fuel gauge sending unit, need output data, have strange readings Options

[SirAndy]

does someone have the exact numbers handy of what the fuel sending unit SHOULD put out? min/max voltage etc. (IMG:style_emoticons/default/confused24.gif)

i have about 4 gallons in the tank and the fuel light still comes on,
BUT i get only about 5.5 volt on it, so it's dim !?! isn't that supposed
to be more like a on/off switch thing and not a dim in/out light?
also, if i remove the bulb and measure directly, i get 12V !!!
and it's not the bulb. exchanged (known good) bulbs and get the same.
looks like it's going down to 5.5 V when under load! WTF!!!! (IMG:style_emoticons/default/blink.gif)

also, my fuel gauge doesn't do anything. first round of measuring showed 0.5 V,
then 10 minutes later it shows -0.1 V ????? (IMG:style_emoticons/default/wacko.gif)

soooo, anyone who has a manual handy?
thanks,
Andy

[MarkV]

Isn't the sender more like an ohm meter? It should just measure resistance? (IMG:style_emoticons/default/confused24.gif)

[SirAndy]

Isn't the sender more like an ohm meter? It should just measure resistance? (IMG:style_emoticons/default/confused24.gif)

yes. but i still should get something on the wire (volt-wise).
if i put 12V directly on the gauge, i get a full tank (IMG:style_emoticons/default/cool.gif)

and the gas-light is not supposed to be dimmed down to 5.5 V either ....

the way it works, the more gas in the tank, the more V on the wire, less gas, less V.

but i need to know the exact numbers i have to look for ...
Andy

[MarkV]

I looked in the Haynes manual but it is worthless. Haynes says to check that you have a good ground & check that you have fuel in the tank.

On a car w/ no light there is just one wire to the sender. The sender is a variable resistor to ground. Most cars dont have 12v going to the tank.

Try measuring the gage/sender w/ ohms & not volts???

[914Timo]

Hard to say about volts, but the resistanse should be 0 ohm when the tank is full. When the tank is empty it should be about 80 ohms or between 60 and 90 ohms in any case.

The gas-light switch is on/off.

I think you have some faulty connection there.... (IMG:style_emoticons/default/confused24.gif)

Hope this helps.

[SirAndy]

I think you have some faulty connection there.... (IMG:style_emoticons/default/confused24.gif)

yepp. pretty sure of that.

thanks for the ohms. will check tomorrow ...
Andy

[Brad Roberts]

Do you have the wires flipped ?? The dim light might have the wire on it for the "gauge".

B

[SirAndy]

Do you have the wires flipped ?? The dim light might have the wire on it for the "gauge".

thought about that too. the 5.5V i'm getting on the light could be for about 4 gallons of gas (IMG:style_emoticons/default/rolleyes.gif)

the wires on the gauge are correct, but i may have mixed them up in the front when i put the tank back in.

Andy

[Dave_Darling]

I'm pretty sure you did.

The sender for the light is just a metal plate on the bottom of the float in the tank. The plate "lands" on two metal contacts when the float is low enough, which lets the current flow through the light.

The sender for the gauge is a set of "resistance wire", and the float has one contact on it that slides along the wire. When the float is closer to the bottom of the tank, there is more resistance wire in the circuit path and therefore more resistance to the sender. The gauge reads less fuel with higher resistance.

--DD

[Dave_Darling]

Ah, found the note. I wrote down "32 ohms == E". My sender apparently has 32 ohms of resistance when the tank is empty. And, of course, lower when full. I think I remember about 11 ohms?

--DD