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Thread: LNF Cobalt SS Low Side Fuel Pressure?

  1. #1
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    LNF Cobalt SS Low Side Fuel Pressure?

    Hello,

    Does anyone know what the low side fuel pressure should be on the LNF Cobalt SS?

    I had a customer texting me telling me that he got a Low Rail Pressure code right after doing a in tank fuel pump upgrade. He installed the AEM E85 compatible 320lph fuel pump.

    He does have ZZP cam with upgraded fuel lobe and the Opel injectors.

    But he states that he has not even got into boost since doing the in tank fuel pump upgrade and then got this code. So I asked him to check the low side fuel pressure, so waiting to hear back what he says it is. But I honestly never myself have checked fuel pressure on the low side of the LNF's to see what it even is.

    Looking for key on engine off pressure readout.

    Thank you,

  2. #2
    Senior Tuner cobaltssoverbooster's Avatar
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    KOEO 57-60 psi average....
    2000 Ford Mustang - Top Sportsman

  3. #3
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    Thank you very much, that is what I would have guessed it would have been. Just wanted to have someone confirm.

    Thank you,

  4. #4
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    So the customer brought his car by my shop this last Saturday. He was unable to find a fuel pressure gauge that he could use to check fuel pressure, so I checked it for him.

    I got 70psi with key on, engine off.

    And then constant bouncing needle from 50psi to 80psi with key on, engine on.

    So I started to do some tuning for him while he was there, as I was unsure if that was normal condition on the LNF as the high pressure fuel pump is so close to the service port (maybe causing that pulsation).

    His setup is AEM 320lph in tank pump, Opel Injectors, ZZP Stage 2 cams (larger fuel lobe) and running E47 mix fuel. Right around 24-25psi of boost around 5800-6000 rpms, high pressure fuel pressure would drop to 700psi and start going lean so I would have to let out. So I attached my fuel pressure gauge back up and wanted to see low pressure while the high pressure started to drop. And sure enough when the high pressure drops down to 700ish psi, the low pressure would drop down to 20-30psi.

    He is going to be pulling the tank back down to confirm everything is fine with the installation of the low side pump. He said he might go ahead and install a Walbro 455lph pump while he is there. But he asked if there is any other recommendation that he should do while he has the tank down again.

    Is the stock regulator the same style as the LSJ cars? If so, would it be a good idea to do a boost reference fuel pressure regulator like you do on the LSJ cars? If not, are the stock fuel pressure regulators good enough to leave alone?

    Thank you,

  5. #5
    Senior Tuner cobaltssoverbooster's Avatar
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    no the lnf style regulator is built into the tank pump assembly. you can pinch them down to increase pressure a tad.
    something may have dropped into the tank and it gets sucked up to the pump inlet which is rare so he wont know until he drops the tank again.
    if you do install an external regulation unit then it doesn't need to be boost referenced because it doesn't have to worry about delta pressure differences to any other system.
    the pressure supplied to the hpfp just needs to be constant; it doesn't need a referenced signal regulation system. stock is 60 psi and if your system can handle it then turn it up 8-10 psi more than stock and leave it alone. the hpfp has an electric relief solenoid so overcooking the inlet pressure doesn't necessarily gain a whole lot of performance. the supply only needs to be constant.
    if your customer wants to upgrade then he can use the factory fuel pump wire to trigger a relay in which he can control a 10 gauge feed to the aftermarket pump. having pump wiring of size can prevent operation pressure drop on the higher flow side of the pump.
    otherwise there really isn't a whole lot to be done on the fuel side short of 5th or secondary rail injection.
    Last edited by cobaltssoverbooster; 10-02-2017 at 12:12 PM.
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  6. #6
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    if the canister is stock in the tank. it's sucking the canister dry at upper rpms.
    The most hated, make the most power.
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    Senior Tuner cobaltssoverbooster's Avatar
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    I cut the bottom off my canister and ran Holley hydromat to my aftermarket walboro so I wouldn't have inlet feed issues. Since I never had the problem myself this is new information for myself. I stopped hanging out on css and jbody a long time ago. I just stay here where the tuners go.

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    i ran into it on mine with a modded 255 on the tvs setup. band aided the tune around it. meh
    The most hated, make the most power.
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    Great information guys.

    Thank you,

  10. #10
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    Quote Originally Posted by cobaltssoverbooster View Post
    I cut the bottom off my canister and ran Holley hydromat to my aftermarket walboro so I wouldn't have inlet feed issues. Since I never had the problem myself this is new information for myself. I stopped hanging out on css and jbody a long time ago. I just stay here where the tuners go.
    I have a Cobalt and am about to install a AEM 320lph E85 ready pump and was wondering what hydromat model you used and what all you did to make it work with your walboro.

  11. #11
    Senior Tuner cobaltssoverbooster's Avatar
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    i cant remember what mat i used. i think it was an 11x11 or 15x15. they usually have a 1/2 npt bung on them so i ran a hose from the mat to the top of the pump housing and externally mounted the walboro.
    when you pull the pump just measure out a space in the tank where you want the mat to go and then purchase the largest mat to fit that area.
    if you go this route do not use any sealing tape or sealing paste on the hydamat threads. its literally thee fastest way to smoke your new fuel pump.
    2000 Ford Mustang - Top Sportsman