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I've bought a 1988 Honda Accord (3rd gen) with an issue where the fuel gauge always reads full.

I removed the sender unit from the tank and cleaned it with some contact cleaner (it was kind of copper coloured). Before replacing it within the tank I tested it outside the tank connecting it to the car and moving the float by hand - the gauge worked fine and responded to me positioning the float.

So, I reinstalled the sender back into the tank. However, now that the sender is back in the tank the problem has returned - the fuel tank reads full again (tank isn't full) and won't drop when I turn the car off.

Would anyone know what could be causing this or have any other ideas?

Thanks

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    How are you grounding it when testing out of the tank? How does it ground when in the tank ?
    – Harper - Reinstate Monica
    Commented Sep 22, 2019 at 0:09

5 Answers 5

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I would bet there's an issue with the sensor grounding out when it's installed into the tank due to it staying pegged 100% of the time on the dash.

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  • Does it use the tank it's self to ground? The tank is very dusty around where the sensor is plugged into.
    – MeltingDog
    Commented Sep 21, 2019 at 23:39
  • @MeltingDog if you dont see another ground, then yes--- wait a minute, how were you grounding it for testing outside the tank?
    – Harper - Reinstate Monica
    Commented Sep 22, 2019 at 0:10
  • @Harper I think this might have a ground outside the tank. There are 3 pins on the socket. When I tested I actually had it resting next to the tank on a drop sheet.
    – MeltingDog
    Commented Sep 22, 2019 at 4:16
  • @Harper never mind about my comment above. Seems to be it does use the tank. It's weird - there is paint where the contact to the tank should be...
    – MeltingDog
    Commented Sep 22, 2019 at 9:06
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Is there any way to check for physical obstruction? I'm wondering if if the float is getting caught on a baffle that's stopping it from moving through it's full range?

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  • Pretty much every sending unit I've installed (only a handful) had to be inserted from the top in the 'empty' position.
    – user16128
    Commented Sep 22, 2019 at 8:20
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I agree with the above. The most likely cause, is the tank not being grounded if the sender only has one cable. The tank may be installed with soft pads between mountings and chassis, so should have a grounding lead somewhere. If the tank relies on the mounting bolts making the connection, they may not, with or without pads. The ground lead is often a second lead to the sender, so make sure it is grounded at the other end, especially if you didn't use it to test with the sender out of the tank.

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    Your answer really doesnt make sense to me. If this were a lack of ground issue (ie: relying on a ground which wasn't there), it would have the problem whether inside or outside of the tank.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 21, 2019 at 21:43
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Some tank / sender combinations rely on the clamping ring to also provide the ground connection.

We had one model of car that had so many issues with this (paint, corrosion) that we would solder an earth point to the sender and run a direct earth to the body.

Sorted those fine...

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  • Hmm I suspect this might be the case. I might try to test with aligator clips.
    – MeltingDog
    Commented Sep 22, 2019 at 9:04
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The fuel pump is connected in with the oil pressure warning light and the seat belt switch so that the fuel pump wont keep pumping gas when the Ignition is only in the ON position and the engine Isn’t running… so a diode had to added in on the low pressure side of the oil pressure switch to eliminate any feedback.

If the wiper and resistor the resistor give you an accurate stable reading even when you wiggle the wires then I'd check to make sure that their wasn't corrosion built up on the connector itself, and that there was no loose wires, not just on the fuel pump sending unit but on the harness towards the backside of the car that usually sits near the frame also.

The fuel gauge works by ohms of resistance, The higher the ohms the higher the gauge goes to full, the lower the ohms, the lower the gauge goes to empty, that's why other have said to check the ground connections, if a wire was grounded somewhere, that would give the Guage greater George Simon Ohms of resistance :D

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