LS1 - return versus returnless fuel system

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

  1. cdorhout

    cdorhout Veteran Member

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    My LS1 that is going into my '71 is from a 2000 Camaro that had a returnless fuel system.

    My '71 will get a return system with the Spectra tank and Walbro pump.

    I think the factory returnless system controls the fuel pump with the ECU, and slows it down at idle. Since the fuel pump slows down and speeds up based on load, does the fuel pressure go up and down throughout the map? Or does the fuel pressure regulator keep the pressure at a constant 60psi despite the pump slowing down at idle.

    I'm concerned that once I convert my LS1 to a return style, and set my FPR at 60psi, that I may be flooding the cylinders with fuel at idle since it may not be used to 60psi at idle.

    I hope that wasn't too confusing, not sure I described it well.
     
  2. Leonards78LT

    Leonards78LT Veteran Member Lifetime Gold Member

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    If you are using a single fuel line that feeds the injector rail, it is considered a "returnless system" and will have sloping fuel flow rate values across the scale that varies with engine load. This fuel rail is indentified by no vacuum line. If the pcm is already set up for this, then don't change anything (stock engine).
    If you go with a return system, which is identified by a vacuum operated fuel pressure regulator and dual lines on the fuel rail, then the fuel pressure rate will be constant, regardless of engine load. The excess fuel is returned back to the tank.
     
  3. cdorhout

    cdorhout Veteran Member

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    So since the fuel pressure is different at different loads on returnless vs return, will I need to retune my whole ECU for the change to a return system?
     
  4. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    I thought 4th gens had a fuel pressure regulator on the fuel module. I did not think GM varied pump voltage in those cars. Don't they run like 45psi or so?

    GM went to a returnless system in those cars in 99 for a reason I suspect. I'm sure Jody will chime in but it seems guys running return lines in retrofits were running into overheated fuel causing issues.
     
  5. cdorhout

    cdorhout Veteran Member

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    there is a fuel pressure regulator on the fuel rail, so that's why I'm a little confused. There just isn't a return coming off the FPR like there is in a return system.
     
  6. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    on a 2000 I think that is a damper, not a FPR on the rails.
     
  7. cdorhout

    cdorhout Veteran Member

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    ah, ok. It sounds like I'll definately need to retune my fuel map to run correctly with a return style fuel system.

    I don't think the Spectra tanks can be made to run with a returnless style, right? Because the pump isn't smart enough to work with the ECU?
     
  8. camcojb

    camcojb Veteran Member Lifetime Gold Member

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    the factory systems were not literally returnless; they returned fuel, just not off the rail. I know those are called returnless, just trying to give a brief explanation of what it really was. The stock fuel filters on the late model Vettes had the bypass and regulator built in, and there was a return line from there back to the tank.

    With the factory ECM controlling your fuel pump I'd just use the Vette inline filter/regulator (AC Delco GF822), and bypass off that like the factory did. That seems to be a very popular way to go with the LS swaps.

    http://www.amazon.com/ACDelco-GF822-Fuel-Filter/dp/B000C9S33U

    [​IMG]
     
    Last edited: Mar 15, 2012
  9. BonzoHansen

    BonzoHansen Administrator Lifetime Gold Member

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    Yea, IIRC the 4th gen just had a t inline up the rail a bit that returned to the tank. No more than a few feet away.

    I didn't think 4th gen ECMs did anything with pump voltage. Am I wrong on that?
     
  10. cdorhout

    cdorhout Veteran Member

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    Yeah, and I guess that's all I need to now too, is whether or not fuel pump voltage is controlled by the ECU.

    I've been searching LS1tech as well.
     

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