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Fuel Gauge Reads Low Or Empty


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#1 dangerousdowning

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Posted 10 November 2018 - 06:01 PM

I've lived with this issue for years, but seeing as my mini has finally been MOT'd after 2 and a half years in my garage (just in time for winter!?!), I thought I'd actually get round to sorting it.

 

If I put a full tank in, then if memory serves me correctly, then it might show half a tank.

I put about £20 in it from empty this week and the gauge showed the level just above the red.

 

I purchased a new fuel sender a few years back, hoping to resolve it, but made no different.

 

Any ideas?

 

Thanks

 



#2 Moke Spider

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Posted 10 November 2018 - 06:16 PM

I'd suggest firstly making sue the mounting plate on the sender is making a good Earth connection. Some cars had a separate Earth Wire and some just Earth through the steel of the Tank itself, so it may not have an Earth Wire. While you are there, with the Key on, briefly short the wire going off to the Gauge to Earth, if all is well between there and the Gauge, the Gauge should shoot up past Full fairly quickly.

 

If the Earth is OK and the Gauge still reads low, then I'd say the the Voltage Stabaliser could be playing up, if it's an original, these were a vibrating reed device and so difficult to impossible to check with a Multimeter, you really need a Smiths type (thermal) voltmeter to check the output of these, which should be 10 volts.

 

If that checks out, then the only thing left is the gauge itself.



#3 dangerousdowning

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Posted 10 November 2018 - 06:35 PM

I'd suggest firstly making sue the mounting plate on the sender is making a good Earth connection. Some cars had a separate Earth Wire and some just Earth through the steel of the Tank itself, so it may not have an Earth Wire. While you are there, with the Key on, briefly short the wire going off to the Gauge to Earth, if all is well between there and the Gauge, the Gauge should shoot up past Full fairly quickly.

 

If the Earth is OK and the Gauge still reads low, then I'd say the the Voltage Stabaliser could be playing up, if it's an original, these were a vibrating reed device and so difficult to impossible to check with a Multimeter, you really need a Smiths type (thermal) voltmeter to check the output of these, which should be 10 volts.

 

If that checks out, then the only thing left is the gauge itself.

 

Thanks. Will investigate tomorrow.



#4 matt615

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Posted 10 November 2018 - 06:53 PM

What year of Mini is it? From 1992 ish onwards you need to use the injection type sender unit. This has a couple of extra bends in it to clear the fuel pump in the tank.

Even if it’s a carb model you still need this, as they standardised on parts and used the same fuel tank in all models.

If you have the wrong sender unit it will only rise so far, before it gets stuck and gives a low reading.

#5 matt615

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Posted 10 November 2018 - 06:59 PM

And as moke spider says, short the two wires together. If the gauge rises to full, you know the problem is definitely with the sender unit.

Edited by matt615, 10 November 2018 - 07:30 PM.


#6 dangerousdowning

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Posted 10 November 2018 - 07:31 PM

What year of Mini is it? From 1992 ish onwards you need to use the injection type sender unit. This has a couple of extra bends in it to clear the fuel pump in the tank.

Even if it’s a carb model you still need this, as they standardised on parts and used the same fuel tank in all models.

If you have the wrong sender unit it will only rise so far, before it gets stuck and gives a low reading.

I have a 1989 mayfair. ordered the correct Sender at the time - http://www.minispare...c/XNB10007.aspx



#7 dangerousdowning

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Posted 11 November 2018 - 02:11 PM

OK, so shorting the 2 wires did cause the fuel gauge needle to full rise.

I found the small connector to be a be loose and on inspection it was partly damaged. So replaced that and it still didn't really improve - £20 of fuel and just out of the red.



#8 harrythehat

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Posted 11 November 2018 - 03:03 PM

confusus say old Chinese proverb "carry a can no run out of fuel"



#9 matt615

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Posted 11 November 2018 - 03:44 PM

OK, so shorting the 2 wires did cause the fuel gauge needle to full rise.
I found the small connector to be a be loose and on inspection it was partly damaged. So replaced that and it still didn't really improve - £20 of fuel and just out of the red.


Ok so definitely a problem with the sender unit.

The next test would be to remove the sender unit, and operate it by hand to the full position. If the gauge goes to full, you know it’s getting stuck on something in the tank. If not, then the sender unit is faulty.

Obviously you’ll need to make sure that the petrol is below the level of the sender unit before removing it.

#10 dangerousdowning

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Posted 11 November 2018 - 06:56 PM

 

OK, so shorting the 2 wires did cause the fuel gauge needle to full rise.
I found the small connector to be a be loose and on inspection it was partly damaged. So replaced that and it still didn't really improve - £20 of fuel and just out of the red.


Ok so definitely a problem with the sender unit.

The next test would be to remove the sender unit, and operate it by hand to the full position. If the gauge goes to full, you know it’s getting stuck on something in the tank. If not, then the sender unit is faulty.

Obviously you’ll need to make sure that the petrol is below the level of the sender unit before removing it.

 

 

I'd replaced the sender a few years back, when trying cure the problem....

But will remove it and try the manual test.



#11 Moke Spider

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Posted 11 November 2018 - 07:06 PM

confusus say old Chinese proverb "carry a can no run out of fuel"

 

Just be sure the battery terminals are covered (if you carry the can in the boot) and be sure to use it up and re-fill it every once in a while ;D



#12 matt615

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Posted 12 November 2018 - 06:13 AM

I did once have a similar problem after fitting a new sender unit. I think it must have got jammed on something when I fitted it. Removing and refitting it solved the problem.

Or perhaps someone has fitted a later type tank at some point?

Anyway the manual test will narrow it down.

#13 dangerousdowning

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Posted 16 December 2018 - 02:17 PM

Finally had some time to look into this further.

 

I took the sender out and carried out some tests.

 

With the sender out and the arm all the way to the 'full' point, the gauge reads just over 3/4 full (shorting the wires reads full).

 

With the sender in and some fuel in it, its pretty much reading empty.

 

Is there a 'reset' on the sender that can be done? With it out of the tank, I had it set to empty, then removed the terminals and put them back again. Also did the same with it moved to full, but made no difference. I also noticed a screw on it, so didn't know if this was some kind of adjustment?

This was a new sender...wondering if it was a duff one.  

 

http://s1239.photobu...n tank.png.html

 

http://s1239.photobu...f tank.png.html



#14 DeadSquare

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Posted 16 December 2018 - 02:37 PM

I don't know if you still can, but it used to be quite easy to take some senders apart.  Inside there is a resistance wire coiled round something like a memory card with a striker that wipes across it.  The striker is fixed to the arm of the float.

 

With the float pushed up to the full position, it was easy to see if the strike moved right to the top of the resistance coils and formed a short circuit;  and if it didn't, juggle the card and striker until it did.



#15 dangerousdowning

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Posted 16 December 2018 - 03:35 PM

The screw is the adjustment to the striker arm. turn too much and is goes too far and stops reading altogether. get it at the maximum and it still doesn't read a full tank.

Just need to rule out anything else, before I order yet another sender unit. 






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