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Thread: Fuel pressure regulator fault?

  1. #1
    Join Date
    Feb 2006
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    Oldham, England
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    Default Fuel pressure regulator fault?

    My car starts first time, every time. Well until this morning. Turned the key, it ran for a few seconds and died. Wouldnt restart so I didnt want to flatten the battery trying and got a lift to work. I'm thinking fuel problem so tonight with a torch and +1 temp I check the fuel pump fuse and thats ok. So i jumper the fuel pump relay. I can hear the pump humming nicely under the boot carpet. But I can also hear fuel coursing through the pipes under the bonnet. Try to start it and get a cough. Encouraged I give it a few more goes and she will try to run but dies. I think I can smell fuel so I pull the jumper and replace the relay. Eventually she starts and idles normally. So two questions:
    1. Should I have heard fuel rushing round the pipes? I'm thinking it should reach pressure and then stop until the injectors release some pressure
    2. If I SHOULD hear it flowing, what did I do to to make her start?
    I've already ordered a fuel pressure gauge but as that wont be here by 6.30am (when I need the car again for work) I'd appreciate any advice pdq
    Last edited by whiskychaser; 12-10-2007 at 01:46 PM. Reason: forgot something

  2. #2
    Join Date
    Oct 2004
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    Honolulu
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    3,105

    Default

    Yeah, there should be some fuel return.

    The fuel system is a loop, pressurized up to the injectors and released to a return line via the regulator.


    Vee ave vays of dealing vid your kind...........

  3. #3
    Join Date
    Nov 2005
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    south central Canuck
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    Default

    No you should not really hear the hiss of rushing fuel. If you replace the pump with a new one the flow is quit. Time for a pressure check to let you know for sure. It is simple just 'T' into the the system before the pressure reg. I do it in the trunk @ the top of tank. Then I check the return for pressure should be no pressure in the return. The fuel bowl in the tank can clog at the exit of the return, causing very high pressure.
    Black tall pipes and poor gas mileage indicate high fuel pressure.
    The first thing I would do though is unplug the MAF and see if the car runs better. You will throw a code but most times the 92 MAF fails it does not throw a code. If the car runs normal then it is the Maf. If you still hear the hiss you may want to start looking for a fuel pump. The hiss usually means that there is not much flow thru the reg.
    525iT
    Not your Daddy's wagon

  4. #4
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    Default

    Quote Originally Posted by Sailor
    No you should not really hear the hiss of rushing fuel. If you replace the pump with a new one the flow is quit. Time for a pressure check to let you know for sure. It is simple just 'T' into the the system before the pressure reg. I do it in the trunk @ the top of tank. Then I check the return for pressure should be no pressure in the return. The fuel bowl in the tank can clog at the exit of the return, causing very high pressure.
    Black tall pipes and poor gas mileage indicate high fuel pressure.
    The first thing I would do though is unplug the MAF and see if the car runs better. You will throw a code but most times the 92 MAF fails it does not throw a code. If the car runs normal then it is the Maf. If you still hear the hiss you may want to start looking for a fuel pump. The hiss usually means that there is not much flow thru the reg.
    Thanks for the responses. I should make it clear I could only hear the rush of fuel when i jumpered the relay and the engine wasnt running. I have ordered a pressure gauge and that should arrive soon. My daily drive is only about 8 miles to work and back. The engine started fine this morning and tonight so at least I got to work and back. The OBC shows 14 mpg but that more than doubles if I a do a distance of say 60 miles, part on the motorway. Will warm up the lap top and see if any codes are stored. And report what fuel pressure I have when the gauge arrives. I can take a lot of stabs of what it MIGHT be but as the bugger now fires up as normal diagnosis is difficult. Apart from fuel pressure and stored codes, anyone care to add to the check list?

  5. #5
    Join Date
    Jan 2004
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    Thunder Bay, Ontario
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    The M50 should push ~50psi (M20-M30 ~43).

    I've tested the fuel pressure on mine in order to locate a stumbling on acceleration. I have a solid 50 psi from the pump. When the pump relay is 'jumped', I also hear the fuel gurgling through the lines. Mine has only failed to start once, and we're talking two years of very, very periodic issues. Fuel filter and pressure regulator are next on the list, then I might consider fooling with the pump again.

    I'll be watching this thread.

    Dave M

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  6. #6
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    Default

    Quote Originally Posted by Dave M
    The M50 should push ~50psi (M20-M30 ~43).

    I've tested the fuel pressure on mine in order to locate a stumbling on acceleration. I have a solid 50 psi from the pump. When the pump relay is 'jumped', I also hear the fuel gurgling through the lines. Mine has only failed to start once, and we're talking two years of very, very periodic issues. Fuel filter and pressure regulator are next on the list, then I might consider fooling with the pump again.

    I'll be watching this thread.

    Dave M
    Thanks for the response. I'm going to go about this methodically and intend to check the following:
    1. Fuel pressure with the relay jumpered - should be 51 psi +/-
    (If it isnt, intend to pinch the return to see if it increases)
    2. Fuel pressure after the letting the system stand for 20 mins
    (should be same)
    3. Fuel pressure with engine warm and idling-should be 51 psi +/- with vacuum hose disconnected from the regulator
    4. As 3 but with the vacuum hose connected.
    5. Vacuum at inlet manifold

    I expect the fuel pressure to reduce by about 0.5psi for every inHG of vacuum when the engine is at idle. Have it in my head I should be looking at 18 inHG so by my reckoning the fuel pressure would drop to 42 psi. Can anyone correct me on this plse?

  7. #7
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    Default Got my fuel pressure gauge

    Received it safe and sound. Ad and pack state its good for up to 300 psi. Until you take a look at the (white) upper scale on the gauge which shows a max of 10!! WTF? Supplier is 'checking it out'. Meanwhile a crap photo - cant seem to post them from a proper camera as files are too big:
    Attached Images Attached Images  

  8. #8
    Join Date
    Jan 2004
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    Thunder Bay, Ontario
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    1 bar or 1 atmosphere = ~14.5 psi. Could you be reading a bar or atmosphere scale?

    It would be one silly fuel pressure tester with a max of 10 psi.

    Dave M

    10/90 Build 525im, 630,000+km, Eibach/Sachs, Engine Rebuild
    *RIP Oskar the DOG *

  9. #9
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    Default Fuel pressure tester

    Quote Originally Posted by Dave M
    1 bar or 1 atmosphere = ~14.5 psi. Could you be reading a bar or atmosphere scale?

    It would be one silly fuel pressure tester with a max of 10 psi.

    Dave M
    Supplier got back to me this afternoon. To quote you, Dave 'Its one silly fuel pressure tester' -the max IS 10psi!!!. Sealey and Draper are doing the same gauge so anyone buying one beware. The good news is that the car is running. And I can test the inlet vacuum. So my next job is to find a tool that DOES what it says on the can

  10. #10
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    West of Cinci, OH
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    Default

    Carburated engines typically run less than 10 psi fuel pressure, and that's probably the type of gauge you received. You need an gauge for 'Fuel Injected' vehicles. Either way, the packaging is still incorrect.

    FWIW, I can't recall ever seeing a fuel pressure gauge that clears 300 psi, most stop around 100 psi.

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