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Thread: Checking the Manifold Vacuum Pressure … 1958 L6-226

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    Checking the Manifold Vacuum Pressure … 1958 L6-226

    The “ Service Manual for Jeep Utility Vehicles” (Para C-18) states to test the Vacuum pressure to determine certain valve issues. 550 rpm with a goal of 18-21 in of mercury.

    Checking the vacuum can tell you a lot about the status of the Valves.

    OK, but this vehicles vacuum is generated by the mechanical Fuel Pump and not from the manifold. There doesn’t appear to be any manifold vacuum tap to check it with. E.g. the Carburetor vacuum line comes from the mechanical fuel pump. Not anything relating to the valves.

    So how do I test the the manifold pressure? What am I missing?

    Jake

    1958 Willys PU L6-226 VIN 55268-45757

  2. #2
    Super Moderator bmorgil's Avatar
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    Hello Jake, not quite. The vacuum for the windshield wiper is "assisted" by the fuel pump. All air throttled engines create vacuum. You test it at the port on the intake manifold, or the carb below the throttle blades if there is a port.
    Last edited by bmorgil; 04-05-2020 at 04:10 PM.

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    Quote Originally Posted by bmorgil View Post
    Hello Jake, not quite. The vacuum for the windshield wiper is "assisted" by the fuel pump. All air throttled engines create vacuum. You test it at the port on the intake manifold, or the carb below the throttle blades if there is a port.
    Thank you so much. You answer actually answer multiple issues for this project. Jake

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