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Jun 14th, 2026
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Joined: Apr 2011
Posts: 8,646
Needs to Get Out More!
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Needs to Get Out More!
Joined: Apr 2011
Posts: 8,646 |
I found it unsettling when my 4/4 was managing to run on negative petrol according to the petrol gauge, the needle showing less than zero. Reminded me of Homer Simpson's reaction to Lisa's perpetual motion machine....... https://www.youtube.com/watch?v=gOMibx876A4
Giles. Mogless in Paris.
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Joined: Apr 2012
Posts: 5,013 Likes: 32
Charter Member
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Charter Member
Joined: Apr 2012
Posts: 5,013 Likes: 32 |
The fuel gauge on my 8 has never worked properly. It moves all over the place and is currently showing empty, with a warning light, despite having just filled it up.
I was told that Morgan use a unit from a marine engine - I wouldn't want to be at sea with no clue as to how much fuel was left.
+8 4.8
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Joined: Feb 2016
Posts: 8,667 Likes: 408
Needs to Get Out More!
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Needs to Get Out More!
Joined: Feb 2016
Posts: 8,667 Likes: 408 |
Does the sender earth through the screws from its cover plate or is there a separate earth connection? I have got a 2013 wiring diagram, albeit only A4 size so you need a magnifying glass. The sender appears from the parts book (V.5.2 - Fuel System Right - P.26) to be integral with the pump - part ref #6 unless it is what they describe as the "fuel tank dip pipe" - part reference #10 and this page shows the wiring (P.69 top right corner).
Wilson
No the sender on the M3W is separate from the pump although there was one integral to the pump for use on other applications such as Land Rover. The earth connection to sender is a tag in wiring loom which connects to the senders body via one of its mount bolts as you suggest. Picture here of 280mm sender with 750 ohm shunt resistor fitted.  This gave the best results for me although there were still random fluctuations. Generally I only got a consistent 0% gauge indication after at least 200 miles with plenty of reserve.
Richard
2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone
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Joined: May 2012
Posts: 1,796 Likes: 5
Talk Morgan Enthusiast
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Talk Morgan Enthusiast
Joined: May 2012
Posts: 1,796 Likes: 5 |
Mine must have come out in sympathy with yours.
If I brim the tank so I can see the fuel in the filler neck it only reads 84%, then after 50-60 miles it's down to 0%.
Just something else to fiddle with.
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Joined: Jun 2015
Posts: 580 Likes: 2
Talk Morgan Regular
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OP
Talk Morgan Regular
Joined: Jun 2015
Posts: 580 Likes: 2 |
The fuel gauge sending unit is a variable resistor.
Pull the sending unit, and remove the outer tube.
Inside are two parallel wires with a wiper on a float that connects the two wire. These wires oxidize and will create an intermittent connection.
Use some very fine sandpaper and gently wipe down each wire where the wiper makes contact with the wires.
I had the same problem and the fix was as describe above. The displayed level no longer jumps around... but I use the fuel gauge as a low I.Q. suggestion. When I get to 200 miles on the odometer, I fill up. Thanks for the tip. I will have a go at that. Somewhere I have some 6000/8000/10000 grade wet and dry paper, which I use for smoothing off scratchy fountain pen nibs. Now if I can only remember where I put it away, ever so carefully. Wilson
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Joined: Dec 2012
Posts: 54
Just Getting Started
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Just Getting Started
Joined: Dec 2012
Posts: 54 |
You need to buy a longer sender which costs around £60, fitted it myself in 30 minutes (and I am not very technical) and now I get an accurate reading every time
Morgan 3 Wheeler New Sport Green & Chrome, First Morgan was a 4 seater 4/4 in 1968
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Joined: Jun 2015
Posts: 580 Likes: 2
Talk Morgan Regular
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OP
Talk Morgan Regular
Joined: Jun 2015
Posts: 580 Likes: 2 |
No the sender on the M3W is separate from the pump although there was one integral to the pump for use on other applications such as Land Rover. The earth connection to sender is a tag in wiring loom which connects to the senders body via one of its mount bolts as you suggest. Picture here of 280mm sender with 750 ohm shunt resistor fitted. This gave the best results for me although there were still random fluctuations. Generally I only got a consistent 0% gauge indication after at least 200 miles with plenty of reserve. What is the purpose of the shunt resistor? I could certainly understand a shunt capacitor to remove any stray AC. I can easily order a 750Ω resistor. I have a wonderful case of tennis elbow on my right arm at the moment and was not looking forward to removing all those screws on the boot liner. However, I have now treated myself to a Milwaukee 1/4" cordless ratchet and a set of 1/4" square drive screwdriver bits (I already have a large set of 1/4" sockets, metric and AF), so it will now be very easy. I also have to take the pedal box cover off as well, to replace the worn out friction coating on the clutch pedal with glued on emery cloth, where the Milwaukee will be perfect. Wilson
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Joined: Feb 2016
Posts: 8,667 Likes: 408
Needs to Get Out More!
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Needs to Get Out More!
Joined: Feb 2016
Posts: 8,667 Likes: 408 |
What is the purpose of the shunt resistor? I could certainly understand a shunt capacitor to remove any stray AC. I can easily order a 750Ω resistor. I have a wonderful case of tennis elbow on my right arm at the moment and was not looking forward to removing all those screws on the boot liner. However, I have now treated myself to a Milwaukee 1/4" cordless ratchet and a set of 1/4" square drive screwdriver bits (I already have a large set of 1/4" sockets, metric and AF), so it will now be very easy. I also have to take the pedal box cover off as well, to replace the worn out friction coating on the clutch pedal with glued on emery cloth, where the Milwaukee will be perfect.
Wilson
Simply to lower the resistance measured by the display circuitry. In this case it changes the range to give more sensitivity at lower fuel levels which is where you need it. Downside was that gauge indicated 100% for first 20-30 miles from full tank. Remember this mod was in conjunction with the longer sender though.
Richard
2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone
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Joined: Mar 2015
Posts: 902
Talk Morgan Regular
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Talk Morgan Regular
Joined: Mar 2015
Posts: 902 |
What wattage for the resistor?
John.
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Joined: Feb 2016
Posts: 8,667 Likes: 408
Needs to Get Out More!
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Needs to Get Out More!
Joined: Feb 2016
Posts: 8,667 Likes: 408 |
Not critical as it's a high impedance circuit so minimal current. I think mine was 0.5 watt.
Richard
2018 Roadster 3.7
1966 Land Rover S2a 88
2024 Royal Enfield Guerrilla 450
1945 Guzzi Airone
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