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Fuel Gauge on FPR Drops 5lbs when Vac Off
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Thread: Fuel Gauge on FPR Drops 5lbs when Vac Off

  1. #1
    Junior SCH Member ebx's Avatar
    Join Date
    Jun 2010

    Question Fuel Gauge on FPR Drops 5lbs when Vac Off

    Hello All,

    I put a new fuel pressure gauge on the the fuel pressure regulator. There was a little plug on the FPR, that is where I put the gauge. I was very careful not to get any thread sealant on the end of the gauge threads so as not to plug up the little hole.

    At idle w/ the vac hose on it read 29 lbs. When I shut the car off, remove the vac line off the FPR and plug the vac line, then start the car, the fuel pressure gauge reads 24 lbs.

    I thought when the vac line is removed and plugged the pressure should go up.

    I turned the adj. screw two full turns clockwise and the pressure stayed the same.

    No fuel coming out the vac line nipple.

    I ran the car and my wide band O2 went from around 17 at wot to around 15. Right direction.

    So back at the house I turned the adj. screw one more full turn clockwise. Took the car out and 200' down the road my fuel line fitting at the fuel rail tube popped off and shot fuel everywhere. The car shut down. The fuel line is an aluminum Russell O spring type that fits over the factory style flared tube. The round spring was pretty loose inside the fitting, not tight.

    I couldn't push the fitting back on by hand so I used a socket and hammer and tapped it back on the tube. I adjusted the FPR screw counter clockwise three full turns back to where it was when I started. It started with no leak at fuel connection. I slowly got is back in the garage.

    Does anyone have any ideas why the fuel gauge didn't go up instead of down when the vac line was removed?


    Could I have basically closed the valve in the FPR to have popped the fuel line fitting?

    The whole reason for the gauge and FPR adjustment is to get my wide band o2 #s lower to around 11 at wot.

    Thanks for any ideas.
    Powerdyne (6 Lbs.) Cobra Upper & Lower (P&P, Extrude Honed), SVO Aluminum X-302 SVO Heads (P&P), Forged Pistons, 306 Block, 65mm TB, 75mm Mass Air, 12" Cone K&N, 4" Inlet Tube, 30 lbs. Inj., 255 Pump, MSD Blaster Coil, MSD 6BTM, Electric Fan, BBK 1 5/8" Shorties, , X-Pipe, Cat Back, 3:55's, Stock ECM, Etc.

  2. #2
    Junior SCH Member
    Join Date
    Oct 2012
    Weird proble with the fpr maybe it's faulty

    If u r trying to get it to run richer u going to have to
    Crank the pressure cause the computer will adjust for about 10-15percent so adjusting that much higher will prolly mess up ur drivability since ECM Will be pegged on the adjustment side ur best bet is to tune in some more fuel adjusting the Maf transfer

  3. #3
    Senior SCH Member
    Join Date
    Apr 2006
    what you set the fpr at with the vac line off and plugged is where it will stay,unless under boost with the vacuum line hooked up.. if the vac line is on it will reference less fuel pressure at idle under full vacuum, when the engine is under load it will produce less vacuum and the fuel pressure should go up...

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