Fuel gauge adjustment

[nickw71]

Hi all from sunny (and cold) Madrid,

 

Does anyone know if there is any way of adjusting the fuel gauge (CP model)?

 

Mine reads 1/8 - 1/4 fuel when empty and goes way off the scale with a full tank.

 

I´ve checked the Brown Book, nothing, and trawled the forum and internet with no luck.

 

I think my car has a recent sender unit fitted and as the temp gauge appears to be working correctly I think I´m right in assuming the voltage stabaliser isn´t at fault.

 

Is there anything in the gauge itself that sets the start and end of the needle travel?

 

Nick

[peejay4A]

Tank senders seem to be of variable quality, and variable resistance (no pun intended).

 

Is the tank really empty when you get your 1/8 - 1/4 reading? If it is then the float might be bottoming out in the tank, can you see it with a torch?

 

If so you'll need to remove the sender and bend the operating arm so as to move the float upwards a bit in relation to the bottom of the tank. It'll be a bit hit and miss though. If you remove the filler cap to tank pipe and slacken the tank mounting bolts you may be able to swing the tank back far enough to do the job without removing it completely although I can't remember if the fuel return pipe limits movement. As you get a way over max reading when full this would be my bet.

 

If the float isn't bottoming out then your problem is a little more complex. I found I couldn't get maximum resistance (equivalent to empty) from my replacement sender so I had to adjust the end stop to allow the wiper to use more of the resistance coil. Another fiddly job as you have to ensure that the wiper doesn't leave the resistance coil completely and get stuck.

Edited November 12, 2012 by peejay4A

[peterq]

Hello Nick,

 

I had the same problem, just the other way around, fuel gauge showing too low.

 

First check if 10 V arrive at the sender by removing the coloured wire and measuring it to earth. This should be 10 V coming from the stabilizer. If you measure 12 V then the stabilizer is the problem.

 

Next would be removing the tank and taking the sender out. Move the float up and down to check the output on your gauge, it takes a little time to react. On the outside of the sender there is a small pin with a slot, this is to adjust the sender. Just turn it one click and see what happens. I cannot remember which way around you have to adjust it. After adjusting I checked the resistance, max to min position was 20.8 to 200 Ohms.

 

After adjusting it shows quite accurate!

 

Good luck, Peter.

 

 

[peejay4A]

Interesting. There was no adjuster on my sender so I had to resort to judicious bending.

[peterq]

Hi Pete,

 

Possibly you worked on a TR4 sender, they are different from TR6. The Moss catalogue shows TR4 senders are not available anymore and replaced by TR6 senders.

 

Peter.

[peejay4A]

Possible. I bought the sender and universal fitting tank over a year ago so I don't know the part number. The sender was UK made as I recall and of very crude and flimsy construction.

[nickw71]

Hi Peejay4a & Peter,

 

Thanks for the replies. Both very useful. I´m definatley out of fuel when the needle is between 1/8 and 1/4 full as we´ve been caught out a couple of times.

I better do a check on the stabiliser as it´s a two minute job and and a tenner replacement if it´s that.

If not the stabiliser it look like it´s a case of removing the sender unit and either using the adjuster or if it´s not present then bending the float rod! Thanks for the Ohms reading. Those figures correspond with something a US TR owner has on his website.

 

Changing tack; do either of you have any experience with the oil pressure guage. I´ve just replaced my dashboard back to original spec hence the gauges have been out of the car. Now the oil pressure guage is stuck at 50lbs. At first it stuck at 5lbs and then jumped to 50 and remains there with the engine off.

 

Do you need to bleed the oil feed tube before reconnecting it to the back of the gauge?

 

Regards,

 

Nick

[peejay4A]

Nick,

There's no need to bleed the oil feed to the gauge. It sounds as though the link from the bourdon tube to the needle is sticking. If you're brave you might disassemble it and take a look inside. A lube with some watch oil (available on ebay) might do the trick. Otherwise Speedy Cables do an excellent refurbishing job although at a price. Other refurbishers are available.

[peterq]

Hi Nick,

 

I removed the oil feed tube as I took the engine out. Connected afterwards without bleeding. No problem. So I assume your instrument has a problem. Probably cheapest is to buy one on Ebay.

 

Regards, Peter.

[cvtrian]

Do you need to bleed the oil feed tube before reconnecting it to the back of the gauge?

 

Regards,

 

Nick

 

Hi Nick

I did have quite a few issues with variable oil pressure readings (as opposed to stuck) after I had disconnected the oil pressure gauge on my TR3A (same engine), and bleeding the pipe by slackening off the gauge connection whilst the engine was running (obviously making sure the oil was contained by wrapping a rag around the pipe/nut), - problem solved.

So I would say yes - cheapest and easiest first, bleed the pipe first before anything else, air is compressible, oil not.

Good luck

Cheers

Ian

[peejay4A]

If the needle is stuck with the engine off then bleeding won't help.

[Grabea]

And anyway pressure is the same whether it's air pressure, oil pressure or any other medium.

Graham

[Richard Green 54]

Due to the lockdown I have managed to do less than 200 miles since buying my 1975 TR6 in January. But I have still managed to run out of fuel with the gauge showing 1/4 full. Fortunately I had a 5L can of fuel in the boot. When I reached the nearest garage and filled it up the needle was off the top of the gauge. So the same problem as in Nick's original post.

I checked the voltage at the sender and it was reading 11.8v. So I assume  the voltage regulator is not working properly. However the temperature gauge, running off the same VR, seems to be reading perfectly, so I am a bit confused.

Anyone have any ideas as what might be wrong?

[Mike C]

I'd check the electrical connections to the fuel gauge, if they look OK , I'd have a look at the sender in the tank.

[ed_h]

A steady 11.8 volts at the sender suggests a bad stabilizer.  I'd fix that first.

For a stock stabilizer, a voltage oscillating between 12 volts and 0 volts once or twice a second is normal.

For an aftermarket solid state stabilizer, the reading should be a steady 10 volts.

Ed

Edited April 11, 2020 by ed_h

[Richard Green 54]

4 hours ago, ed_h said:

A steady 11.8 volts at the sender suggests a bad stabilizer.  I'd fix that first.

For a stock stabilizer, a voltage oscillating between 12 volts and 0 volts once or twice a second is normal.

For an aftermarket solid state stabilizer, the reading should be a steady 10 volts.

Ed

I agree Ed and have already ordered a solid state voltage stabiliser. That should fix the fuel gauge problem but I am a bit worried about the effect it will have on the temperature gauge. Although it could be that an over reading temp gauge is masking another problem such as a radiator thermostat jammed open. Guess I will find out in due course.

[DaveR]

3 minutes ago, Richard Green 54 said:

I agree Ed and have already ordered a solid state voltage stabiliser. That should fix the fuel gauge problem but I am a bit worried about the effect it will have on the temperature gauge. Although it could be that an over reading temp gauge is masking another problem such as a radiator thermostat jammed open. Guess I will find out in due course.

Or it could be the temp sender is the problem.

Dave

[astontr6]

35 minutes ago, Richard Green 54 said:

I agree Ed and have already ordered a solid state voltage stabiliser. That should fix the fuel gauge problem but I am a bit worried about the effect it will have on the temperature gauge. Although it could be that an over reading temp gauge is masking another problem such as a radiator thermostat jammed open. Guess I will find out in due course.

I had problems with my water temp gauge and it turned out to be the gauge and sender unit. An MGB owner pointed me in the right direction by telling me to go to a company in Wales called Caerbont Automotive Instruments : Tel:01639 732200. They make all the TR series instruments off the original tooling so, you are replacing like with like! Moss's sender units don't work properly with Smiths instruments, the reading will be all over the place?. They also make the proper speedo gear box cable drive which does not fail after a few hundred miles? This is where Speedy Cables get all their Smiths instruments spares from.

Bruce.

[RobH]

Just now, astontr6 said:

Moss's sender units don't work properly with Smiths instruments, the reading will be all over the place?.

That may be because there are a number of different senders and you have to get the one with the resistance/temperature characteristic which matches your particular gauge type. 

[Richard Green 54]

At the moment the fuel sender works but just reads high. What I do know is that the supply voltage at the tank is wrong. So for the sake of £10 I am following Ed's advice and replacing the VS with something that works properly and is a bit more reliable. If that does not work I will probably end up bending the float arm on the sender unit. If that does not work I will invest in a wooden stick with some notches cut in it.

[DaveR]

Be careful not to short the output of the stabiliser to ground as they are not all short circuit protected.

Dave

[astontr6]

1 hour ago, RobH said:

That may be because there are a number of different senders and you have to get the one with the resistance/temperature characteristic which matches your particular gauge type. 

You are right as I had to read the smiths part number off the original to confirm that I was getting the right one. They indicated that there were about 40 different types that they made?

Bruce.

[Richard Green 54]

In the end that turned out to be a simple fix and was all down to me mixing up two green wires behind the dash. Feed to the heater fan switch swapped with the feed to the fuel gauge. My punishment was having to take the dash out again. Never mind it's all good practice and got me out in the sunshine for an hour or so.