Fuel system issue

Discussion in 'Technical' started by lolwut, Jan 15, 2018.

  1. lolwut

    lolwut Developing OCD

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    Sorry to make the title so vague but I have been having issues with my fuel system lately.

    My fuel pump was buzzing when it was priming, under load and when I shut off the engine. It was also humming lightly when idle of under no load. In addition to that, i would lose fuel pressure after about an hour of driving to the point where i would stuggle to even get up a hill. Quick fix to that was topping up the fuel to a full tank but the buzzing stays.

    So assuming the fuel pump was about to crap itself, I bought a brand new fuel pump and fitted it. It was fine when i first started the car again, until I went for a drive and the pump started buzzing even louder than the last pump did under load. Did an hour drive and same thing happened, just completely lost pressure and couldnt even accelerate at all. Limped it to a servo, topped it up to full and off i went again.

    At this point, I'm assuming its the fuel pump control unit being the culprit, but i couldnt find anything on the control unit and this kind of a symptom. Is it possible that the control unit is maybe overloading the pump and causing it to overheat and fail?

    Thanks in advance for the help
     
  2. rob260

    rob260 Moderator Staff Member

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    Definitely try bypassing the control unit. There is a blue wire coming off the top of the bulkhead and running to the harness connector. This is the earth wire for your pump. Interrupt it any way you can (cut it, use a wire tap, whatever work) and runnit directly to earth.
     
  3. brisz

    brisz Well-Known Member

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    Is the FPCU already bypassed ?

    This causes the pump to run at full speed all the time, lots of people have done it and seem to get away with it.

    Never thought it was a great idea though.

    The fuel actually helps keep the pump cool and ensure long life. As does the FPCU running at lower speed when suitable.

    When the FPCU is bypassed, the pressure regulator bypasses a lot more fuel, this flow takes away a lot of heat with it, fuel cooling your engine.

    This heat returns to the fuel tank, now your pump isn't running as cool.

    This becomes more of a problem as the fuel level is lower as the fuel is cycling through the engine bay more often.

    It will also be more of a problem on longer drives as the process is in play for longer.

    And really hot weather wouldn't help either. :rolleyes:

    Filling the tank up with cool fuel might help, a little out there but thought I would mention it.

    Generally the mode of failure for a FPCU is to not run.
     
  4. TWIN TERROR

    TWIN TERROR Well-Known Member

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    Fuel filter blocked ?
     
  5. MagicMike

    MagicMike Moderator Staff Member

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    Heard of tanks not having the correct venting and sucking themselves in. With this much vacuum the pump eventually can't pump out. When you release the fuel cap vacuum is released.

    Worth checking. Do you get a massive hiss when you undo the cap? Do you have a standard cap?

    What else can you tell us about your fuel system? Stock? It is unlikely a stock ish system is generating enough fuel temp to be an issue, but outside factors could be involved. I know excessive fuel temps can cause big issues from experience. Do you have access to consult/datascan? There is a fuel temp sensor in the rail (cant remember if these softwares can display it?). Getting some actual temps will help.

    Of course try the simple things first.
     
  6. East Coast Z

    East Coast Z Well-Known Member

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    "I would lose fuel pressure after about an hour of driving to the point where I would struggle to even get up a hill."

    Is this statement concerning the loss of fuel pressure a diagnostic fact, or an assumption?

    If you have actually measured the fuel pressure.
    How much pressure is at the rail when the drivability issue occurs?

    How much voltage is supplied to the pump when the issue occurs?

    How much fuel are you adding to the tank to get it going again?

    If the pump is faulty/defective, adding more fuel to the tank isn't going to help.
    Mikes suggestion concerning the fuel cap has merit & worth checking.
    It may be a case of a temporary fix occurs when you release the cap, rather than adding fuel.
     
  7. Fists

    Fists Well-Known Member

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    Ever changed the fuel filter? I'm assuming you installed a new filter sock with the new pump?
     
  8. rob260

    rob260 Moderator Staff Member

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    Hey Louis isn’t this the car that had the wrong bulkhead? Ie car is a 2+0 but it had a 2+2 bulkhead and hanger? Did you rectify that when you changed the pump?
     
  9. lolwut

    lolwut Developing OCD

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    Thanks for the help so far. I just had the car dropped off for transportation so I won't have the car with me to diagnose in the next few days.

    The FPCU isnt bypassed yet, it's still hooked up as per normal. The fuel system should be completely stock as far as i know but its hard to say anything else dodgy might have been done by the PO.

    I had the fuel filter changed about 2000kms ago but it could be that its blocked, i have yet to check that possibility.

    The fuel cap on the car is the factory fuel cap and when i release the fuel cap to top up the fuel, i don't remember there being a strong vacuum or pressure release but i will have to confirm that.

    The statement of loss of fuel pressure is an assumption due to it cutting out at higher rpms or heavy load, then struggling more and more and i try to accelerate to the point where it wont even get past 2k rpm.

    I have yet to measure the fuel pressure and voltage to the pump yet and i last topped up about 30 liters of fuel when it started cutting out.

    The fuel filter sock was changed with the new pump.

    The bulkhead and hanger was wrong initially and i swapped it out for a complete 2+0 bulkhead and hanger but when the pump that came with it also started buzzing, i figured it possible that the 2nd hand pump was failing as well hence the change to the new pump to see if it solved the buzzing issue.
     
  10. rob260

    rob260 Moderator Staff Member

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    Is the siphoning system plumbed in correctly? If not you’d only have access to half the fuel in the tank
     
  11. IB

    IB ?????

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    I destroyed two tanks before I worked out the cap didn't have vacuum relief. I never had any fuel pressure issues.
     
  12. geron

    geron National Petroleum Equipm

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    Just a little off topic, but kind of relevant, when a Walbro pump is hooked up the correct way, I believe the pump works @ full stick all the time, which means the fuel is constantly circulating and heating up. Would that mean that the FPCU is bypassed? On hot days the fuel reaches 50+°C
    Just curious.
    I'm asking b/c many years ago, the OEM fuel pump died and UAS put in a Walbro unit and I can't remember if the FPCU was bypassed or not. I read somewhere that when putting in a Walbro pump a small wiring modification is done at the pump stage only to ensure they last a long time and the FPCU is left alone but I'm not sure now.
    I'm thinking, if I ever need to install an OEM pump, if I have to also rip out the rear LHS trim to get to the FPCU which is a PITA.
    Any ideas?
     

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