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Thread: ?Normal deflection? of air flow sensor

  1. #1
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    Join Date:  Nov 2012

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    ?Normal deflection? of air flow sensor

    Im doing the dmc technical ?engine wont start? flowchart c1 / c2.
    Does anyone have a video of normal deflection? How much does your air flow plate move during cranking ?
    Mines moving a bit. Whats the difference between minimal deflection and normal deflection?

  2. #2
    Senior Member Rich's Avatar
    Join Date:  May 2011

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    Good that you're using the factory chart.

    No video. But I can describe it.

    Ran the test on my unmodified PRV today. This engine starts instantly, runs/idles great. I've observed this cranking test on it in the past. It has a Rhone-Poulenc (OE) starter. Inertia switch turned off in order to prevent starting during test. 1 year old battery, full charge. Viewed the back of the air flow plate, the edge closest to the fuel distributor.

    Normal deflection: The back of the air flow plate moves up and down in a pulsing motion during fast/normal cranking. Each cylinder-fill moment moves the plate ~2mm down, followed by closing somewhat for a moment until next cylinder fills with air and it moves back to ~2mm opening. When cranking stops the air flow plate immediately moves to the up position.

    Minimal deflection: Probably <2mm max movement or no movement at all.
    March '81, 5-speed, black interior

  3. #3
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    Feel for some pressure when you push on the air sensor plate, that will tell you if you have fuel pressure. You should also hear the fuel pump. If you can confirm fuel then you have to check spark. One of the most common reasons to not have spark is a bad/dirty connection on the white ballast resistor. Remove and replace the connectors on it and try again.
    David Teitelbaum

  4. #4
    Senior Member Rich's Avatar
    Join Date:  May 2011

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    Now there is a video of the test described in post #2

    The dial caliper behind the metering plate shows mm/cm scale on its left for reference
    Last edited by Rich; 06-13-2024 at 10:07 PM.
    March '81, 5-speed, black interior

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