LS1 - return versus returnless fuel system

Discussion in 'High Tech Retrofits' started by cdorhout, Mar 15, 2012.

  1. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

    Messages:
    19,245
    Likes Received:
    679
    Joined:
    Jun 1, 2005
    Location:
    Scott from Hamilton, NJ
    If I get time later I'll check the 99 FBody manual I have. But I think the FP is powered by a relay. No voltage control there. And the higher HP guys seem to do harness upgrades with better pumps in those cars.

    Check the auto zone website, they had wiring diagrams. I think you'll see a relay powering the 2000 SS f/p.
     
  2. JJFarmer

    JJFarmer Veteran Member

    Messages:
    2,447
    Likes Received:
    1
    Joined:
    Jun 28, 2002
    Location:
    Lenoir City, TN
    All the ecm does on a LS motor is either provide a ground to the fuel pump relay to power up the pump or remove the ground on the fuel pump relay dropping the 12 volts to the pump
     
  3. cdorhout

    cdorhout Veteran Member

    Messages:
    171
    Likes Received:
    0
    Joined:
    Jun 29, 2010
    Location:
    Des Moines, IA
    So in that case, return and returnless systems are the same at the fuel pump. The only difference is where the return is, either at the rail or at the fuel filter.

    So that tells me the tune can stay the same. Fuel pressure is always the same for both fuel systems.
     
  4. JJFarmer

    JJFarmer Veteran Member

    Messages:
    2,447
    Likes Received:
    1
    Joined:
    Jun 28, 2002
    Location:
    Lenoir City, TN
    GTO wiring....

    [​IMG]
     
  5. LSXZ28

    LSXZ28 Veteran Member

    Messages:
    552
    Likes Received:
    0
    Joined:
    Jul 17, 2009
    Location:
    Crofton, MD
    The PCM for an LS1 does not control the fuel pump speed - that is constant. And that is just a dampener on the F-body/vette/GTO rails.

    The issue comes into play with the injector tuning tables - if you use an in-tank pump/regulator assembly or the Corvette filter/regulator that was shown above, you can use the stock injector tables. If you put a vacuum referenced fuel pressure regulator up on the rails (by using aftermarket rails), you have to retune the injector tables.

    Basically, the tables for what GM considers "returnless" take into account the changes in pressure that the injector will see by tuning the pressure vs. kpa. If the fuel rail pressure is NOT referenced to manifold pressure, then decreasing the manifold pressure has the same effect as increasing the fuel rail pressure. The fuel flow rate of the injectors will increase at higher manifold vacuums (i.e. lower manifold pressure).


    If you look at the GM truck tunes, they have flat injector tables because GM uses a return style fuel system (and the FPR is vacuum referenced) on the trucks...

    Here are pics of the tables - first one is the Camaro, second one is the truck

    [​IMG]

    [​IMG]

    Hope that helps!
     
    Last edited: Mar 15, 2012
  6. Leonards78LT

    Leonards78LT Veteran Member Lifetime Gold Member

    Messages:
    1,031
    Likes Received:
    0
    Joined:
    Jan 21, 2001
    Location:
    Central Oklahoma
    ^^^^^^ Bingo! A good explaination, with pictures.
     
  7. cdorhout

    cdorhout Veteran Member

    Messages:
    171
    Likes Received:
    0
    Joined:
    Jun 29, 2010
    Location:
    Des Moines, IA
    Yes, that is perfect and exactly what I was after.

    Thanks for all the help guys. Now I know when I have my VATS, AIR, and EGR disable to also convert the fuel maps to look more like the truck tune. I'll ask my tuner about this.

    Thanks again, everybody.
     
  8. andrew69_04

    andrew69_04 Veteran Member

    Messages:
    254
    Likes Received:
    0
    Joined:
    Jan 8, 2012
    Location:
    Berthoud CO
    The ls ECM provides grounds for all relays (fans, a/c, etc) except for the fuel pump. It actually provides the 12v power for the relay.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.