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fuel pressure dropping

This is a discussion on fuel pressure dropping within the General Help forums, part of the LSx Technical Help Section category; Okay, the motor keeps bogging down and shutting off randomly. Already changed filter, dropped the tank and inspected the strainer. ...

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    Member joedude02's Avatar
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    fuel pressure dropping

    Okay, the motor keeps bogging down and shutting off randomly. Already changed filter, dropped the tank and inspected the strainer. I noticed that 1 fuel line had dirty fuel but it wasn't the line to the filter. It had the same type of line disconnect though. I purged a dry gas(nitrogen) thru the fuel rail and could hear good passage to the tank. What is this other fuel line? I think my problem is that. Help please, my baby is hurtin

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    I assume it is the return line.

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    Moderator Cutlass's Avatar
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    any pics of the line in question? maybe you are talking about the EVAP line?

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    Member joedude02's Avatar
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    Quote Originally Posted by pajeff02 View Post
    I assume it is the return line.
    The problem that I've found, but don't understand is that the return line is building up a lot of pressure and I guess that's causing issues with the regulator. I'm thinking something is clogged but I can't find it. I can release the quick disconnect to release the pressure and everything runs smooth for a few hours. What are your thoughts guys?

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    Senior Member JayTA98's Avatar
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    isn't a pressure regulator or valve at the pump? If the regulator or valve itself is clogged up it will cause the pressure build up.
    Last edited by JayTA98; 07-17-2010 at 08:42 AM.

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    Member joedude02's Avatar
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    Is the regulator just above the pump? Any ideas how to clear it?

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    Have you attached a fuel pressure gauge to the rail to get a reading yet?

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    Member joedude02's Avatar
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    Yes I have checked the pressure readings. First thing I did before dropping the tank the first time. When the problem occurs I have anywhere from 30 to 45 psi. sometimes as low as 25. Whenever I release the pressure from the return line under the rear end and retest, it goes back to 60 psi. I know the pump is still good. The return line goes to a metal rod that is part of the sending unit assembly. I guess that drains back into the tank right? The only part I think I can throw at this problem is maybe change out the regulator. Am I on the right track?

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    Member joedude02's Avatar
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    I tried just earlier to pressurise the return line leading into the tank. I can't get any pressure through. What is this path consist of exactly? I should have a clear path in the same direction that the return fuel follows correct?

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    Moderator Cutlass's Avatar
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    Ok the way the fuel system works on your car is:
    The pump pressurizes gas and it flows towards the fuel filter
    Then it flows through the fuel filter and a couple inches away is a T fitting
    One line off that T fitting is a return loop back to the tank.
    The Fuel Pressure Regulator is in the tank and regulates the fuel pressure by the amount of fuel it allows to flow back into the tank.

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    Moderator Cutlass's Avatar
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    Here's a picture of the T fitting I pulled off the internet. Ignore the yellow arrow.


    If you can't pressurize the return line then it sounds like the fuel pressure regulator is shot

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    Member joedude02's Avatar
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    Victory Red
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    an update on the situation. i've installed a new fuel pressure regulator and i still get the same problem. so, i've decided to throw another part at it. i've got an aeromotive fuel pump w/ wiring harness upgrade on order right now. i at least hope that a new pump will solve this issue. i had some "old" school mechanics say that it sounds like a vapor lock situation. i find it hard to believe, but i do have 3" true dual exhaust and that pipe is about 4 or 5" away from the lines. i dont think its close enough to cause any heat transfer in that extreme degree. anymore thoughts on this?

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    Senior Member JayTA98's Avatar
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    sounds like they are far apart to me but i never had the vapor lock issue with any of my cars.

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