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Thread: Fuel Pressure Loss

  1. #1

    Default Fuel Pressure Loss

    I'm at a loss here. Last year I bought the 15x3 HydraMat to overcome fuel starvation below 1/2 tank. I have two Walbro 400 LPH pumps that run one at a time. Installed the HydraMat on one pump only to see if it would help. It worked great. So this year I decided to install another HydraMat on the other pump. Now it starts, idles & cruises the way it did before installing the second HydraMat. However, now when I step on it fuel pressure goes from normal to single digit. I have pulled the pump assembly several times checking position of HydraMat, hoses & wiring. I have 13+ volts at pump. I re-installed the OEM sock back on one pump. Both pumps do same thing when I switch between them. Each pump has a check valve installed inline outside the tank on the suggestion of the company I bought tank from, because of the starvation problem I had prior to installing HydraMat. They thought possibly fuel was returning back through off pump. I didn't think that would happen because I thought the pumps had a check valve. I tell you about the check valves because wondering if something could have happened to check valves when system was open for one week? I'm going to remove one check valve to see what happen. At this point I really don't know what to do, any help? Ideas would be greatly appreciated.

  2. #2
    Join Date
    May 2014
    Bostwick, GA


    Tank well vented? Take the checks out of both lines, run both pumps at the same time. Running both will disallow backfeed. What happens?
    Injector Inspector
    USAF 1960-1964
    Drag racing since 1955

  3. #3


    Thanks for replying Chuck. I pulled the 100 GPH fuel filter out to look at it. Last year I had foam around pump assembly. I pulled it out when I installed first HydraMat. So the filter element was black, it didn't really looked clogged. I replaced it with 175 GPH filter that uses 8 AN fittings that match my 8AN supply line.

    I wasn't happy with the way the terminal ends fit the spades on the pumps, they just didn't seem tight enough. So I soldered terminal to pump spades. Rechecked fuel pressure, lowered it from 45 to 43. Now only one pump is working. Didn't matter right now, just wanted to take it out see if fixed. Runs great, I will dig into other pump tomorrow, thinking maybe I created an open when I soldered spades. Thanks again.

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