Fuel sender test ?

[W.olly]

Hi all.
One thing i would like tonwork again on my Vette. For obvious reasons haha.
The fuel gauge has stopped working and showing over full all the time.
Now I have checked the earths and all good.
Now before I remove the cluster of gauges to check the gauge itself I am going to check the sender.
And before I remove the sender I was wonder if this will tell me if the sender has failed?

It is showing nothing on the Ohms when I connect the meter to the sender connectors.

Am I correct in thinking that it should show a reading. The more the tank is full ?
It's showing this at the minute.

Just trying to see if i can move the float to see if the readings change. . Bit tight though.

 

[dobbslc]

I think you should be able to find the correct reading online for empty and full and see how it compares.
Don't send 12v down the wires though just incase it all goes pufff.

 

[sako243]

Change the range on the meter to 200 ohms. Most senders I've seen are in the <1k range (quite often 10-300R between full and empty).

Try and change the float and see if it changes.

 

[W.olly]

I think you should be able to find the correct reading online for empty and full and see how it compares.
Don't send 12v down the wires though just incase it all goes pufff.

I found the readings for it. They are between 0 - 90 Ohms. I added 4 gallons to it and it takes 24 gallons. So maybe not far off.

Change the range on the meter to 200 ohms. Most senders I've seen are in the <1k range (quite often 10-300R between full and empty).

Try and change the float and see if it changes.

On 200ohms it shows this.

Are we saying the sender is good then.

Hope so as I rather sort he gauge out. Need other bits to do here you see.

 

[sako243]

If you can move it a bit by adding some more or draining some off then I'd say so.

It's likely good though but getting it to move from full to empty would confirm it.

 

[ajlelectronics]

Test from the other end. Take the tank connection off and ground it. Gauge should now show FSD. If it doesn't, ground the sender wire at the gauge and try again. That will diagnose the gauge and wiring as far as the tank.

 

[W.olly]

Change the range on the meter to 200 ohms. Most senders I've seen are in the <1k range (quite often 10-300R between full and empty).

Try and change the float and see if it changes.

If you can move it a bit by adding some more or draining some off then I'd say so.

It's likely good though but getting it to move from full to empty would confirm it.

I am filling this weekend so ill check it again.

Thanks all for the help

 

[Nomad]

I ran my current car (BL finest from the 1970s) for 3 years with no fuel gauge. Fill the tank to the brim before a long journey and track mileage.. eventually I fixed it by removing the sender unit and free-ing the seized float arm.

For a quick test, remove the wire from the tank sender and earth it.
Turn on the ignition and see if the fuel gauge moves towards "Full Tank" :
If the gauge moves turn ignition off asap so the gauge doesn't reach "Full" (and try to go past !).
If the gauge stays at empty the problem is the wiring from the tank to the gauge, not the actual gauge.

 

[ajlelectronics]

I ran my current car (BL finest from the 1970s) for 3 years with no fuel gauge. Fill the tank to the brim before a long journey and track mileage.. eventually I fixed it by removing the sender unit and free-ing the seized float arm.

For a quick test, remove the wire from the tank sender and earth it.
Turn on the ignition and see if the fuel gauge moves towards "Full Tank" :
If the gauge moves turn ignition off asap so the gauge doesn't reach "Full" (and try to go past !).
If the gauge stays at empty the problem is the wiring from the tank to the gauge, not the actual gauge.

There's an echo in 'ere.

 

[W.olly]

Today i put in £50 of loopy juice and the Ohms reading didnt change, staid on 35ohms.

So does this mean the sender is faulty as the Ohms on the earth and live out doe snot change ?

ill try Nomads suggestion and other tomorrow once we have been out for a bite to eat as i just want to go for a cruise.

Hey first time i been out with T tops off

 

[W.olly]

Just an update.

I removed the sender and its was intermitent ont he bench test. So i ordered a new one. aswell as a few other bits for it. BUT in the time i have to wait for the parts from America. all for the emblems i want for when i respray it. And i cant wait three week in nor driving the car.
So i refitted the old sender and it now sort of works. it has a 103l tank. i added £50 to a 1/4 tank and its now full. so its not to accurate.

 

[Migmac]

You’ll just need to remember that the only thing you can’t pass is a filling station, no need for a fuel gauge

 

[Nomad]

The gauge on my latest "barn find" was frozen at 1/4 tank.
When I pulled the sender the float arm had light fur on the pivot, cleaning and refitting has cured it.

My next problem is the yellow low fuel idiot light never comes on as the float switch on the sender unit is frozen.
Any ideas where I can buy or rob a switch (it's a simple tube with a float inside, on/off so anything can be made to fit. I'm looking at another project car I have and am considering taking the switch from that but it seems a shame..) scrapyards here are not helpful and I'd rather not pay for a "good used honest guv" tank in the hope the switch inside works..

 

[W.olly]

The gauge on my latest "barn find" was frozen at 1/4 tank.
When I pulled the sender the float arm had light fur on the pivot, cleaning and refitting has cured it.

My next problem is the yellow low fuel idiot light never comes on as the float switch on the sender unit is frozen.
Any ideas where I can buy or rob a switch (it's a simple tube with a float inside, on/off so anything can be made to fit. I'm looking at another project car I have and am considering taking the switch from that but it seems a shame..) scrapyards here are not helpful and I'd rather not pay for a "good used honest guv" tank in the hope the switch inside works..

what have you got for your project ?

Once i had a similar problem with a project. The sender was crazy money so as it was just a pick up tube with a sender attached, i got another sender and and cut the old one off and attached, ( Tig welded, but you could use a good metal putty or epoxy ) to attach the new one once its cut to length. You may need to bend it or shape the new pick up depending on what its like but it saved me a lot of hassle and money doing this. and worked well.

 

[ajlelectronics]

The gauge on my latest "barn find" was frozen at 1/4 tank.
When I pulled the sender the float arm had light fur on the pivot, cleaning and refitting has cured it.

My next problem is the yellow low fuel idiot light never comes on as the float switch on the sender unit is frozen.
Any ideas where I can buy or rob a switch (it's a simple tube with a float inside, on/off so anything can be made to fit. I'm looking at another project car I have and am considering taking the switch from that but it seems a shame..) scrapyards here are not helpful and I'd rather not pay for a "good used honest guv" tank in the hope the switch inside works..

A simple solution is a comparator circuit connected to the gauge, which will switch on the light at your chosen point. Any old op-amp would do the job and many of us could knock one up for you if you can't. I used one on an old Scimitar to switch the electric fan modification.

 

[bricol]

Just seen this - and the pictures. Keep a very careful eye on the fuel hoses if you've not already changed them. That bit of hose by the sender looks a bit ancient - which won't mix well with modern fuel. Hoses on a Scimitar SS1 I had simply rotted through (and drained the tank) despite otherwise looking fine.

 

[dave h 2]

Test from the other end. Take the tank connection off and ground it. Gauge should now show FSD. If it doesn't, ground the sender wire at the gauge and try again. That will diagnose the gauge and wiring as far as the tank.

As you've been told above by both AJ and Nomad a grounded gauge will read full, which is exactly what a single wire sender does. It is therefore pointless to measure the sender resistance in this case.
It's probably too late, but don't remove the sender till you absolutely have to, the gasket is thin rubber and tends to break up.
Check the wiring front to back, something may have rubbed through the insulation.

Earlier C3 vettes are like this, yours should be single wire.