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Thread: New fuel pump

  1. #1
    Senior Member
    Join Date:  May 2011

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    New fuel pump

    Hi all.. I just replaced my fuel pump and did the spring in the hose etc.. the tank is clean. the filter in the tank is clean. boot and cover are newer and perfect. car runs and drives great but is now having a hot start problem after sitting for an hour or two.. it took me a min or two of cranking to get it to start.. but only after sitting for the hour or so.. if I drive it and shut it off it starts right back up.. any thoughts?? the accumulator is probably 10 yrs old.. but it never had this problem with the old fuel pump.. thanks guys.. ps I have a fuel pressure tester that I was going to hook up this weekend to check pressures..

  2. #2
    Senior Member Parzival's Avatar
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    Sounds like you're losing rest pressure faster then the car can cool down enough to activate that cold start valve. I would recheck all of your connections. you may have a loose hose clamp that is allowing the pressure to slowly drop.

  3. #3
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    losing rest pressure..

    so you think a clamp is loose on the fuel pump?? I am positive they are not... and the car did not cool off when I got home. I just shut it off after driving for a bit and it fires right up any time.. just doesn't after an hour or so of sitting now....

  4. #4
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    okay

    its been a half hour.. I just went out and cheked the metering plate and it still has pressure.. I pushed it down a few times and has decent pressure still.. but wouldn't start .. it just cranked and cranked for a few seconds.. tried that a few times then it fires right up... any thoughts...?? lol

  5. #5
    Senior Member Parzival's Avatar
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    Quote Originally Posted by painterdave72 View Post
    so you think a clamp is loose on the fuel pump?? I am positive they are not... and the car did not cool off when I got home. I just shut it off after driving for a bit and it fires right up any time.. just doesn't after an hour or so of sitting now....
    well, if its losing rest pressure slowly, then yeah, It will start right back up if you just shut it off.(not enough time to lose pressure)
    now, give it an hour and You may have lost that pressure, and the engine might not be cool enough yet for the cold start valve to be activated by the thermo time switch in the water pump.
    I think if everything is tight and the accumulator is in good shape, you should hold rest pressure for 2 hours. If you have Bitsyncmasters RPM relay, I think you get 3 hours because it re-primes the fuel pump at shutdown (I believe this is how his relay works).
    for some reason or another it sounds like its not maintaining the pressure long enough (I.E. after one hour your car does not start) but will start cold (cold start valve assisting startup) and will start right after shut down(not enough time off to lose pressure)
    So unless your accumulator just decided to go bad at the same time you changed your pump, or you have a bad check valve at the new pump, or something is loose. The pressure is getting out some how.

    Did you also change your fuel filter?

    Try priming you fuel pump several times before attempting to start it. You can do this by turning the key to the first position for a few seconds and then back to off, and repeat a few times. Then try to start it and see if it starts up faster. When I changed all my fuel injector lines mine was not as eager to start up as it was. This only lasted a short time tho. perhaps there's just some air in the system still that needs to be worked out? that's a complete guess but maybe.
    Last edited by Parzival; 05-03-2019 at 11:04 PM.

  6. #6
    Senior Member Bitsyncmaster's Avatar
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    I know the specification for holding rest pressure is just a 40 PSI test after 10 or 15 mins after shutdown. But I found the real test is how long it holds any rest pressure in terms of hours. My car would have a warm start issue if I tried to start it between 3.0 to 3.5 hours on a hot summer day parked in the sun on blacktop.

    It just so happened my car would only hold rest pressure for 2.5 hours. So I made the my RPM relay extend rest pressure for another three hours by priming the fuel system (run pump for 0.5 seconds) at each hour interval after shutdown. So you need to hold rest pressure for at least one hour for my RPM relay to extend another three hours.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  7. #7
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    maybe

    its the check valve that came on the new pump not working?? I still have the one from the old pump I can try swapping them out....

  8. #8
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    and what i was saying last night

    was that the car still had rest pressure after sitting for a half hour but took a few tries to start also for some reason..

  9. #9
    Senior Member DMC-81's Avatar
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    Did the new pump come with an external check valve? Pics would be great.

    Yes, I would try swapping them out as a test.
    Dana

    1981 DeLorean DMC-12 (5 Speed, Gas Flap, Black Interior, Windshield Antenna, Dark Gray)
    Restored as "mostly correct, but with flaws corrected". Pictures and comments of my restoration are in the albums section on my profile.
    2006 Dodge Magnum R/T (D/D)
    2010 Camaro SS (Transformers Edition)

  10. #10
    Delorean Guru
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    One easy way to confirm a problem with rest pressure is to do the plug swap. If that gets it going then it is going to be the accumulator, the check valve, or the PPR unless you have a fuel leak and you would see and smell that.
    David Teitelbaum

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