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erratic fuel pressure

This is a discussion on erratic fuel pressure within the External Engine forums, part of the LSx Technical Help Section category; I have recently replaced my stock fuel pump with a granatteli 255lph pump. I also put in a new fuel ...

  1. #1
    never enough ponyslayer's Avatar
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    low fuel pressure

    I have recently replaced my stock fuel pump with a granatteli 255lph pump. I also put in a new fuel regulator while I had the tank down and added a new fuel filter. When I put a pressure guage on and turn the engine to on the FP goes to about 50 psi for a second then drops to zero (while the key is still in the on position). I checked the FP with the engine runing and it sits at 50 psi. When I revved the engine the pressuer actually droped a pound or two.
    The FP on my car should be 58+.
    Has anyone else had this problem? Anybody have any suggestions to why its doing this.
    Last edited by ponyslayer; 10-15-2010 at 04:58 PM.

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    cant remember what its called but sounds like you may have a small hole on the line inside the tank..... to/from the fuel pump. Just a guess.

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    never enough ponyslayer's Avatar
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    Quote Originally Posted by brp57 View Post
    cant remember what its called but sounds like you may have a small hole on the line inside the tank..... to/from the fuel pump. Just a guess.
    I think if it did there would'nt be a constant pressure on the line.

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    Quote Originally Posted by ponyslayer View Post
    I think if it did there would'nt be a constant pressure on the line.
    You don't have constant pressure. However, a leak inside the tank line could explain what's happening. I've had similar conditions working with high pressure hydraulic pumps that usually ended up being an internal leak in the tank, fuel shouldn't be that much different.

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    never enough ponyslayer's Avatar
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    Yeah the more I think about it the more it sounds probable. I'll drop the tank soon and look for any leaks.

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    Check the relay under the hood before you drop the tank.

    Also, I would highly suggest cutting a "door" into your hatch area right above the fuel pump. It's a lot easier than constantly dropping the tank.


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    never enough ponyslayer's Avatar
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    Quote Originally Posted by ls1camino View Post
    Check the relay under the hood before you drop the tank.

    Also, I would highly suggest cutting a "door" into your hatch area right above the fuel pump. It's a lot easier than constantly dropping the tank.

    Click for full size
    dont you have to drop it to cut the door out and what do you use to open and close/seal it?

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    never enough ponyslayer's Avatar
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    bump...

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    Quote Originally Posted by ponyslayer View Post
    dont you have to drop it to cut the door out and what do you use to open and close/seal it?
    No, just be careful when cutting with a Dremel.

    I JBWelded a door hinge and slide lock onto the panel/body, so now it opens and closes fine. I also got some weatherstripping for around the edge, which seals it when closed.

    I'll post up a pic if you'd like when I get home.

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    does sound like you have a leak in the tank or that FPR isn't right.....

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    never enough ponyslayer's Avatar
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    Quote Originally Posted by ls1camino View Post
    No, just be careful when cutting with a Dremel.

    I JBWelded a door hinge and slide lock onto the panel/body, so now it opens and closes fine. I also got some weatherstripping for around the edge, which seals it when closed.

    I'll post up a pic if you'd like when I get home.
    Yeah, that would be great!

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    The Demon Demon_Z28's Avatar
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    When I upgrade my fuel pump, an access hatch will be made. But I would say there is a check valve that could be stuck open that will cause fuel pressure to drop and return to the tank, a pin hole leak in the fuel line inside the tank will definitely cause low fuel pressure.

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    never enough ponyslayer's Avatar
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    Quote Originally Posted by Demon_Z28 View Post
    When I upgrade my fuel pump, an access hatch will be made. But I would say there is a check valve that could be stuck open that will cause fuel pressure to drop and return to the tank, a pin hole leak in the fuel line inside the tank will definitely cause low fuel pressure.
    I have done the egr/air delete on my car when I Installed the race style LT header with no air provision but I havent deleted it out of the computer yet... Not sure if that adds another scenario to low FP.

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    The Demon Demon_Z28's Avatar
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    Quote Originally Posted by ponyslayer View Post
    I have done the egr/air delete on my car when I Installed the race style LT header with no air provision but I havent deleted it out of the computer yet... Not sure if that adds another scenario to low FP.

    Your AIR system is for pumping air through the manifolds to warm up the cats faster. Your EGR system returns exhaust gases from your manifolds into the intake to burn unused gas and hydrocarbons.(Both of these for for Emissions) Neither of these will Effect fuel pressure whether the PCM throws a code for them or not. It won't effect drive-ability either. The Fuel system is Stand Alone to the exhaust system. They do no work together as a complete system. Hope this helps.

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    never enough ponyslayer's Avatar
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    where is the check valve you're refering to?

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