Fuel and Temp guage reading too high from cold on a TR7

[Vin]

Hi, hope you can help me to find out the last couple of niggles on this TR7. Its been laid up for over 10 years and I helped to get it MOT ready.
I found new light switches, new alternator, new fuses, cleaning up of the connections under the centre speaker by the dash helped correct electrical problems. At first only one light would work, no indicators etc After I managed to get all the lights working. Now the electrics are behaving them selves but I have a problem with the smiths temp guage and fuel guage.

With the fuel guage I had to take the dash apart and move the needle, the guage came back into life but I know it has a 55 litre tank. I put 8 litres and then 10 litres from the pump which should be less than half of the tank but the guage reads near three quarters??

The temp guage, i fitted a new engine sensor as soon as switching the car on, the temp guage starts to climb. Even if the car has been standing for over 24hours. Once switched on the guage reads over a quarter. Then when its started the temp guage seems to sweep up easily. ?

Any ideas? Thanks in advance. Vinny

[Hawkshaw]

Voltage stabiliser?

[Vin]

Thanks for that suggestion although I think the TR7 did not have any fitted. The only thing I could find was a low voltage relay which works with the low fuel light.

I did find the voltage delay relay which works on the low fuel gauge. It apparently helps to stop the fuel light flashing. I disconnected all wires to this and it made no difference on the clock readings?

Vin

[mike9009]

Earth points all clean??

[Vin]

Thanks, I ran a additional earth from the chassis to the clocks. Plus I checked the voltage was the same as the battery?
Vinny

[oakdale]

Someone else who had the same problem and solved it.

https://www.triumphexp.com/forum/tr7-and-tr8-forum...

[Vin]

Thanks, i will give that another go, I did check that the earths were good on the back of the clocks. It might be worth running additional earths just in case.
Vinny
I will let you know if it works or not

[Vin]

Oakdale, thanks for pointing out that link. I ran an additional earth to both of the switches. I could not take the flexible strip from the clocks as they do not make this part any more. I think either i have to try new temp or fuel guage or run wires to cut out the existing wiring. I can only think these are at fault causing higher resistance as when I start the car, the needle moves to a quarter, then off the scale within a few seconds.
Vinny

[simontdo]

If it's been stood for that long the fuel sender is probably rusted and seized.

It's quite easy to remove from the tank and have a look. You could even short the wires out at the tank and see if you can get it to go to full?

The temp guage is odd. Have you checked the engine earth?

[Vin]

Thanks for the ideas, I think that i have supplied good earths as I used a fluke meter to calibrate the voltage at the clocks. It seems I am getting the nearly the same voltage as the battery. The earth seems good and now I have run a earth to each of the clocks and to earth. Its only the temp guage and the fuel guage that seem to run very high. Also on starting up within a few seconds the temp guage goes off the scale. This does not match the hoses which are luke warm and cold. I can only think that after 20 odd years of standing the guages or wiring has gone off, maybe high resistance?
I am thinking now to try some new guages in place of these although they do not sell them any more so i will have to find alternative guages.
Vinny

[singlecoil]

Vin said:

I am thinking now to try some new gauges in place of these although they do not sell them any more so i will have to find alternative gauges.

Try these people

https://speedycables.com/

back when I was involved with TR7s they were able to covert my rev counter to work with the V8 I fitted.

[Vin]

thanks for that link. I have sent them a email and await a reply

[droopsnoot]

Surely if the wiring had gone high resistance, it would lead to lower readings rather than higher? And surely you would be able to measure that?

Do these gauges work the same way as my seventies Vauxhall ones do? Basically a voltmeter, with a steady 12v supply from the ignition circuit and a the sensor / sender unit providing a variable resistance to earth? If they do, the gauges reading high would suggest that they're getting too much earth, perhaps because of a short somewhere.

Can you easily run a wire from the gauge to the sender unit, by-passing the loom? Or perhaps measure the resistance between the sender unit and earth with your meter, and see how it changes when the temp or fuel level changes?

In theory you could use your meter in the same way to eliminate things. Connect the positive probe to battery + and the negative to the temperature sender unit, observe the reading in volts, which will probably be close to zero (because when cold, the temp sender has a high resistance). Then start the engine and warm it up, and you should see that the voltage reading increases as the temperature rises, because the resistance in the sender unit is decreasing. If that operates as it should, move the negative meter probe to the end of the wiring loom where it joins to the dash and do the same test. If that works in the same way, then in theory your sender and loom are good, and the problem is in the gauge or dash. The same test can be done on the fuel gauge circuit, but it's more hassle to be adding fuel.

You also mentioned that you'd moved the needle on one gauge, not sure what you meant by that.

It's also worth checking entirely unrelated earths, I've had situations before now where a bad earth in one circuit can cause all sorts of weird and wonderful symptoms in others.

If the car has been standing for a while, you can get corrosion on the internals of the fuel sender unit, which can cause problems with the reading.

Edited by droopsnoot on Thursday 24th June 09:52

Edited by droopsnoot on Thursday 24th June 09:53

[Vin]

Thanks for your help and tips. Ken has his car (TR7) back now and will use it a little. I will near the end of the season when the car is put away have another look, as you say investigate the wiring and readings at various stages.
re the fuel guage, this would not work at first until i took apart the dash, moved the fuel needle which had stuck on empty. It now works but is a high reading, saying that there is three quarters of tank. That is not much of a problem. Its more the temp guage that i would have liked to find out why its so temperamental with readings. To have fixed that.
Thanks again Vinny

[Vin]

Some more work on the Tr7
I have replaced the sender, checked this when warm and cold and can see a difference in ohms resistance.
I have removed the clocks and with the ignition off can get a ohms resistance on the terminals of the temp guage.
The original guage when connected went off the scale as soon as connected.
I managed to get a second hand guage, when i compared the new guage to the old one. The original one had open circuit on one side, there are three terminals on the back, one i see is earth and the other two are 12v supply and i read a 4v supply. I assume the 4v is the reduced resistance to move the guage over.
I thought i had found the issue with the guage having different readings and open circut. Checked the new second hand one and it had resistance readings 160ohms and 60ohms from the terminals to earth.

Put the guage in and no readings at all. I am stumped as i am getting ressitance readings and voltage at the terminals. I wonder if the plastic film on the back is faulty in some way. I am not sure what to do now other than fit a alternative guage?

Thanks in advance. If you have any suggestions i can try. Vin

[Vin]

Success i hope, i ran a new wire from the sender to the dash. The ohm reading was 210. I then checked the original and it was 45ohm. I can only guess as i keep taking the dash out, move wires etc.
Now i have a reading on the guage if add this additional wire. i hope this helps you out. My learning is to take time and take ohm readings, check again, check again.

[droopsnoot]

Vin said:

I wonder if the plastic film on the back is faulty in some way.

I have had similar on my Vauxhall - the dash lamps and voltage regulator clip into the plastic structure of the dash and trap the contact from the plastic circuit against the contacts, and some of them had broken of due to becoming brittle over the years. I have almost no dash lighting on one of the cars because of this issue. Not sure if you could get a replacement for yours with it being a Triumph and decent parts supply - I had to make mine.

[Vin]

Fixed the issue
It was the resistance of the wirring. I ran an additional wire from the sender directly to the back of the temperature gauge and it worked.
The guage was also faulty.

Vin thanks for your help and suggestions