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Fuel gauge trouble TR2


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Hi There,

I do have trouble with my fuel gauge since I have the car and decided to evaluate the root cause now: When turning on the ignition, the needle runs up and everything looks normal for 2-3 secs . After a few secs however, the needle jumps all over the place. This does not Change when I start up the engine.

I have checked the connections and could not find any obvious defect.

I do have a voltage regulator fitted (TR4 config) which I do consider to be unsuspicious as all other gauges connected to it are indicating all right and the fuel gauge error does occur as well when the engine is not running.

Next step would be to check/ replacement of the Sender unit....

Any further Input or similar experiences in this community?

 

Any advice welcome

 

Cheers

Oliver

 

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I assume that since you have a voltage regulator, the fuel gauge is also from a TR4? 

That later type fuel gauge is a bimetallic strip device. As such its indication should only change slowly as it is driven by the strip bending with temperature, and the temperature cannot change very quickly because of the thermal mass. In what way is the needle jumping?  If it is moving about rapidly there may be something wrong with the mechanical linkage inside the gauge. 

I believe the TR4 tank sender varies from (about) 240 Ohms to earth at empty to 20 Ohms to earth at full, so if you have a suitable resistor within that range you could substitute that for the sender connection and see whether the gauge reading steadies. If it does, suspect the sender or its wiring, if it stays erratic it is the gauge at fault. 

This link describes what is inside:

http://www.mgb-stuff.org.uk/fuel.htm

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It sounds to me that you have the original moving iron fuel gauge but powered from the voltage stabiliser. As the voltage stabiliser warms up, & starts to interrupt the supply to the fast reacting gauge it will jump around.  If I am right, & this is the case, connect the "B" terminal of the gauge direct to the ignition switch, & not via the stabiliser.

Bob.

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Yes of course, that will do it - good thinking Bob.  

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Posted (edited)

Thank Y'all for the Input!

Just for the avoidance of doubt: It Looks like all gauges are connected to the stabilizer but with only the fuel gauge jumping.  (The needle really jumps up and down fast like a seismograph)

Edited by Moliver
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Oliver,

 

One of the first things that broke (that I broke…) on my 3A was the temperature gauge capillary tube. I replaced it with an electric sender and a bi-metal gauge.

Maybe that is what has happened here, and the PO has wired up both the new temperature gauge and the original moving iron gauge through the voltage regulator.

(Is your temperature gauge sender electric?)

Don’t remove the fuel sender just yet. If you do you’ll have all the hassle of making it leak proof when you refit it.

Charlie.

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I assume you've checked the earth on the sender. I'd run an extra lead from one of the flange mounting nuts if not. Why the stabilizer, are you using later gauges?

You can check the sender by grounding the terminal. The gauge should go to full and stay steady. If it still acts up with the terminal grounded, the fault is probably not in the sender.

Tom

Edited by TomMull
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No.  The original type gauge will go to empty if you ground the sender wire.

If the needle is moving at all quickly then it is not the later bi-metalic type, & I stand by my earlier diagnosis, & fix.

Bob.

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  • 4 weeks later...

Hi all,

I have further investigated.

0) Basic Situation: Gauge connected to Voltage Regulator, Earth and Sender terminal:--> With ignition on it jumps to "Full" after 30 sec it jumps up and down from empty to full .

1) Sender unit disconnected and Batterie direct to the gauge battery terminal (without VR) -  Gauge reads full - Then Earth to the Sender Terminal - gauge reads empty.

--> I read that the gauge itself should be all right (see attached doc)

 2) Now, Sender unit re-connected, batterie still directly connecetd without VR (Bobs proposal/ TR2 wiring spec):

needle still Jitters around 1/2 (which is about correct tank level). If I open the tank and push the Sender down with a rod, the gauge reacts a Little but not to the level it should-

--> I read that the direct Connection without VR helps, and Sender unit shall be quetioned. Will check/ replace Sender and will eliminate the VC for the fuel gauge.

 

Nevertheless, I would like to understand the VR implications: For which gauges a VR is required  and why has a VR been implemented with the TR4 ?

What happens if I take out the VR for all gauges ?

All gauges are Jaeger (except the batterie voltage gauge which is Lucas)

The fuel gauge no is: X.49422/220 PG.163

Some lessons welcome.....

 

Cheers

 

Oliver

 

 

Fuel Gauge Care_of_Instruments.pdf

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Hi Oliver.

From above I would say your fuel gauge is fine, & should be used without a Voltage Stabiliser. The cause of a wobbly needle with tank half full is probably a bad connection between the resistance wire in the sender, & the wiper which moves along it. It is not too difficult to take the sender apart (carefully) & clean up the contact area on the wiper, & also along the length of the wound resistance wire. very fine wet & dry will restore a clean surface, but make sure all dust is blown out before re-assebly.

Bob.

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  • 4 weeks later...

I have just had to place a wedge between the fuel tank and the braces to raise the tank to a point where the fuel tank opening lines up with the fuel cap.  It needed to be tilted toward the rear of the car.  My next project is to get the fuel gauge working.  Will the new angle of the fuel tank affect the sender's operation?

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I would not expect any problem unless the tank is now at a vastly different angle to normal.

Bob.

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On 9/13/2020 at 1:36 PM, Lebro said:

Hi Oliver.

From above I would say your fuel gauge is fine, & should be used without a Voltage Stabiliser. The cause of a wobbly needle with tank half full is probably a bad connection between the resistance wire in the sender, & the wiper which moves along it. It is not too difficult to take the sender apart (carefully) & clean up the contact area on the wiper, & also along the length of the wound resistance wire. very fine wet & dry will restore a clean surface, but make sure all dust is blown out before re-assebly.

Bob.

I had the same issue as the opening poster. The guage never used to flicker and then one day it just started. I had the added issue in that the guage would read 1/4 full when it was empty (took me 23 years to find that out as I never let it get lower than this until it just died). 

         I found the fault for the flickering to be exactly as Bob has described above. The level was fixed by a little bend on the arm but also a slight alteration to the angle of arc of the sender as it appeared to be catching the side of the tank on the way down which might have been the root cause for the level inaccuracy (but I don't really know as I bent the arm slightly before realising the float touched the sides as it went down). It now shows empty on the tank before I run out, and still reads full if I put a reasonable amount in. 

   But for the opening posts issue I would second Bob's analysis as a good starting point. Didn't have an issue selling the tank and getting rid of the petrol smell myself. 

Neil

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Bob is the Expert on the fuel gauge. I took mine to him with the sender and he overhauled ,cleaned and fixed all problems. he explained that they need to be matched together. Since then I have had no further problems in that area. I think that the gauge reads empty with still one gallon inside. This may be a safety design so that you do not run out by mistake. Send all the kit to Bob in Leatherhead Surrey and move on to the next problem.

On a related topic it is best not to use a tank sealer to protect the inside of the tank. 

Good luck Richard & B

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1 minute ago, Richardtr3a said:

On a related topic it is best not to use a tank sealer to protect the inside of the tank

This is not my experience, Richard. I sealed up my tank some ten years ago, maybe more, with a French epoxy solution and up to now it has worked well. No rust flakes in the fuel filter bowl! Pain in the neck to do it though....

james

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15 hours ago, Lebro said:

I would not expect any problem unless the tank is now at a vastly different angle to normal.

Bob.

 

Hi Bob,

The reverse happened.  Aligning the tank properly appears to have freed the float.  The gauge is working very well now.

Dumb luck on my part.  It's the first time, since I bought the car, that all the gauges are working properly.

Cheers,

David

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On 8/14/2020 at 10:14 PM, Lebro said:

It sounds to me that you have the original moving iron fuel gauge but powered from the voltage stabiliser. As the voltage stabiliser warms up, & starts to interrupt the supply to the fast reacting gauge it will jump around.  If I am right, & this is the case, connect the "B" terminal of the gauge direct to the ignition switch, & not via the stabiliser.

Bob.

Bob,

Does this mean that the TR4 wiring diagram on the Advanceautowire website is incorrect? 
Graham

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This topic was about a TR2, not a TR4  My response above was related to TR's 2 to 3A which have a different fuel gauge system to the later cars.

A TR4 will use a voltage stabiliser, & a slow moving fuel (& temperature) gauge.

Bob.

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Hi All. Just wondering if I can jump in with a related question. My full gauge wasn’t wired up when I bought the car and always read empty. 
 

I’ve now wired it up and it shows what is probably a correct reading about 3/4 full if the ignition is on, but goes to full (not empty) when ignition is off.  It won’t go back to zero any more.  Ignition on = a reading, ignition off = full?

no obvious grounding of the signal wire from sender unit to gauge   
 

ive also tried earthing the gauge and sender unit separately  

Any thoughts or help?

Edited by Richard TR2
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Are you sure that with ign off there is no voltage on the gauge.  The gauge will normally only go to full if a) you have a full tank , or b) the sender is disconnected.

But both situations require 12 Volts on the gauges  "B" terminal coming from the ignition circuits.

Bob.

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