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Fuel Gauge

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Michael Oritt

Michael Oritt

Yoda
Gold
Online
The fuel gauge in my 100 has suddenly stopped working with the needle pegged at E - this with both 1/2 and full tanks.

The bulb in a test light is full bright at the green power lead and considerably dimmer at the green/black tank lead. I have not tried getting any ohm readings between the two as I am not sure what I should be seeing.

Suggestions appreciated.
 
Well over 100 views and no responses. I was going to write a missive about this but realized that the web provided a better summary than I'd produce. I'm guessing you've fixed it or at least diagnosed it by now. If not even if you are no fan of AI, Google is still your friend on this one. There are dozens of appropriate youtube videos on classic car fuel gage issues. Here is a video that pretty much sums it up.
 
The MGA Guru site has several articles on the fuel gauge and sending unit. See the FG articles on this page.
 
roscoe said:
Well over 100 views and no responses. I was going to write a missive about this but realized that the web provided a better summary than I'd produce. I'm guessing you've fixed it or at least diagnosed it by now. If not even if you are no fan of AI, Google is still your friend on this one. There are dozens of appropriate youtube videos on classic car fuel gage issues. Here is a video that pretty much sums it up.
Click to expand...
John--

I have not had a chance to get into diagnosing/fixing it yet but hope to on Tuesday. The video you just sent will be very helpful.
Assuming i get down to pulling the sender and it is still functional I will try to dampen the arm's action as suggested elsewhere.
Many thanks.
 
There is 0 resistance (continuity) between the green/black sender lead at the gauge and ground. I'll empty the boot tomorrow and see whether the lead itself is grounded somewhere or if the issue is in the sender itself.
 
This morning I detached the green/black wire from the sender and checked to see if there was continuity between it and ground which there was not.
I removed the sender from the tank and attached the leads of a test meter (set to measure ohms/continuity) to the body and the output contact. There was continuity along the entire range from what would be empty to full. The wipers appeared to ride nicely along the coil but the needle did not come off the peg, so I assume the sender is defective.

Except for the fact that I simply like to have things in working order this is not a critical matter as my car gives a reliable 20-22 mpg and I normally rely upon the resettable tripometer to tell me when I need fuel, so I'll reinstall the gauge in a non-operative mode tomorrow pending a solution.

I recently replaced the tach and speedo with electronic units from Speedhut and they also make a 2-1/8" diameter fuel gauge. I'd like to use their optional sender but its minimum height is 7" and the depth of the 100's tank is just under 5". Has anyone replaced the stock sender with an aftermarket sender and if so how has that worked out?
 
Last edited:
Michael Oritt said:
This morning I detached the green/black wire from the sender and checked to see if there was continuity between it and ground which there was not.
I removed the sender from the tank and attached the leads of a test meter (set to measure ohms/continuity) to the body and the output contact. There was continuity along the entire range from what would be empty to full. The wipers appeared to ride nicely along the coil but the needle did not come off the peg, so I assume the sender is defective.

Except for the fact that I simply like to have things in working order this is not a critical matter as my car gives a reliable 20-22 mpg and I normally rely upon the resettable tripometer to tell me when I need fuel, so I'll reinstall the gauge in a non-operative mode tomorrow pending a solution.

I recently replaced the tach and speedo with electronic units from Speedhut and they also make a 2-1/8" diameter fuel gauge. I'd like to use their optional sender but its minimum height is 7" and the depth of the 100's tank is just under 5". Has anyone replaced the stock sender with an aftermarket sender and if so how has that worked out?
Click to expand...
Michael, I thought I had mentioned that I have a speedhut fuel gage in use with a sender I have been using since I rebuilt the car. I think I bought the sender from either Moss, Victoria British or an eBay supplier and was using it with my original gage until I tried to fiddle with the
innards and totally goobered up the gage. The speed hut gages come with several preset ohm ranges you can easily program or you can do the full/ empty calibration to match what ever ohm range they don't provide. Mine seems to work well with the old sender which supposedly was the same as original. My recollection is that we all have as original 0 to 90 ohm approx. senders. Also, I sent you a pm a few days ago, did you see it?
Jon
 
Hi again John--

Speedhut says their fuel gauge is compatible with any sender. Although the sender that just broke is original and did last 70 years I'd like to get a "modern" one that has a vertical float rather than an arm which is very sensitive to fuel movement, etc. As I said, this is not an essential need and I'll just stick the gauge back in place and rely on the speedo's resettable tripometer for a while while I'm searching for Mr. Right.
 
John--

Though I know the sender is defective I assumed that the gauge was okay. However, when I put it on a bench power supply (unregulated 12 VDC) I see that the needle barely jumps off the peg by "E"--this regardless of which way I wire it.

Is it possible to test the gauge without a sender or the like to regulate the power?
 
Michael, the sender is just a variable resistor. Do you have / can you get a ~90 ohm resistor? Did you look at the articles on the MGA guru website?
 
Hi Bob--

No, I do not have a 90 ohm resistor and though I am sure I can get one I still need to get another sender--just deciding whether to use a stock one or anb aftermarket, all of which seem to use a five-hole mounting pattern which would require either drillin one which would require either drilling and tapping new holes in the tank flange or making a conversion plate with both bolt circles.

I was simply hoping to find a way of testing the gauge itself with what is on hand.

I did read the articles.

Thanks for your reply.
 
Bob--The meter I have on hand does not allow me to change the resistance. In any case I've decided to simply get a stock sender with the Speedhut gauge.
 
I'm not sure how this has gone a bit astray but here is a summary of how to trouble shoot the Healey fuel gage system with no resistors, volt ohm meters or other complications.

To find out if the problem is in the gauge or the wire leading back to the tank: [1, 2]
    • Turn the ignition key to the ON position. [1, 2]
    • Go to the rear/tank area and disconnect the green-and-black signal wire from the fuel sending unit. [1, 2]
    • Ground the wire directly to the car's metal frame or chassis. [1]
    • Look at the dashboard gauge:
      • If the gauge swings to "Full" (or past it), your gauge and signal wire are working properly. The fault is inside the fuel tank.
      • If the gauge does not move (stays on empty), either the gauge is bad, the power feed to the gauge is dead, or there is a break in the signal wire. [1, 2]
    • Next, pull the wire off the back of the gauge itself and ground that terminal directly. If the gauge moves now, the wire running under the car is broken. [1, 2]

2. Test the Sending Unit (Resistance Check)
If the gauge and wiring pass, remove the sending unit from the top of the fuel tank to test the internal rheostat and float: [1, 2]
    • Disconnect the wire and set an ohmmeter (analog meter works best) between the sender's terminal and its body/ground. [1, 2]
    • Move the float arm manually through its full range of motion:
      • Empty position (float down): Should read roughly 70 to 73 ohms.
      • Full position (float up): Should read roughly 8 to 10 ohms. [1, 2, 3, 4, 5]
    • Common Healey issues to check for:
      • Sunk float: Many classic plastic floats degrade or crack from modern ethanol fuel, fill with gas, and drop to the bottom (making the gauge read empty permanently). Swap it for a brass float if needed.
      • Bad ground: Ensure the sender housing has a clean, unrusted electrical ground to the car body. [1, 2]
 
Jon--

The gauge is broken--the needle does not come off the E-peg, power or not.
The sender is bad as well--I checked it out of the car and there is continuity between the terminal and body through its entire swing.
I'm going to replace the gauge with a Speedhut unit and the sender with a stock Healey unit as it is the best option given the relatively shallow tank and the different diameter and fastener patterns of aftermarket senders.
 
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