zero fuel pressure after warmup

Discussion in 'Troubleshooting & Diagnosis' started by 69camaromaster, Nov 16, 2008.

  1. 69camaromaster

    69camaromaster New Member

    5
    0
    Jul 6, 2007
    yonkers, n.y.
    Hey Guys need help with something driving me nuts. I installed a Mallory 140 pump and bypass regulator w/ 1/2 inch supply and return lines sumped from the stock tank. Problem that I have is the gauge at the carb inlet starts at 8 psi dead cold and slowly drops to 0 psi after ten mins. warming up. first thought was vapor lock, so I insulated the lines wherever nesscessary and left off the gas cap. same thing. If I shut it off and let the pump run the pressure starts to build back up. However it takes just as long to build back up as it does when it initialy drops off when it's running. I checked all the filters and the inlet to the pump, all clean. Took out the reg. locknut and got 1 psi on the system with no restrictions. Also checked voltage too. The car starts up fine run strong for 15-20 mins, then start to loose a little power. Never stalls though luckly! I only loose pressure when it's running. Any ideas you guys can give me would help, cause I'm lost at this point! Thanks.
    P.S. the gauge at the regulator does the same thing as the one at the carb it just takes a little longer to drop off pressure. thanks again
     
  2. fridgeguy

    fridgeguy New Member

    Possibly the sock on the pick up?...Did you install a new pick up/sender. If not the sock could be plugged. Those little guages aren't the most accurate either but you do mention the engine loses power so than would lead to a delivery problem.
     
  3. Batman

    Batman Administrator Staff Member Lifetime Gold Member

    8,673
    6
    Dec 13, 1999
    Mission Viejo, CA, USA
    Sounds like there might also be a leak before the fuel pump and the pump is sucking air (ask me how I know about these things).
     
  4. 74 Z28 dude

    74 Z28 dude Veteran Member

    269
    0
    Mar 23, 2005
    North Bend, WA USA
    From what you have stated. Questions:
    What is the current draw on the pump when you first start it and again when you have lost pressure? What is the voltage drop on both the power feed side and ground side, before and after. If pump current draw goes down then either it is not facing the resistance of fuel to pump(plugged pick up?) or the pump is faulty. All that assumes it is capable of recieving the proper amount of current flow supplied with the engine running. 13-14 volts with little to no resistance on either the power or ground sides. Note that an ohm meter check of resistance is not a sufficient enough test of 'real world' conditions. Let us know.
     
  5. 69camaromaster

    69camaromaster New Member

    5
    0
    Jul 6, 2007
    yonkers, n.y.
    its a stock tank with a CE. sump welded to the tank. The supply and return are piped directly to the rear most part of the sump. Supply on the left, return on the right. I used thread compound on all the fittings and everything seems tight, no leaks. I have to recheck the relay for volt. drop.
     

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