Fuel pump voltage at ~7v when idling.

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  1. #1
    CelicaSupra.com Member Darrow's Avatar
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    Fuel pump voltage at ~7v when idling.

    83 w/ 6mge Fuel gauge stopped working so I checked fuel pump voltage and it is 6.8v while idling. I have not checked voltage while driving. Also, 5.7v when key is turned but engine not on. Seems to match up with half battery voltage (13.8v). I haven't messed with the wiring for the pump. I have a keyless entry system installed, forgot where that is powered from. Everything else seems ok. Gauge and pump have continuity with ground. Gas gauge was working last week.
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  3. #2
    CelicaSupra.com Member SupraFiend's Avatar
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    What does fuel pump voltage have to do with your gas guage? 2 separate circuits.
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  4. #3
    CelicaSupra.com Member Darrow's Avatar
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    Ya. Just an observation. Turns out it's a mute point. Had the wrong wire tapped to read the voltage. Fuel pump is fine. Still no fuel indication though.
    Wonder what is getting half battery voltage.
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  6. #4
    CelicaSupra.com Member Darrow's Avatar
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    A little update:
    Took out the sending unit and it failed the TSRM test for resistance at the different positions. I took off the cover and the copper windings were all green. I took a wire brush to gently clean them off and sanded the moving arm part. Got the resistance to match the TSRM values. Though when the float arm is jiggled the resistance will vary wildly and go into kilo ohm values. I think this may be part of the problem and why the guage was working when driving. It was making contact enough to get a reading. Anyway, I installed the sender and measured the resistance. Got 34.5 ohms which should read about half tank. Next is to trouble shoot the gauge.
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  7. #5
    CelicaSupra.com Member Darrow's Avatar
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    Just checked the gauge and it seems to pass the TSRM checks. Though I only did U-IG check and the deflection check with the ~3.4w light. I am officially at a loss of what to look for. If anyone is still reading this ideas are welcome.
    Hopefully when I drive it again it will come to life.
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  8. #6
    CelicaSupra.com Member SupraFiend's Avatar
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    Might want to try a different sender still, assuming you have proper continuity at the sender connector on the car chassis harness side. Check the condition of the wires from the spare tire well to the sender.
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  9. #7
    CelicaSupra.com Member Darrow's Avatar
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    I have proper continuity in all the wiring. The wiring looks good. No signs of cracking or corrosion at the connections. I will try a different sender. One of the few things I don't have a spare of on hand.
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  10. #8
    CelicaSupra.com Member SupraFiend's Avatar
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    Is the sender still returning the right resistance values? I just restored one of these this weekend and opened up the box the resistor is in. If that little silver arm that rubs on it bends away at all it will break continuity and stop working. The whole assembly seems a little susceptible to mechanical wear and failure over time.
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  11. #9
    CelicaSupra.com Member Darrow's Avatar
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    Resistance values are ok. The top out at ~65 ohm instead of the 100ohms specified. I a looking into getting it rebuilt.
    The door seam a bit prone to wear. Mine I can tweak the float arm to cause an open circuit.
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  12. #10
    Boosting Mod SilverMk2's Avatar
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    I've had pretty good luck just cleaning the contacts on the wiper

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