1984 300D fuel gauge - ideas anyone?

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szcz - 22 Sep 2006 22:00 GMT

My fuel gauge always reads empty, and the reserve light is on. Here is
what I have tried:
1. Filled tank
2. Removed and disassembled sending uint. All looks good: wires intact,
contacts good, float moves freely, everything is clean.
3. Swapped another fuel gauge into cluster. Same zero reading.

Is there any kind of control unit between the sender and the gauge? Am
I down to the only possibility being a wire issue? Any other ways to
check?

Thanks again for all the free advice

Michael

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Alasdair - 22 Sep 2006 22:16 GMT

>My fuel gauge always reads empty, and the reserve light is on. Here is
>what I have tried:
[quoted text clipped - 10 lines]
>
>Michael

I don't understand the logic myself but contributors to the forum on
the UK Mercedes Owners' Club suggests that using low quality petrol
can play havoc with the accuracy of the fuel gauge. It suggests
either putting a fuel cleaner in the tank or filling up with
top-of-the-range petrol and this should remove any unpleasant deposits
from the system.

The relevant forum is at:

http://forums.mercedesclub.org.uk/showthread.php?t=20921&highlight=fuel+gauge

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Alasdair.

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Karl - 23 Sep 2006 02:27 GMT

The needle and the light are on two seperate circuits.
If the light is on, the float is sitting on the bottom. The float has two contacts on the bottom of
it. It has to sit on the bottom to turn the light on.

Unscrew the float tube out of the tank. Plug it back in. Turn the key on. Turn the tube bottom up so
the float moves. Light should go out and the needle should move.

> My fuel gauge always reads empty, and the reserve light is on. Here is
> what I have tried:
[quoted text clipped - 10 lines]
>
> Michael

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szcz - 23 Sep 2006 02:36 GMT

> The needle and the light are on two seperate circuits.
> If the light is on, the float is sitting on the bottom. The float has two contacts on the bottom of
> it. It has to sit on the bottom to turn the light on.
>
> Unscrew the float tube out of the tank. Plug it back in. Turn the key on. Turn the tube bottom up so
> the float moves. Light should go out and the needle should move.

I did this when I had the sending unit out. When the float is on the
bottom the gauge shows full. When the float is in any other position
the gauge shows empty

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Tiger - 23 Sep 2006 15:06 GMT

That is obvious enough. The sender is bad.

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Roland Franzius - 23 Sep 2006 09:06 GMT

szcz schrieb:

> My fuel gauge always reads empty, and the reserve light is on. Here is
> what I have tried:
[quoted text clipped - 6 lines]
> I down to the only possibility being a wire issue? Any other ways to
> check?

Check the mass cable at the back of the odometer.

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Roland Franzius

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Ken - 23 Sep 2006 15:08 GMT

> My fuel gauge always reads empty, and the reserve light is on. Here is
> what I have tried:
[quoted text clipped - 10 lines]
>
> Michael

If my reasoning is correct, the float guage should operate like a
variable resistor. you should be able to hook up a multimeter and check
the guage's proper operation from that..K

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