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Fuel Gauge - Help Needed

andrewss

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I have installed a much larger alu fuel tank in a BN1 100/4. The fuel tank has a side fitted fuel sender which was copied from the jaguar XK140/150 fuel sender. It has two connectors (I believe one to measure the actual fuel level and the second for measuring the reserve tank which i don't have).

I have standard Smith's fuel dial. The two do not seem compatible !! Both the sender and the gauge are earthed and wired correctly. From both the top and bottom contact on the sender i am getting a full reading which I know is not the case as the fuel tank is near empty...

Do I need to find an alternative fuel gauge ?

Any help appreciated...

mQBTsJWOUGgpG01N9x98Qhg.jpg
 

healeyblue

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The sender may not have the correct ohm range. Is the gauge stock? What is the sender for? The MGB also has the sender in the side of the tank.
 

dh100m

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with the old tank the sender body is grounded ,if the grounding is bad ie open circuit the gauge will go full scale try grounding one terminal of your new sender
 
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Here's my setup; I used the aftermarket replacement sending unit for the Healey's tank. One (1) wire is all I needed to make it work. The gauge reads "full" until the level gets down about halfway, then actually starts responding to the level in the tank.

Everything worked like a charm for over a decade, but the resistor has recently taken a dive__I'm waiting for the level to get low enough to get the sender out and see what's up.

In your case, what happens when you "ground" the (one) wire from the sending unit? IIRC, the gauge should read "full" (or "empty?) and as the resistance goes up, the reading on the gauge goes lower (or higher?). The gauge being merely a voltage meter, where "full" (or empty, whichever the case may be) equates to it getting the full 12VDC (no resistance in the grounded feedback wire).

IMG_6648.jpg
 

blueskies

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Both the Jaguar and Healey gauges should be magnetic gauges. If everything is wired and grounded correctly and both parts are good, the gauge should work, at least somewhat - even if the ohm ranges of the Jaguar and the Healey sending units are not identical. Both likely register 0 at one end of their range and 80 to 100 ohms at the other end. The second terminal on the Jaguar sending unit may be for a low fuel light that comes on when the level drops to a certain level, and not for a reserve tank gauge; that should be completely isolated from the fuel gauge function.
 
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andrewss

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Update - both the sender unit (measured the resistance whilst moving the float) and the gauge are working well independent of each other. As healeyblue highlighted I think the problem relates to the Ohm range which seem to completely different. I need the XK150 sender unit as its the only one that has a long enough arm to reach the bottom of the tank.

So taking that as a given can anyone recommend a compatable fuel gauge preferably 'Healey looking' ?

Regards,

Andrew
 

healeyblue

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Measure the Ohm range of the sender you intend to use. Its easy to do and is a value you will need to know to make your selection for a gauge.
 

catfood

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Try googling spiyda design. They manufacture a box of electronics that provides the calibration for you. Not used one myself but a friend has had some success in a kit car he buil
 
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andrewss

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The fuel sender operates between 80 ohms empty and 2,2 ohms full. The only make/model that I can find thats suits this sender is a VDO Series 1 that has an operating range of 0-90 ohms. Its not a Smith's but I guess I don't have a choice unless the Smith's can be re calibrated..
 

TimK

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I have used Nisonger for my speedometer with great result. Easy to check with them about recalibrating the fuel gauge.
 

CraigC

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Andrew, I brought a variable potentiometer home from work today in order to test the gauge in my BN2. I will try to get to it tomorrow and post results.
 

CraigC

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It's actually 0 empty, 90 full. This is a commonly used resistance profile. Being that this is the exact opposite of what your sender measured, I would think you should be able to rotate the sender mounting position 180 degrees to achieve the needed operating resistance. Looks like the stock 6-bolt mount pattern by the pic in your first post. Could you post a pic of the tank as well as of the actual sending unit?
 
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andrewss

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Craig - Thank you so much for taking the time to check for me. Your solution will indeed work. I will post a picture of a 'happy man and a fuel tank' later today..
 
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