Fuel Gauge and sender issue

[Jt850]

I've read heaps of posts and info on www but can't find an answer to this, so hopping someone here can help.
I have a new speedo head that came with new gauge and voltage stabilizer. The gauge never went above 3/4 full mark (actually just below it). Checked the gauge by earthing the sender and gauge went to full. So went and bought a new sender! Hooked it up before pulling out the old one and bugger me, it still only reads to 3/4 when float is in the full position. So checked the ohms, it was wildly off 270 empty and 33 ohms when in full position. Adjust it to read 222 on empty and 20 on full. Gauge still reads well under full. Adjusted it again but had to drop it to about 7ohms before I could get a full reading on the gauge. Why is this so? Is this going to be a problem? Could it harm the gauge? Thanks for any advice.

[dklawson]

I cannot say why the gauge and sender are not preset to cover the necessary range. However, it may be an aftermarket part which was incorrectly adjusted.

Succinctly, tweaking the range of the sending unit so "empty" occurs at 220 Ohms is not going to change how the gauge reads. The needle is still going to fall where it did before... at 220 Ohms.

It sounds like instead what you should do is re-adjust the stop tabs on the sender so empty is about 270 Ohms and full is about 33 Ohms. Then, working at the bench with a 10V power supply, re-calibrate the gauge to match the sending unit. Re-adjusting the gauge is not a quick process and it is not well documented on the web. I had a couple of links bookmarked but can only find the one provided below. I hope it helps. (NOTE: The resistance range discussed in the article linked below is for an MGB. For your Mini you need/want 270 to 33 Ohms).

http://www.chicagolandmgclub.com/techti ... e_cal.html

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

And one more...
https://www.triumphexp.com/forum/triump ... l.1405143/


EDIT: I almost forgot, there is another option for your situation. You can buy a "Gauge Wizard" offered by Spiyda Design. It will allow you to match and calibrate your sending unit to your gauge... as is. Though it is more money, it should allow you to address the problem with ease.

[Spider]

Some of the Fuel Tanks have a longer neck that goes down a way inside the tank. I've had some senders foul on the neck and so not letting them float all the way up when full.

It's not easy to accurately check for this, one way is when the fuel level is low, remove the sender, put some light string down through the filler and fish it out through the sender hole, then tie it to the sender arm(close to the sender maybe best) and refit it all, then by gently pulling on the string you should be able to observe the action of the arm.

[Jt850]

I cannot say why the gauge and sender are not preset to cover the necessary range. However, it may be an aftermarket part which was incorrectly adjusted.

Succinctly, tweaking the range of the sending unit so "empty" occurs at 220 Ohms is not going to change how the gauge reads. The needle is still going to fall where it did before... at 220 Ohms.

It sounds like instead what you should do is re-adjust the stop tabs on the sender so empty is about 270 Ohms and full is about 33 Ohms. Then, working at the bench with a 10V power supply, re-calibrate the gauge to match the sending unit. Re-adjusting the gauge is not a quick process and it is not well documented on the web. I had a couple of links bookmarked but can only find the one provided below. I hope it helps. (NOTE: The resistance range discussed in the article linked below is for an MGB. For your Mini you need/want 270 to 33 Ohms).

http://www.chicagolandmgclub.com/techti ... e_cal.html

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

And one more...
https://www.triumphexp.com/forum/triump ... l.1405143/


EDIT: I almost forgot, there is another option for your situation. You can buy a "Gauge Wizard" offered by Spiyda Design. It will allow you to match and calibrate your sending unit to your gauge... as is. Though it is more money, it should allow you to address the problem with ease.

Yep, I’ve been adjusting the tab stops on the sender to get those readings, although one link I had gave me the settings as 222 for empty. So the sender as I received it at 270 and 33 would be correct then. So it seems then that the issue must be with the new gauge. I will check out the link on adjusting the gauge, thanks very much for all the info too.

[Jt850]

Some of the Fuel Tanks have a longer neck that goes down a way inside the tank. I've had some senders foul on the neck and so not letting them float all the way up when full.

It's not easy to accurately check for this, one way is when the fuel level is low, remove the sender, put some light string down through the filler and fish it out through the sender hole, then tie it to the sender arm(close to the sender maybe best) and refit it all, then by gently pulling on the string you should be able to observe the action of the arm.

I did a similar process to that but after finding that the arm was fully up and gauge still not reading full, led to believe the problem was with the sender, hence buying a new one. Thanks though for your thoughts.

[Spider]

Some of the Fuel Tanks have a longer neck that goes down a way inside the tank. I've had some senders foul on the neck and so not letting them float all the way up when full.

It's not easy to accurately check for this, one way is when the fuel level is low, remove the sender, put some light string down through the filler and fish it out through the sender hole, then tie it to the sender arm(close to the sender maybe best) and refit it all, then by gently pulling on the string you should be able to observe the action of the arm.

I did a similar process to that but after finding that the arm was fully up and gauge still not reading full, led to believe the problem was with the sender, hence buying a new one. Thanks though for your thoughts.

Ok sure, no problem, that base is covered.

I have read widely varying resistance figures for the fuel tank senders over the years and probably like you, wasn't sure just what to follow.

Smiths kindly provided me with that info. Full should be 33 ohms. Empty should be 240 ohms.

Bending the stop tab is not always wise as you can get the resistances you are looking for out of the tank, but when fitted to the tank, the float can (and usually does) hit the top and / or bottom of the tank before coming to the stops.

The Sender is adjustable. I really don't like steering traffic away from this forum however I did a write up on adjusting the Sender and the Gauge here;-

http://www.theminiforum.co.uk/forums/to ... el-gauges/

[Jt850]

Thanks Spider that is great! Just checked everything right through from the sender to the gauge, just to make sure the mini's wiring wasn't creating increased resistance somewhere, but it's all good - reads same resistance at the gauge as at the sender.

So anyone want to buy a mini? I'm over it today!!!
Got it adjusted as per your great instructions thanks Spider, went and bought the resistors and set it all up. Did manage to get it reading a little higher, but that only seems to adjust the position of the needle not the actual sensitive of the gauge, if that makes sense. The gauge will not move to full with anything greater than about 8 ohms. At adjustment for a full reading at 30 ohms puts the needle at rest (or off) sitting at 1/4 empty. So as you explain, it's a balancing act of getting it reading right at all ohms, but that was impossible. This gauge won't do it. So I'm figuring the new gauge is faulty, so I'll just put up with it (and have a spare sender unit!). Then I spent the rest of the day putting it all back together again, right pain, only to fire it up and the temp gauge is now not working - goes straight to high (I wish the fuel gauge would do that!). So more hours pulling it all apart again and trouble shooting the temp gauge. Seems the old Pricol gauge is at fault. Something wrong inside - if I move it about, it will drop then go to high etc. But why did it go just because I pulled the fuel gauge out? Bloody, bloody, bloody Murphy at it again I reckon.

[Polarsilver]

JT .. IF this is of any help i have two used Smiths original Fuel Gauges with Black Face ( BF6108/00 MM1 Made in UK ) .. that you are welcome to have both for your trials .. perhaps you can solve your problems with an original Gauge pm to me with your address.

[Spider]

It really does sound like a duff gauge !

[Jt850]

Fixed the temp sender today, yay! Turned out in my frustration with the fuel gauge I did't connect the earth lead to the temp gauge and it was trying to earth through the bulb holder! My bad!

Fitted the new sender after testing it out of the tank and still reading just over 3/4 full. Fitted in the car and now doesn't read just over empty. Thought I might have knocked the float off when installing it, but no, full tank and I can see the sender arm floating on top.

Fortunately Polarsilver here has very generously and considerately offered to send me a couple of fuel gauges to try and get it sorted, so I'll wait till they arrive before going any further. Thanks everyone for all your help, been much appreciated.

[111Robin]

What a hassle. You said this is a new speedo head with fuel gauge, is it genuine nos or reproduction ?. I have a Smith's instrument tester that checks the gauge at empty, half and full, if you want to send the gauge to me I can check it out. I always use this to eliminate the gauge (fuel or temperature) from the equation.

20141017_171038 by Robin Derrick, on Flickr

[Polarsilver]

111Robin ... i intend to send out to John in Australia two used & untested Smiths Fuel Gauges .. it would be good if i can send them up to you for testing before they ship as they are not a lot of use if they are knackered .. i will send you a pm to see if you can agree to this suggestion.

[111Robin]

111Robin ... i intend to send out to John in Australia two used & untested Smiths Fuel Gauges .. it would be good if i can send them up to you for testing before they ship as they are not a lot of use if they are knackered .. i will send you a pm to see if you can agree to this suggestion.

No problem at all, I have replied to your PM

[Jt850]

Can't thank you enough fellas! Much appreciated.