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Fuel Gauge always indicates 1/4 full.

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warwick-steve

warwick-steve

Jedi Hopeful
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Hi all
Before I bought my BT7 3 years ago it had a new aluminium fuel tank fitted and I believe the fuel gauge was checked out, however. it wasn't working when I bought the car. This is one of the jobs I have put off as low priority but I would now really like to have a working gauge instead of having to use a dip stick.

When I turn on the ignition, the gauge just moves to about 1/4 full and stays there. Any ideas please?
I have made sure the gauge is well earthed.
Is it likely to be the gauge or the sender?

All help appreciated
Steve
 
"Is it likely to be the gauge or the sender?"

Yes.

Hilarity aside, gas gauge insubordination is a common problem in older cars. The gauges can be adjusted, but the senders usually can't beyond bending the float arm and making sure the float hasn't sunk. Replacement senders are available--I bought one off eBay a while back that appears to be good quality (for about $50; about a pound-and-a-half these days)--but haven't installed it. Make sure the sender is well grounded, and check continuity along the wire; your problem is probably the gauge, but swapping senders is easy and relatively cheap and I'd start there. I think there's some online info on how to adjust the gauge--'MGAGuru' maybe--but it's a touchy operation and I'd probably leave it to a pro or purchase new. I believe you can diagnose the sender by checking resistance along the wound wire coil.

Here's the sender (I think) I bought; looks like prices have come up:

https://www.ebay.com/itm/New-Fuel-T...J9aRyGG:sc:USPSFirstClass!95117!US!-1&vxp=mtr
 
Before you buy a new sender or have your gauge repaired suggest simple test setup. As you move the float through its arc, you should see the needle move accordingly.
MGAguru has an article about building a switch using resistors that can be used to test the gauge separately from the sender.
Be extra careful undoing the stock wire from the terminal on the sender as you can break the fine internal wire attached to it on the inside.

screenshot.1140 (2).jpg
 
Hi Steve,

In concert with Bob and Steve, the sending unit receives its ground through the metal fuel line connection between the unit and the fuel pump. Over the years, many have severed this fuel line to install a fuel filter and the solid ground was lost. Since this solid sender ground is required to present a consistent level of resistance to reflect a specific fuel level to the gauge, if a ground is even present, it is the result of it being sourced through a found less precise electrical path. If this is your situation, I would attach a ground line between one of the screws on the sending unit and a convenient contact on the frame.

As I remember, 2 adjustment nuts are located on the back of the gauge that affect the pendulonic response of the needle, therefore, the reading of the gauge. When slightly loose, these adjusters ride on an incline plain moving the coil closer or further away from the needle mechanism and will alter the pointer's position.

Before adjusted the sender or gauge, I would first follow the suggestion of Bob and Steve and carefully read the article referenced.

As I remember, when adjusting my gauge, I first determined the tank's capacity to understand what Full would mean and where Empty should be. Additionally, there is a bulge in the bottom of the tank just below the location of the float. This bulge is to provide a reserve when the needle is pointing to Empty. When setting the gauge to Empty, I filled the tank to the reserve capacity and adjusted empty to that level. Next, I filled the tank to the Full level and set the gauge to FULL. After each adjustment I carefully snugged the nuts to assure they remained in position.

Keep in mind that the gauge will only register with the ignition on. This condition and the fact you will be working with fuel are 2 conditions that warrant extreme care. As previously stated, I strongly suggest you carefully read the document referenced by Bob and Steve as I performed this task a while ago and could be forgetting something important.

Be very care,
Ray(64BJ8P1}
 
IMO it's very easy to break one of the hair-thin internal wires if one starts trying to adjust the two nuts on the back of the gauge. I know because I've done it. Then I sent the gauge and sender off to The Gauge Guys (UK & Minnesota) to undo my errors.

Probably should have mentioned above - make sure the float is oriented such that at empty it drops into the well. Forward, pointing, IIRC.
 
Float arms can also get stuck due to corrosion and/or deposits in the tank. Unfortunately repair involves removal of the sending unit and manipulating the float arm while you keep the sending unit as wet with carb cleaner as you can. In addition to stuck float arms, floats can become perforated, take on fuel, and sit at/near the bottom of their travel. Again, checking this out and repairing it requires removal of the sending unit.

As Steve G. said, the windings inside the gauge are delicate. They become more delicate with age as heat and time make some of the insulator materials brittle. Exercise caution when you work with gauge calibration.
 
Steve, thank you for stressing the sensitivity of the gauge adjusters. I tried to imply that by indicating that they should only be slightly loose but may have missed the mark. When dealing with any gauge, you should be very careful and treat any component with timidity.

I hope all have understood that when dealing with any original dash component, you would be doing it at your own risk so be very careful as everything is OLD.

Ray(64BJ8P1)
 
Gentlemen
Thank you for all the valuable information. I will look at the MGAguru info and take it from there. I suspect that it is the gauge but will check out the sender first.
Cheers
Steve
 
steveg said:
....

Probably should have mentioned above - make sure the float is oriented such that at empty it drops into the well. Forward, pointing, IIRC.
Click to expand...
So that's why the float arm points forward. It would have been more accurate if the well were in the middle of the tank so the float would be in the middle instead of at the extremes when the fuel moves left-right and/or front-back.
 
I don't know if this will help you but it fixed my gauge in my Bugeye.

The gauge said !/4 full when I turned off the ignition. The problem was that the gauge on the dash was turned to the left slightly. When I straightened it the gauge went to Zero and no more problems.
 
Great Demo Steve,

People can finally SEE how the sender should be positioned and why.

Good job,
Ray(64BJ8P1)
 
steve
thanks for the info. i too noticed my gauge was registering about an 1/8 of a tank during an electrical test and i don't have fuel in it. checked it and sure enough it was pointed the wrong way. the easy way to tell i guess is to see that the electrical stud is at the back end. i bet a lot of people, including me, thought it should go towards the front, closer to the wire.
 
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