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Fuel Sending Unit

Old 04-20-2023, 06:04 PM
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Default Fuel Sending Unit

Several years ago I had a new float style sending unit installed and ever since the fuel gauge worked in reverse. I tried switching the wires around at the tank but that did not work. I upgraded all of my gauges to Gaffrig and now wonder if I have to buy one of their sending units? I found one on their site that has a post for 12 volts along with the ground and signal. The existing one only has signal and ground. They also sell the float style sending units with the signal and ground. Is there a switch somewhere on the float style sending unit that makes it work in either direction? Thanks for your help.


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Old 04-20-2023, 07:49 PM
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No switch.
What does the gauge do if you disconnect the sender altogether? It should register full.
Is there a chance it is wired wrong?

https://www.sailmagazine.com/diy/tes...%20the%20gauge.


Also make sure you don't have a VDO sender. They are differant than a Livorsi
https://www.vdomarinegauges.com/vdok...hm-range-2009/

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Old 04-21-2023, 12:39 AM
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Nearly all of the fuel senders and gauges are 240-33 ohm.
My old boat for some reason had a VDO oil psi sender and the gauge operated in reverse.

BTW, all of those senders are made by Centroid and can be ordered direct for about 1/2 of listed prices. CENTROID PRODUCTS - Electronic Fuel and Water Senders
The senders with the adjustable screws for E & F are no longer really made. They now come "pre calibrated" and they suck compared to my old adjustable ones.
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Old 04-21-2023, 06:07 AM
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Yup, there are two different ohm range style’s from E to F. Most all guages, then VDO. Damn Germans
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Old 04-21-2023, 09:02 AM
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I'm going to check your suggestions out because I need to know however it seems quite clear that I need a new sending unit. Can you tell if this is the "VDO" style or not by the pic?

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Old 04-21-2023, 09:25 AM
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You should be able to take that sending unit out and test it with an Ohm meter very easily to verify operation......id guess its more on the dash side but who knows....i did find this install guide for those sending units.....trouble shooting at the bottom
installation guide
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Old 04-21-2023, 11:51 AM
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Originally Posted by Wally
You should be able to take that sending unit out and test it with an Ohm meter very easily to verify operation......id guess its more on the dash side but who knows....i did find this install guide for those sending units.....trouble shooting at the bottom
installation guide
I redid the ground connection at the tank with a new fitting and used solder instead of crimping. I also did the same for the connection at the sending unit. It is very possible that I have a problem at the dash because I redid EVERYTHING however, I verified that the wires I have connected to my gauge line up with the ones at the sending unit. I removed the sending unit and put a meter on it. When in the empty position the ohm's are approx. 38 and in the full position it's about 250. Close enough. I hooked it back up without mounting it and it just flat out works in reverse. The fuel gauge is moving appropriately however in reverse. Like I mentioned before, it did the same thing with the old Faria gauge that came with the boat. Is this the VDO sending unit?

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Old 04-21-2023, 12:14 PM
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Hard to tell from the pic but maybe you can take that sending unit apart and flip the sensor 180 in the bracket???
I'd still double check the dash connections too...
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Old 04-21-2023, 02:37 PM
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I cant seem to find any instructions on Gaffrig's web page but the first thing you need to know is how the gauge is set up to work ? Are you sure you don't need to just swap the wires on the gauge ? Do you have a picture of the back side of your gauge ?
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Old 04-21-2023, 07:03 PM
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So Wally hit the nail on the head. The fix was very easy. I had this sending unit installed by the marina down the street several years ago. You are supposed to remove the rheostat with the float, cut the channel to length and reinstall the float. He installed it upside down making the gauge work in reverse. I removed the 2 screws and flipped it over reinstalled problem fixed. Thanks to everyone for their help.
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