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BJ8 Fuel Gauge -Shows 1/4 tank when empty

Sprocket

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I'm curious too, as my BJ7 shows Full until I"m at about a 1/4 tank and then it bounces around (time to buy gas!) between 1/4 and F.... Been that way since I got the car from my Dad (orig owner). He used a yard stick with ballpoint markings in it to check the fuel, lol.
 

Lotuswins

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Hi Steve,

I recently had to recalibrate my guage, so it may be one of two things:

1) the tank sending unit may need tweaking. It is a rheostat with a float, and it may be off a little. You can bend the float arm slightly to get it centered where it needs to be. I was able to move the float by hand from the top of the tank to see if it was max/min at the end of travel by pushing on the wiper. Be very careful not to bend the wiper that rests on the resistor, it is fragile.
2) the guage may need calibrated to suit the tank sender. This is difficult and not for the squemish. Look in the archives for more details, there is one thread which will refer you to a MG site where a talented fellow took his guage fully apart and explains the inner workings and how he calibrated it. I basically emulated two resistances, full and empty, on the bench and finally got the guage to work properly though it doesn't seem too linear. I also broke one of the hair size conductors and had to re-solder it, that was fun.....8^).

There is also a thread about having a sender in the tank reversed but can't recall the symptoms.

I hope this helps,
 

steveg

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Gents, my fuel gauge shows 1/4 full when the tank is in fact empty. Any advice on what the problem might be?

steve

The usual reason for this is the sender is mounted 180 degrees out. If the wire is coming out of the front side of the sender, this is true. The wire should be on the rear side of the sender.

If the sender is 180 degrees out, the float will not go down into the well at the bottom of the tank and will settle on the floor of the tank which will show 1/4 tank when the tank is in fact empty.
 

Jerry

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When you read all the possible solutions, adjusting the fuel gauge is very sensitive. There are two very fine wires that are attached to the nuts on the back. These nuts are attached to the wires and when you move the nuts, the needle with move in the direction of the movement. NOTE: I have broken the wires doing this adjustment. Try the other two fixes listed above first.

Jerry
 

BJ8Healeys

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When you read all the possible solutions, adjusting the fuel gauge is very sensitive. There are two very fine wires that are attached to the nuts on the back. These nuts are attached to the wires and when you move the nuts, the needle with move in the direction of the movement. NOTE: I have broken the wires doing this adjustment. Try the other two fixes listed above first.

Jerry

The two adjusting studs to which the nuts are attached have guide feet (inside the gauge) that slide in the adjusting slots. When loosening the nuts so the studs can be moved for adjustment, you have to keep outward force on the studs to keep the feet from coming out of the slots (which you can't see because they are inside the gauge). If they do, the studs will spin when tightening the nuts and will break the coil wires, rendering the gauge inoperative. The nuts should only be loosened JUST ENOUGH to move the studs with some effort.
 

BJ8Healeys

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steveg

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I went through all the exercises including building the MGA tester on the guru site above. What I accomplished was breaking the two spider-web thin wires inside the gauge, messing up the tinfoil needle and also the hair-thin wire inside the sender. I sent the sender and gauge to APT in Minnesota and they calibrated the two together and straightened the needle.

APT: https://www.gaugeguys.com/

If mis-orientation of the sender isn't the problem, suggest sending the sender and gauge to APT and have them sort it out. If you start messing with the gauge, unless you're Gepetto the Watchmaker, you're probably going to break those wires anyway as I did.
 
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In ordee to avoid being misled by an inaccurate fuel gauge simply rely upon your resettable tripometer. Your car'S mpg will not vary more than a few percentiles from tank to tank.
 
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