Impreza Saddle Tank operation? No jet pump?

Discussion in 'Subaru Impreza' started by Petersch, Jan 24, 2023 at 11:22 PM.

  1. Petersch

    Petersch

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    I'm troubleshooting a fuel problem with my 2016 Impreza, but I can't get a good description on how the saddle tank fuel moves from the side of the tank without a fuel pump to the side with a fuel pump. If you don't know, the Subaru tank has a big hump in the middle for the drive shaft, so fuel can get trapped on one side of the hump. In most Subarus this is done with a suction pump, sometimes called a jet pump. The tank for 2016 has no jet pump, according to all the parts illustrations I have seen.
    Does anyone know how the fuel is moved over without a jet pump? The engine seems to be starving for fuel when the fuel gauge gets below 1/4. I use alldatapro for my technical manual, but they are very lacking in operational descriptions.
     
    Petersch, Jan 24, 2023 at 11:22 PM
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  2. Petersch

    Ecmbuster

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    What model? Are any faults recorded within the network?
    2016 Impreza - ??
    Pages 6 and 7 (Item 4)

    Check both level sensors (variable resistor) with a meter, using the Ohms setting.
    Save the values from full to empty. The resistance sweep should be clean and stable.
    The instrument panel should calculate both level sensors to offer "a close enough level reading".
    Read the TSB as well.
     

    Attached Files:

    Last edited: Jan 25, 2023 at 12:06 AM
    Ecmbuster, Jan 24, 2023 at 11:41 PM
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  3. Petersch

    Petersch

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    Impreza hatch back, maybe called a wagon. I know the quantity indication is accurate based on the refilling quantity when I top off at the gas station. That is, it's not empty when it shows 1/4, for sure.
     
    Petersch, Jan 25, 2023 at 12:33 AM
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  4. Petersch

    Petersch

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    Thanks for the attachment, but it is a fuel supply problem, not a quantity indication, for sure. I need to know how the engine can starve for fuel when there is clearly fuel in the tank. This is usually because the jet pump isn't picking up, but there is no jet pump in this model. Stumped....
     
    Petersch, Jan 25, 2023 at 12:41 AM
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  5. Petersch

    Ecmbuster

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    Look at the attachment, the "jet pump" is in the supply line. The term is incorrect, the main pump pulls fuel from the other side, through that line. The correct term is the Venturi effect.
    Check that line. Look for a restriction, damage or debris.
    Now measure main fuel pressure and fuel flow from main line to the engine injector rail.
    The measurement is taken at the fuel injector rail.

    https://www.underhoodservice.com/saddle-style-fuel-tanks/

    If the fuel level sensors have failed, blame poor quality fuel with too much ethanol damaging the resistors.
     
    Last edited: Jan 25, 2023 at 3:18 AM
    Ecmbuster, Jan 25, 2023 at 2:44 AM
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