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LS1 - return versus returnless fuel system

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

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  1. Mar 15, 2012 #11
    BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    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. Mar 15, 2012 #12
    JJFarmer

    JJFarmer Veteran Member

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    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. Mar 15, 2012 #13
    cdorhout

    cdorhout Veteran Member

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    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. Mar 15, 2012 #14
    JJFarmer

    JJFarmer Veteran Member

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    GTO wiring....

    [​IMG]
     
  5. Mar 15, 2012 #15
    LSXZ28

    LSXZ28 Veteran Member

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    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. Mar 16, 2012 #16
    Leonards78LT

    Leonards78LT Veteran Member Lifetime Gold Member

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    ^^^^^^ Bingo! A good explaination, with pictures.
     
  7. Mar 16, 2012 #17
    cdorhout

    cdorhout Veteran Member

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    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. Mar 24, 2012 #18
    andrew69_04

    andrew69_04 Veteran Member

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    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.
     
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