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Losing prime

Discussion in '01-04 LB7' started by SFC Cobb, Mar 21, 2010.

  1. SFC Cobb

    SFC Cobb Jesus Freak

    May 15, 2008
    Hurst, TX
    Two days in a row now I started my truck, let it warm up then drove out. I got to the same spot and the engine dies. I initially thought it was the same thing I had happen that is caused by the chip. I turned the key off and tried to restart but this time it didn't restart.

    I got out and raised the hood but a cursory look showed no leaks. I decided to check the prime and pushed the pump and it went down real easy showing there was air in the system. I pumped it up until the pump was hard. It started right up. Yesterday the truck ran fine the rest of the day.

    The morning it restarted and I drove to church and was coming home. I stopped for fast food and was idling for a few minutes. The engine was loping like it did yesterday. I drove out and started over an overpass and the engine started slowing down. I got off the road after coasting a while and pumped up the pump again and started it and drove home about mile.

    Filters haven't been changed for about 10-12K miles. The temp dropped into the low to mid 30's yesterday and today after being in the 70's.

    I am wondering if there may be water one of the two filters (1 add on at the fuel tank) or that they just need to be changed.

    What else could be the issue? The loping makes me think that the fuel pressure regulator may be the problem.
  2. NVW

    NVW Well-Known Member

    May 5, 2008
    Castor, AB.
    I don't know much about the Duramax but it must be sucking air somewhere in the fuel lines or it's draining back to the tank.
  3. CtChevy427

    CtChevy427 Still Kicking.... Staff Member Lead Moderator

    Apr 14, 2008
    North Haven, CT
    Tim, I have read the the stock filter housing can crack causing it to lose prime. Also since you just had it worked on I would look everything over very carefully. You never know what you might find.....
  4. WarWagon

    WarWagon Well it hits on 7 of 8...

    Nov 15, 2009
    These trucks do not have a sock / screen in the tank. I removed some junk from the check valves by taking the primer apart on mine.
  5. Matt Bachand

    Matt Bachand Depends on the 6.5

    Jun 10, 2008
    Worcester, MA
    Thats a good thing, but I'd install a Racor ASAP on mine.
  6. Diesel Tech

    Diesel Tech Registered User

    May 8, 2008
    Change th efuel filter and make sure and check the two o-rings and inner seal when you replace it. I've seen plenty of them leak enough to let air in but not drip fuel out. Since the suction comes from the CP3 anything that let's air in when sitting will cause it to do what you've got going on. It due for a fuel filter anyways so I would start there and see if it solves it.
  7. dutch

    dutch New Member

    Oct 5, 2008
    west Texas
    Check the bleed screw. Have had to replace mine as it was loosing prime thru there. It was not leaking fuel out although it was damp looking around it.


    May 9, 2008
    The bleed screw and also the O-ring that seals up the fuel primer pump are 2 spots to check that are easy to see. I know my milage recently dropped way down and I found that the O-ring for the pump was leaking fuel out as I have a lift pump on mine.
  9. SFC Cobb

    SFC Cobb Jesus Freak

    May 15, 2008
    Hurst, TX
    I changed the filters and haven't had a problem since then. Thanks for the input.

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