Fuel gauge issues
Discussion
I'm sure ,it's something simple, but my fuel gauge has decided to show full all the time.
I've taken the sender out of the tank, there's 12v at the plug, and that varies as the float moves up and down. I measured the voltage at empty and it is about 5v, raise the float to full and it drops to 0.6v. At the gauge, there's 12.25v.
Ignition off and gauge drops to empty as you would expect, disconnect the plug on the sender and it drops, but more slowly to empty. Turn the ignition on when the gauge is dropping and the sender disconnected and it will show where it stops and not drop any further. For example, disconnect sender, turn ignition off, gauge drops. When it gets to half a tank, switch on ignition and it will register half a tank and stay there. Connect the sender and it will show full.
Is it the sender unit, the gauge or an earth somewhere between the gauge and sender? I'm guessing it's simply a resistance on the +ve that registers full to empty and the float moves? It doesn't look complicated.
For what it's worth, the sender unit looks brand new.
I've taken the sender out of the tank, there's 12v at the plug, and that varies as the float moves up and down. I measured the voltage at empty and it is about 5v, raise the float to full and it drops to 0.6v. At the gauge, there's 12.25v.
Ignition off and gauge drops to empty as you would expect, disconnect the plug on the sender and it drops, but more slowly to empty. Turn the ignition on when the gauge is dropping and the sender disconnected and it will show where it stops and not drop any further. For example, disconnect sender, turn ignition off, gauge drops. When it gets to half a tank, switch on ignition and it will register half a tank and stay there. Connect the sender and it will show full.
Is it the sender unit, the gauge or an earth somewhere between the gauge and sender? I'm guessing it's simply a resistance on the +ve that registers full to empty and the float moves? It doesn't look complicated.
For what it's worth, the sender unit looks brand new.
October.
And it was doing this when I picked it up. A jiggle of the connection on the sender seemed to fix it. Until this weekend. Now no amount if jiggling is changing the situation.
The sender isn't new. I can see the track where the arm has moved up and down the resistor.
And it was doing this when I picked it up. A jiggle of the connection on the sender seemed to fix it. Until this weekend. Now no amount if jiggling is changing the situation.
The sender isn't new. I can see the track where the arm has moved up and down the resistor.
Edited by Tyre Smoke on Monday 7th February 20:06
Update. Been out this morning with my multimeter.
The sender is faulty. The resistor has a broken wire, only the thickness of a hair. Also moving the earth wire on the sender started it 'working'. It now reads full to half accurately, but no lower than half because of the broken wire.
Finding it difficult to find a replacement, but I think this may work...
https://www.ebay.co.uk/itm/35cm-13-78-Fuel-Level-S...
The TVR tank is 370 deep and the float and sender combined on 'empty' seems to be 350mm
The sender is faulty. The resistor has a broken wire, only the thickness of a hair. Also moving the earth wire on the sender started it 'working'. It now reads full to half accurately, but no lower than half because of the broken wire.
Finding it difficult to find a replacement, but I think this may work...
https://www.ebay.co.uk/itm/35cm-13-78-Fuel-Level-S...
The TVR tank is 370 deep and the float and sender combined on 'empty' seems to be 350mm
Yes, that's exactly what I need, but it's out of stock.
From what I can tell, the sender unit is made by Smiths. It looks like a Landy 110 petrol sender except the TVR one has five unevenly spaced fixing holes and the Landy has six evenly spaced. It's even listed separately on Smiths website. Typical it being a TVR specific part!!
From what I can tell, the sender unit is made by Smiths. It looks like a Landy 110 petrol sender except the TVR one has five unevenly spaced fixing holes and the Landy has six evenly spaced. It's even listed separately on Smiths website. Typical it being a TVR specific part!!
Yep, I think it's a broken or partially broken sender wire. I'll do some diagnostic work tomorrow.
Found a useful site (for boats but the wiring is rhe same a a TVR) to crib from.
https://www.sailmagazine.com/diy/test-replace-fuel...
Found a useful site (for boats but the wiring is rhe same a a TVR) to crib from.
https://www.sailmagazine.com/diy/test-replace-fuel...
I've got 12v at the sender unit.
My tank is near empty, connect everything up and gauge reads full. Disconnect sender wire from gauge and gauge reads empty. Jump a wire from sender connector on the gauge to earth and gauge reads full. Disconnect earth on the gauge and gauge drops to empty. I'm beginning to think it's the gauge.
It was showing full when I bought the car in October and didn't move. I assumed because of lack of use the float had stuck or dry/corroded connection on the sender unit or elsewhere. Gave the connector on the sender a wiggle and the gauge worked fine for a few weeks. Last weekend and it's back to full all the time.
My tank is near empty, connect everything up and gauge reads full. Disconnect sender wire from gauge and gauge reads empty. Jump a wire from sender connector on the gauge to earth and gauge reads full. Disconnect earth on the gauge and gauge drops to empty. I'm beginning to think it's the gauge.
It was showing full when I bought the car in October and didn't move. I assumed because of lack of use the float had stuck or dry/corroded connection on the sender unit or elsewhere. Gave the connector on the sender a wiggle and the gauge worked fine for a few weeks. Last weekend and it's back to full all the time.
Yep, you're right. The sender works the opposite way to the original TVR one. My original was well worn and had frayed wires on the resistor.
The gauge shows full all the time, which as you say is effectively zero ohms. However, I've no apparent break in the sender wire, but I'll double check.
So I need to get a sender unit from Racing Green, because mine is definitely not well. I do think I can get it to work enough to confirm the gauge is dodgy though.
The gauge shows full all the time, which as you say is effectively zero ohms. However, I've no apparent break in the sender wire, but I'll double check.
So I need to get a sender unit from Racing Green, because mine is definitely not well. I do think I can get it to work enough to confirm the gauge is dodgy though.
I did sort if do that. Stuck my multimeter on ohms and read the sender unit. Original was goosed, well, ok to halfway, then a broken wire. The new one was great, 6 ohms empty, 190 ohms full. But we now know it should be 190 ohms empty, zero (or rhereabouts) full.
My gauge is reading either nothing or full all the time. And the wire between sender and gauge seems unbroken, but I do need to double check that.
Working on the basis that the TVR gauge reads the sender 'backwards' then grounding the sender wire should send the gauge to full (zero ohms) and disconnecting the sender wire from the gauge should send the gauge to empty (190 ohms - large resistance) Am I right? Logic tells me I am, but I did get a U in physics!! If the gauge read the sender at 190 ohms full, and 0 ohms empty (as I was expecting) then grounding the sender should show empty and removing the sender from the gauge should show full. I think.
My gauge is reading either nothing or full all the time. And the wire between sender and gauge seems unbroken, but I do need to double check that.
Working on the basis that the TVR gauge reads the sender 'backwards' then grounding the sender wire should send the gauge to full (zero ohms) and disconnecting the sender wire from the gauge should send the gauge to empty (190 ohms - large resistance) Am I right? Logic tells me I am, but I did get a U in physics!! If the gauge read the sender at 190 ohms full, and 0 ohms empty (as I was expecting) then grounding the sender should show empty and removing the sender from the gauge should show full. I think.
Nope!
I'm not giving up. I can do this. It's a simple wiring issue.
There are only three components. Gauge, sender, wiring. It's one of those. I've eliminated the sender, I will eliminate the gauge (and have a spare
) and then it must be the wiring.
I'll have it all back together and working perfectly by rhe weekend
I'm not giving up. I can do this. It's a simple wiring issue.
There are only three components. Gauge, sender, wiring. It's one of those. I've eliminated the sender, I will eliminate the gauge (and have a spare
) and then it must be the wiring.I'll have it all back together and working perfectly by rhe weekend
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