Fuel Gauge Not Reading Right

[mxp01]

Gentlemen:

I know this question has been addressed repeatedly, but I'll ask again:

The fuel gauge in my BE reads either full or empty. Also, the gauge will only activate when I tap it. I have used two different fuel gauges and I have replaced the sender. There is a ground at the gauge and let me explain why:

- I hooked up the gauge and without the ground I turned on the electricity. The gauge did not read, even when tapped, but I could feel a small jolt of electricity around the gauge as I held it in place. After I turned off the juice, I hooked up the bracket, attached the ground, turned the juice on again, tapped the gauge, and it read full.

The last thing I can think of doing is hooking up another ground wire at the fuel tank to ensure a ground there.

Otherwise, I'm stumped.

Mike Pennell

 

[dklawson]

It sounds like you've already given this careful thought.

Have you visited the MGA-Guru web site and gone through Barney Gaylord's inspection and calibration methods? If not, it's well worth reading and trying some of his maintenance steps.
https://mgaguru.com/mgtech//electric/fg_01.htm
(Follow the additional pages by clicking the "forward" link at the bottom of the page.)

 

[mxp01]

There's actually a wrinkle in this:

I took the car out tonight for a ride. When I turned the key the gauge went to full. When I turned on the lights the gauge went to empty.

Any ideas?

Mike Pennell

 

[Bayless]

First, that gauge has to be grounded or it will always read empty. If it goes to hard full and the tank is not then that suggests a break or bad connection in the wire between the gauge and the sender. A bad ground at the sender will do the same. If it goes to hard empty then that suggests a short in that same wire. I really don't think the lights are related. Be sure you have a green wire to the B post of the gauge and a green/black to the T post. The case must be grounded. If you remove the green/black from the T post and check its resistance, it should be somewhere between 0 (empty) and 70 (full).

 

[dklawson]

Just to second Bayless' comments, grounds and broken wires on the early gauge system show up "differently" than they do on later cars.

The early Mini used a similar gauge system but the sending unit had a slightly different resistance range. While working on my Mini I wrote a PDF for a guy in the U.K. showing him some of the wiring and documenting my observations. Maybe something in that will be of interest to you. You can see a copy of it at:
https://home.mindspring.com/~purlawson/files/OldFuelGauge.pdf

However, Barney Gaylord's MGA-Guru web pages on the early fuel gauge are the Bible on this system. If you haven't read through those pages yet, it will be to your benefit to do so.

 

[regularman]

The only way I found to get them right is to calibrate the sender and gauge together. You need to syphon all the gas from the tank and get an ohm reading and then top the tank off and get another ohm reading, then first make sure you have the correct gauge and the range of the gauge is correct by using resistors, then connect it all up with a gound connected to the gauge and also one from the frame (good ground spot) to one of the nuts that hold the sender on just to be sure of a good ground.

 

[mxp01]

Gentlemen:

My son and I were working on the fuel gauge tonight. Here's what we have done:

- We took the fuel tank down and the float out. Everything is still wired up.
- We popped the fuel gauge out of the dashboard.
- With the sender wired and grounded we checked the level of the gauge. The best we could get was full but empty at around a half tank.
- We popped the green/black wire off the gauge. While I moved the float from empty to full. We recorded Ohms of 3 (empty) to 85 (full).

Note: We have converted the car to negative ground. I have a Series II sender and a Series II gauge (FG2530/70). It is a 1960 BE with a ne wiring harness. However, the small length of wire from the end of the wiring harness (in a butt connection) to the sender is original.

We still aren't where we need to be. Any suggestions?

Mike Pennell

 

[dklawson]

The early fuel gauge case must have an earth connection for the gauge to work. I'm surprised you got any reading at all with it out of the dash.

Series II covers what years? (Sorry, I don't know my Spridget evolution).

If Series II is before the mid-1960s, the gauge system will be "early" without the voltage stabilizer. The resistance reading you took on the fuel sending unit are consistent with the early gauge system. Therefore, I suggest you visit Barney Gaylord's MGA-Guru web site and read over the early gauge system. He has several pages that start by explaining how it works, then he walks you through calibration.

https://mgaguru.com/mgtech//electric/fg_01.htm

Once your comfortable with how the system works, you will probably find calibrating your sender to your gauge (as Kim suggested) will get you where you want to be.

IF the gauge system changed during Series II production, you will need to make sure that you have an early gauge to work with that early sender.

Footnote:
When I loaded the MGA site tonight the links to move forward and back from page to page were not clearly labeled. I only found boxes with red "X"s in them at the bottom of each page. Those red "X"s should be forward, back, and home icons/arrows. The right most "X" is "forward" and will take you to the next page.

 

[Bayless]

According to Haynes, the MKII and MKIII Sprite still used the early gauge.

 

[mxp01]

Doug:

Quoting Bayless:

"Be sure you have a green wire to the B post of the gauge and a green/black to the T post. The case must be grounded. If you remove the green/black from the T post and check its resistance, it should be somewhere between 0 (empty) and 70 (full)."

We had the tank grounded. My son said that the green/black wire ran directly from the sender, so it carries an electrical current.

Are we doing this right?

Mike P.

 

[dklawson]

Mike,

Bayless is correct. My comments in my last post were about the earth connection to the gauge itself. You said:
"<span style="font-style: italic">- We popped the fuel gauge out of the dashboard.</span>"
The gauge will not operate properly when it is removed from the dashboard unless you run a ground wire to its case.

Take a look at the MGA-Guru web site I posted a link to. Barney writes very well and his web pages will give you a really good understanding of the early fuel gauge, how it's works, and how to troubleshoot and calibrate it.