New fuel sender unit

[Jeepster]

Finally got around to installing my new fuel tank today along with a new fuel sender unit.
I have connected the sender wire to its terminal but should there be a ground wire? Mine doesnt seem to have one.

When the ignition is turned on the gauge reads full even though there is hardly any fuel in the tank. I did try a temporary ground wire from the screws that hold in the sender to the body work but this made no difference at all.

I know the gauge works as it did before the new tank install ( it had a non Healey tank and sender)

 

[Keoke]

I did try a temporary ground wire from the screws that hold in the sender to the body work but this made no difference at all

That is because the tank is being grounded via the fuel lines or physically by its instalation. However, I would leave your additional ground circuit in place as insurance OK--Fwiw--Keoke

 

[richberman]

You have a PM.
rich

 

[Jeepster]

Rich,

thanks for the email with the explanations of how to calibrate the gauge.

I haven't managed to get around to trying the calibration out as yet but it seems a long way out to start with as my gauge was working with the old sender but now it goes way off the scale to full even with hardly any fuel in. I cant imagine it will adjust all the way back across the dial to the empty mark?

 

[Keoke]

No it does not sound like an adjustment problem to me . However, I would keep the ground circuit you added in place as I suggested while you trouble shoot the problem.This will elilimate ground circuit concerns.--Keoke

 

[BJ8Healeys]

Rich,

thanks for the email with the explanations of how to calibrate the gauge.

I haven't managed to get around to trying the calibration out as yet but it seems a long way out to start with as my gauge was working with the old sender but now it goes way off the scale to full even with hardly any fuel in. I cant imagine it will adjust all the way back across the dial to the empty mark?

Jeepster, the gauge needs to be sensing the proper resistance in the sender circuit (approx. 90 ohms full and close to zero for empty) to register properly. Of course, it also has to be correctly calibrated. There are two coils of tiny wire inside the gauge -- one primarily influences the needle to the empty side, the other to the full side. If you decide to calibrate the gauge yourself, there is a caution you need to be aware of. The adjustment is made by loosening two small nuts on the back of the gauge and sliding the threaded posts in a slot. There are guide "feet" inside the gauge that follow these slots. DO NOT ALLOW THE FEET TO COME OUT OF THE SLOTS! If you do, you'll spin the coil when you tighten the nuts and you'll break the wire. Then, you'll send the gauge off for repair.

 

[shorn]

Could it be that the gauge itself is not properly grounded at the dash????

 

[Jeepster]

Could it be that the gauge itself is not properly grounded at the dash????

Unlikely as the gauge was working with the old sender and I have not as yet touched the gauge.

 

[Jeepster]

I have just had the gauge out to try and calibrate it but it does not have the 2 adjustment nuts on the back? Only 2 small holes?
The gauge is a Smiths unit and looks like the AH fitted versions.

Maybe this gauge is from a different model of car? I cant imagine that would make much difference?

Also checked the sender and this gives 80 ohms between full and empty.

 

[BJ8Healeys]

I have just had the gauge out to try and calibrate it but it does not have the 2 adjustment nuts on the back? Only 2 small holes?
The gauge is a Smiths unit and looks like the AH fitted versions.

Maybe this gauge is from a different model of car? I cant imagine that would make much difference?

Also checked the sender and this gives 80 ohms between full and empty.

Jeepster, the gauge should have two slots in the back of the case where the threaded posts can slide. It is these posts that should have the nuts. Can you provide a picture of the gauge (and the back of the gauge)?

It doesn't matter much what the actual resistance of the sender is, if you can build the test rig with the correct resistors you can adjust the gauge to accommodate the sender resistance. Of course, if the gauge expects to see 90 ohms + from the sender at full, and you can only get 80, then it might be difficult to calibrate it. I've never dealt with that problem, so I don't know.