Fuel Sending unit issue...

[BethnKevin]

I have noticed that the fuel gauge reads full all the time and does not change. I took some advice from here and replaced the sending unit with a moeller from Boaters World. On our Donzi there was a Green wire attached to the sending unit and a Black and Pink wire to the ground. All of the sending units I looked at only have two wires, one for the sending unit and one for ground. Also after I got it hooked up and turned the key on, there was a small click sound one time and then the gauge reads full. Is it possible that the unit is wired up incorrectly? It is an 89' Donzi Ragazza 25 with 350 5.7L OMC Cobra. Thank you all for any information you might have.

[Just Say N20]

See if this helps. No instructions with the sender? They should tell you how to wire it up.

[BethnKevin]

Thanks. The sending unit came with directions on the back of the box, but were not helpful. I will look behind my gauge panel and see if the gauge is wired correctly from the wire diagrams you sent. Do you think maybe the pink wire that is grounded with the black ground could have something to do with it?

[Ghost]

There's a long thread here (that you probably don't want to read) about how temp gauges work.

http://www.donzi.net/forums/showthread.php?t=56580

It may offer some ideas if you have nothing else.

But I think maybe the most relevant info is what people said about how to test a temperature gauge: momentarily touch the gauge's sender terminal to a ground wire. It tells the gauge the resistance across the sending unit is near zero, the max temperature condition, so the gauge pegs.

IF a FUEL GAUGE WORKS THE SAME WAY, with low resistance in the sender corresponding to a FULL reading, and IF your gauge is okay:

Having the gauge being pegged all the time sounds like for whatever reason it is measuring near-zero resistance between its terminal for the sending unit and ground. Whether that means that the gauge's sending unit terminal is incorrectly wired to ground, or if there is a short to ground somewhere in the sender's lead wiring.

EDIT: As for the fuel sender unit itself, I don't know if it matters which wire goes to the gauge and which goes to ground. With a temp sender, I understand it does not. I would expect the same with the fuel sender, because I suspect it works by creating a variable resistance.

Just an idea. I've never worked on one, just thinking about how I *suspect* it works. If it were mine, that's what I'd look at first. If anything blows up, please let me know so I can delete my post. :)

Mike

[twofiftyeight]

The green wire is just a bonding wire to ensure good continuity between the sender and the tank which would also have a green wire grounding it to the rest of the electrical system.

The first thing to do when troubleshooting is to check the sender itself with a multimeter. With everything disconnected, positive lead on pink and negative lead on black. It should read about 35 ohms with the float in the full position and 240 ohms empty. If that checks out ok I’d go up to the gauge and check the connections and make sure the sender post (one with pink wire) is not grounded out on the negative and none of the connections are loose or touching.

If that all checks out fine, get your meter and check the resistance between the negative post and sender post on the gauge with everything connected and key on. If the gauge is still reading full and your reading is nowhere near 35 ohms, your gauge is the problem.



Hope this helps

[RickR]

The pink wire shoud NOT be grounded. It should go to the sender wire pole on the sender. The BASE of the sender should be grounded.

[BethnKevin]

I have some time off the next two days and will give this a try. I will get back with everyone to let you know how it turns out. Thanks again..
Kevin