Fuel gauge reads Empty when Full and vice versa!

richardsussex

richardsussex

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I have a fuel tank which came with a mechanical fuel gauge sender unit, which was pretty unsatisfactory for all the usual reasons.

So I thought that I would invest in an "electronic" sender unit, ie having a stainless steel shaft with a float that goes up and down and varies the resistance across the two connecting wires.

Checked it with a meter and a battery before fitting and the voltage went up and down with the float so I then installed sender unit and connected up.

Make (no model no.) of sender unit is "SGS Automazione Srl" - who look like a large company making control gear and didn't reply to my email - and the panel mounted gauge is "Teleflex" (which I think is a reputable brand).

Well, it worked except that when full the gauge reads empty and vice versa. Changing the polarity of the connections to the meter didn't help as, predictably, the needle just tried to go the other way.

Clearly the sender unit is constructed in such a way that the shaft is "the wrong way round" and when empty is showing no resistance and when full virtually open circuit when the opposite should be the case. So the gauge reads full when empty and as the tank level falls the needle moves to the left. I suppose I could stick "E" and "F" labels on the meter glass as a workaround but having got mild OCD like any good yottie I wouldn't be happy with that!

I just can't think of a solution as mechanism is sealed. Also these sender units are c£60 even on eBay so I would like to know if there is more than one "Type" to look for?

If we can take as read any jokes about the manufacturers possibly being the people who made Italian wartime tanks with 3 reverse and 1 forward gear, that would be good .

All suggestions gratefully received

Thanks
 
You have a US sender with a European gauge or vice versa - its a fairly common fault if people don't know to match them or like you have a legacy sender and don't know what spec it is. You can either live with it and you'll still know when empty and full just backwards or find out what spec the gauge you just bought is (it should say Euro or US in the paperwork) and then buy the other one to match your sender
 
More likely the float arm sits in a small screw clamp in the main unit around which it pivots. This will have a short end on one side and a long end (with the float attached) on the other. Unscrew it and reverse the end the float is at (taking care to have the position along the arm the same after replacement). Only a problem if the reversal places the float at the end of the tank as it should be close to the middle from memory.

Should be an easy fix. Unscrew, flip it round. Re-screw.
 
I have a similar unit with a ~30mm dia tube with a float inside which slides up/down a resistive wire. It is the change in resistance the gauge detects. Could your unit be upside down? Could the internal connections be measuring the resistance top to bottom rather than bottom to top (or vice versa). Are you sure there is no switch on the gauge or alternate connection points? Andrew
(Mine came as a set of sender and gauge,VDO, with my new tank. To shorten the tube to match the tank depth the supplier replaced the original wire with normal wire and couldn't work out why it didn't work . . . He bought me a new replacement sender unit and I sorted it.)
 
Trident said:
You have a US sender with a European gauge or vice versa ...
Click to expand...
There are indeed two main standards: high resistance when full, and high resistance when empty. There are also a couple of ranges of resistance, so it's a bit more complex than US/European.

This can be sorted out electronically, but would be unlikely to be linear without additional processing.
 
I've come across this just recently. There are 2 general groups of swing-gauges: the high-resistance = Full being the (out here at least) more common type.
If you can open the tube and invert the sensor board that is one cure, but the easiest will be a new gauge. Inverting the contents of the tube is not bad if you can use a soldering-iron in anger, but otherwise I see a trip to your local swindlery in your future!
 
Cut out a piece of paper the same size as the card on your guage dial. Mark an "E" on the new card where the "F" is on the old one and an "F" on the new one where the "E" is on the old one. Paste it on top of the old card. Voila!
 
nigelmercier said:
There are indeed two main standards: high resistance when full, and high resistance when empty. There are also a couple of ranges of resistance, so it's a bit more complex than US/European.
Click to expand...

+1.
Everyone else, think about it: with the moving arm type of sender, resistance increases as the float rises; with the OP's tube-type sender, resistance decreases as the float rises. Changing one for the other will cause the gauge to read exactly as the OP describes. Yes, a US-v-European mismatch would cause inaccurate readings, but it would not reverse them.

The problem is that the gauge is inappropriate for the sender (or vice versa). Without changing one or the other, there's no ready solution.
 
Hello

I have the same problem. I have a Faria fuel level gauge (USA) .
1590123082706.png
That gauge works with 240 - 33 Ohm.

You can see in those links:

- https://www.fariabeede.com/site_manuals/IS0100_L_Warranty_Repair_guide.pdf

- https://fariabeede.com/site_manuals/IS0100q.pdf

But......

1590123276847.png
1590123718036.png
I have a 33 - 240 Ohms not 240 - 33 Ohms. Thats why the Gauge works in reverse.

This is my sensor
1590124124024.png

This is the schematic

1590124166186.png

And this is the schematic of the correct sender.

1590124474683.png

So, the guy that made my sensor, forget one important thing, the resistence of the sensor for USA is in Reverse.

The problem that you have is an European gauge with Usa sensor or Usa gauge with European sensor.

All the best for you.

Pedro Cereja
 
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