Fuel Gauge Problems

[trodzen]

I need help with a fuel gauge problem..

When the Key is OFF the gauge shows empty
When the key is ON the gauge shows full

When checking the wires at the tank I find..
RED on top of the sender
BLACK attached next to it and grounded with the metal tank

Red and Black with the key on shows 6.5volts
Red and Black with the key off shows 0volts
Red to Black with the key off shows 0.08 ohms resistance

Strange but also, with the red disconnected I find 12 volts Red to Black.

Any help? What should the ohms be at full or at empty? Should I just figure out how to pull the sender from the tank to check that part out? or could it be in the gauge?

[Rockter]

Trodzen...

I suspect you have too high a resistance somewhere. I would expect more than 12 V at the terminals, with no load. Take off the red and black leads, switch on the key and see if you could run a wee load there, say a 12V bulb or something. The classic symptom of corroded connections is that the multimeter will read close to 12 V, but the lines will not draw a load as a corroded connection chokes off the current supply.

If it chokes off, check for corrosion in the supply wires.

I've ben there with that one a few times.

[timangiel]

I think the float in the tank(sending unit) may be stuck in the full position. If you can pull it out you should be able to check it. I really doubt it is the gauge since it does go from empty to full.

12v on the leads when diconnected does not sound strange to me at all, if you have a 12 v system and open the circuit you read source voltage if there is continuity back to the source because if there is no current flowing there is no voltage drop.

When you connect the leads to the sender you complete a circuit and the source voltage is divided between the gauge and the sender which are in series.

Trying to connect a lamp where your sending unit is probably will not be of much help.

If you get the sending unit out of the tank and diconnected, you should see the resistance of it change as the float is raised and lowered. Let us know how you make out. I pulled mine out once and it was pretty easy.

[Faster]

I think Tim's on the mark. Your numbers appear to indicate a stuck float - though the .08 ohms seems a bit low - but you can't be sure you are measuring only across the element unless you disconnect it first.

[trodzen]

thanks for the replies. Thanks Tim. I will pull the sending unit tomorrow. It wouldn't be difficult if it was out on deck but stuffed under a board and around the corner under the settee I'll be hanging upside down just to get to it.

Is there a normal resistance (ohms) that I should get at full or empty?

Todd
s/v Hestia

[sailingdog]

Todd-

The resistance the unit will give at full or empty really depends on the unit itself...there was no standard range for sender units—different manufacturers used different methods.

[donradclife]

There is a list of some of the standard resistances at this site

http://www.egauges.com/vdo_mult.asp?...ustrial_Chrome

[trodzen]

Update:

I have the sender in my hand. I have the gauge housing apart.

The sender with no attachments reads 25ohms at hi thru 260ohms at lo. I assume these readings are good? The sender is good?

The gauge has positive (I), Negative center bolt, and Sender (S) wire. As well as light positive wire. I placed a jumper on the gauge from neg to S with the tank sender wire removed. The guage goes from Empty to Full. This tells me the gauge is good?

Next I placed a jumper from the sender base plate to the gauge negative (with the negative wire on the gauge too) and a jumper wire from the sender center bolt to the gauge sender (with the tank sender wire removed.) The gauge alway goes to full.

When the sender is in the lo position the gauge goes to full. When the sender in the hi position, I notice the gauge goes well beyond the full mark.

Any ideas?
Todd

ps. ignore my ohms reading on my first post. my tester was not working correctly.

[teshannon]

Time to think about switching to a Tank Tender. No moving parts or electical connections.

[sailingdog]

LOL... a bit drastic and kind of pricey.

Originally Posted by teshannon

Time to think about switching to a Tank Tender. No moving parts or electical connections.