    How is this done? Is there a sensor in the fuel rail, or is there a mechanism in the fuel pump body?
    Or does the pump cycle once when key is turned, and then runs continually during operation with excess flowing back to tank?
    Steve

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    Last edited by Big Frog; 4th January 2019 at 11:40 AM.

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    Hi Big Frog
    Good question ! The computer turns on the pump for < minute in a petrol engine, then turns if off. This should prime the system to pressure but that is not measured. It is turned off any time the engine is not running for safety reasons.
    The pump normally run all the time when the engine is running, the petrol pressure is set by a regulator somewhere in the system, at the fuel rail, at the filter or or in the tank, the excess goes back to the tank. Later practice is to not send it to the engine area to limit heating the fuel for emission reasons.

    So you will see the in-tank unit has one, two or three hoses at the top. If it only has one then the regulator is in the tank also.

    If the regulator is on the fuel rail at the motor it usually has a vacuum hose on it to modulate the fuel pressure also.
    Jaahn
    PS diesel engines do have pressure sensors in the fuel supply.
    Last edited by jaahn; 4th January 2019 at 01:26 PM.

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    Fellow Frogger! Big Frog's Avatar
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    Thanks for explaination.
    It makes complete sense, I think in the Berlingo I recall a small silver can device as a part of the in tank pump unit, this must be some sort of restrictor / regulator to hold a certain pressure in the feed pipe.
    Cheers
    Steve

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    Here is a PSA regulator. It contains a spring which releases fuel back to the tank if it is overstrained, and adds some force if the lift pump pressure fluctuates. Similar devices are used to control water supplies.
    regulator.jpg

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    Hi
    Here is a short video !https://www.youtube.com/watch?v=g9QlOiovQxM
    Remember though that most information on the net is american and the actual details of these items and placement is not the French way
    Jaahn

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    Fellow Frogger! Big Frog's Avatar
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    Thanks SS & J,
    All makes sense, it's a purely mechanical device.
    My Berlingo sometimes randomly does not start.
    Have been eliminating causes. My current theory is that the relay that controls the fuel pump is dodgy. Unfortunately the relay is hard soldered to a board with others on the BSM.
    You can hear when the fuel pump cycles before starting and when it doesn't is usually when it won't start. The fuel rail has a Schrader valve, when it won't start, testing it by depressing it shows no fuel pressure.
    Anyhow I now can eliminate the regulator.
    I'm awaiting another BSM to arrive to swap.
    Thanks
    Steve
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    Check and clean electrical connections to the fuel pump ,pugs

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    Hi
    Yes my daughter had an R19 which had a habit of not starting at one point and I played with the pump to get it going again. In the end I did it properly and found the connectors at the pump were dodgey and I fitted a new(used) connector on the wires and made sure they were clean and tight. Problem solved till sold years later ! Of course it was a less tech control system probably just a normal relay.
    Good luck Jaahn

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    Fellow Frogger! Big Frog's Avatar
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    Thanks guys,
    I have some contact cleaner, will give it a clean.
    I really hate intermittent faults, so hard to trace, when it's working then not working.
    S

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    BTW
    one odd aspect of the issue is that the vehicle has never cut out whilst running. So if there was an intermittent connection with the fuel pump wiring I would have expected it to cut out at some time whilst running?
    S

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    Are you saying the problem is only at start up .next time it douse it ,turn the ignition on and off a few times to run the pump, then crank ,if it starts right up ,,fuel is running back to tank when standing ,are you sure the in tank pump is supplying pressure or is it just a lift pump that supplies the pressure pump further forward ie [under the passenger side floor ],we had an old volvo like this ,and i think 505 is the same ,what car are we talking about here ,

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    Check the pins and sockets at the BSM (engine fuse box) side as sometimes the fuel pump 12v pin can be burnt from heating. Colour from fuel pump will relate to BSM if you dont have a wiring diagram.
    Let us all know how you get along.

    Sent from my SM-G900I using aussiefrogs mobile app

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    Fellow Frogger! Big Frog's Avatar
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    Hi Pugwash
    The vehicle is an 06 petrol Berlingo, it only has the tank pump, turning the key doesn't always cycle the pump, only if it has been sitting, not sure that it doesnt have some timer that knows how long since it primed. 90 % of the time it works fine. Interigating the engine software says, Permanent fault - Actuator relay stuck.
    Great message, actuator is about the vagueist description possible, may as well say the rooster crowed at midnigbt!

    Thanks Dimistyle , will have a close look at the pins, do you know is which of the big plugs it's in? Black , grey or green?
    S

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