Gas gauge not working? I think I fixed it.

[68gtxman]

Mr. Pawned, we salute your ingenuity and thank you for sharing!

 

[Pawned]

There are fuel quantity systems that use a variable power source to calibrate the gauge the same way you have done. Search Google for Texas Instruments LM317KCT data sheet. There is a lot of info on it showing how to make a simple and cheap variable power source. Most systems are impossible to calibrate on their full range, so most of them, especially on airplanes, are calibrated to read correctly at empty and not worry about the readings at full (the only time you can have too much fuel, is if you're on fire.)
Until someone makes a plug in system with a microcontroller and a stepper motor indicator, you may only get one point at which the gauge reads correctly.

Most correct. Unfortunately, my tank was not empty so I could not check it. But on the test bench, the gauge read empty when I had 6vdc on it and the variable resistor set at 9.6volts which is factory spec. But I do know for sure, that the gas gauge reached full just as the gas overflowed the tank
I do plan to run the car out of gas to see where it sets. Means I have to refill the gas can in the trunk.

Because of the low amperage regulator I put in, I just purchased 2 of these variable voltage regulator off of ebay. http://tinyurl.com/n84sy3h . For $1.15 how can you go wrong. So when the time comes to open it up again I will put them in.
I will modify them slightly. If you look at my gauges pix, you will see a small hole and recessed screw head below the gas gauge. That is a variable resistor that I was using for test. It is no longer hooked up, but when I use the board, I will remove the blue resistor and hook mine into the circuit. This way I should be able to adjust the voltage without pulling the cluster.

 

[Pawned]

Most correct. Unfortunately, my tank was not empty so I could not check it. But on the test bench, the gauge read empty when I had 6vdc on it and the variable resistor set at 9.6volts which is factory spec. But I do know for sure, that the gas gauge reached full just as the gas overflowed the tank
I do plan to run the car out of gas to see where it sets. Means I have to refill the gas can in the trunk.

Because of the low amperage regulator I put in, I just purchased 2 of these variable voltage regulator off of ebay. http://tinyurl.com/n84sy3h . For $1.15 how can you go wrong. So when the time comes to open it up again I will put them in.
I will modify them slightly. If you look at my gauges pix, you will see a small hole and recessed screw head below the gas gauge. That is a variable resistor that I was using for test. It is no longer hooked up, but when I use the board, I will remove the blue resistor and hook mine into the circuit. This way I should be able to adjust the voltage without pulling the cluster.

Correction in the first paragraph I said 9.6 volts, it should read 9.6 ohms

 

[Pawned]

I drove the car today, started out at about 3/4 tank. I drove maybe 40-45 miles and when I got home the gauge read almost empty. I got under the car and measured the resistance on the sending unit. It was right at about 26 ohms.

Back to the test bench. I used the spare fuel gauge I had. Again, I can not change the value of the resistance in the gauge or sending unit. The only thing I can change is the voltage. Near as I can tell, my gauge should have an input voltage 8.0 VDC

Very interesting as I had bought a 8 vdc regulator and then went back to the store to get the 6vdc regulator. I am not ready to pull the cluster again. So I plan to wait for the variable voltage regulators I ordered from China (for $1.15 each including shipping) to get here. Then I can adjust the voltage easier to dial it in.
If and when I do get it dialed in, at least so it reads empty when it is empty, I will take detailed pictures and draw up some schematics and post them.

How does that sound? :banghead::banghead:

 

[67Dart273]

I think I'm just gonna build in a reserve tank, LOL

You'd think I'd have time to do something like this. If I was younger and had more energy, I might. Just one more of them "irons in the fire."

 

[Pawned]

A reserve tank is not such a bad idea. It always worked on my motorcycles.
Even just get a sturdy 5 gallon Jerry Can and put a pit **** on it with a hose that fed down to the tank thru the grommet. I think I may do that also. Secure it in the trunk so it will not spill.

 

[67Dart273]

I'm not sure a Jerry can is the answer, LOL

"Back in" the first gas crunch in the 70's, I actually put an outboard tank in the trunk of my 70RR. It was securely strapped into eyebolts through the trunk floor, and vented out externally. Had an electric pump that would simply dump the contents into the main.

"Back then" the dammed service stations would leave their signs rotating and lights on, but they'd be closed and out of gas.

There was at least TWICE I finally pulled into a working station with both pumps rattling for something.

Seriously, here's a couple of things I thought...........

Small tank tucked up in the left quarter, with a "Y" in the flller would fill both. Electric pump on a toggle to transfer

Or, small tank up in the trunk. You could construct this so that the filler would go into the reserve, but the outlet into the main (filler) would come up inside the reserve........so the reserve would fill, then spill over into the main. That way you could fill both from one filler outside.

Again, a pump could either dump into the main, or electric selector valve, etc.

 

[Pawned]

The new adjustable voltage regulators from China arrived in today's mail.
I pulled the duster into the garage and will get started on it hopefully tomorrow.

I am very confident that this will be far more successful than the fixed regulator did. For $1.15 each shipping included, how can I go wrong?? (Don't answer that)

 

[67Dart273]

LOL. Read my signature

 

[Pawned]

LOL. Read my signature

I think I already said, I will fix it or die, whichever comes first :drinkers:

 

[RedFish]

I think I already said, I will fix it or die, whichever comes first :drinkers:

Where do we send flowers ? ROFL
I couldn't resist.

 

[CUDA69]

After battling my fuel gauge a bunch of times, I ended up putting in a speedometer with a trip odometer. Now I always fill the tank and reset the odometer to zero. 200 miles of normal driving and it usually takes about 13 gallons (18 gallon tank). A day at the road course requires filling it at lunch time (8 MPG, LOL).

 

[Pawned]

I have the new regulators, so I pulled the cluster. I have some better shots of what I built.
I will be taking those out and replace them with the new pcbs that just got here. Once I finish with the new parts and if it works, I will post clear pix and schematics

 

[67Dart273]

.................lurking....................monitoring...................

 

[ssba]

Still watching from the sidelines, fingers crossed.

 

[Pawned]

Still watching from the sidelines, fingers crossed.

I tried to remove the varible resistor from the board and extend it with wires.

I screwed it up. At my age, it is very seldom I can use my hands as well as I did only 5 years ago.
So I attached the entire board to the dash and used wires to the gauges.

I took a bunch of photos to post. I will wait until it works perfectly before I post them. Now I am taking a break before I put it back in the dash. More later
FYI, I ordered 5 more regulator boards at $1.15 each

 

[Pawned]

OK here is where I set on this project.
I have put the dash cluster with my modifications back in the car. I do not know how much gas is presently in the car so I can not dial it in.
I am able to move the needle from E to about 3/4. I will wait till I run it dry to know for sure if I succeeded.

Do you want me to wait to post my modification until I am absolutely positive it is a fix?
Do you want me to post the pictures and instructions before I am sure?
Should I open a new thread with my fix?

 

[skykeith]

You've already got it working. As I said in post 25, there are fuel quantity systems that work exactly the way you've done it. All you need to do is calibrate it to empty. I would like to see pictures of what you've done.

 

[Pawned]

Picture 1
shows the variable voltage regulator I ordered from China (cost $1.15 delivered ) .


Pix 2
Is the back of the dash board cluster. I actually removed a piece of plastic to the left of the hole to be able to align the regulators adjust screw with the hole in the dash


Pix 3
shows the placement of the hole I drilled in the dash


Pix 4, 5, 6
shows the wires attached and the board is tacked in place with hot glue


Pix 7
The adjustment screw is placed behind hole so I can adjust the regulator without removing the cluster.


Pix 8
Wires run thru the hole I cut in the metal can.


Pix 9
Orange wire is + output of adjustable regulator. Soldered to fuel gauge side of cut trace
Orange/wire wire is – output of regulator soldered to ground


pix 10 and 10b
blue wire is input to regulator. It can be soldered to any +12 vdc source. I chose to solder it to pin 1
on the pin connector.
Blue/white wire is – input. Attach to any ground




Pix 11
shows 5vdc regulator still feeding temperature gauge. I also placed a piece of plastic on the back of the regulator board so there is no chance of grounding out to the metal can


Pix 12
shows where I cut the trace between the two meter inputs so they can be fed by different sources.


I have not yet been able to calibrate the gauge as I do not know how much fuel is in the tank. I will wait until I run out of gas to calibrate the gauge exactly to the E. Then I will see how far the gauge
travels to the F.
I am mostly interested in when the gas is getting to Empty. I will just make a mental note where the Full is.

 

[Pawned]

The remainder of the pictures to the above mod.

One thing I did not pay attention to is the last pix. At the bottom left of the speedometer you will see a couple of the wires hanging in there.
As they are not in the way of the speedo needle, I did not bother to take it apart and fix that. Next time I pull the cluster I will fix that

 

[KitCarlson]

I can make a circuit with a 50 cent micro-controller and a few other components that will enable calibration of the empty and full. It works by separating the sender measurement, from driving the gauge. There will be a special calibration procedure performed at empty and full. It will correct for off specification senders and gauges, if they function in a monotonic manner.

If more than a few have interest, I will start a separate thread, develop the schematic, parts list and simple software for the system. I do not have interest in selling units, but I can see helping someone get setup up.

 

[red67gts]

I am interested in everyone's suggestions to help with this problem lots of us have. Thanks for sharing your knowledge because most of it is over my head

 

[zhandfull]

I'm following with interest as well. I have more than one A body gas gauge that doesn't work.

Pawned this is probably a stupid question but these cars have what I think is ground strap that goes from the sending unit to the fuel line. Not uncommon for them to be missing does your car have one? Mine are all broken or missing I was hoping that might be the problem with mine.

 

[67Dart273]

I can make a circuit with a 50 cent micro-controller and a few other components that will enable calibration of the empty and full. It works by separating the sender measurement, from driving the gauge. There will be a special calibration procedure performed at empty and full. It will correct for off specification senders and gauges, if they function in a monotonic manner.

If more than a few have interest, I will start a separate thread, develop the schematic, parts list and simple software for the system. I do not have interest in selling units, but I can see helping someone get setup up.

Dave, I for one would love to see this, and you could probably sell them. Engineering, 'specially on this new fangled stuff is where I fall down, LOL

 

[Pawned]

I'm following with interest as well. I have more than one A body gas gauge that doesn't work.

Pawned this is probably a stupid question but these cars have what I think is ground strap that goes from the sending unit to the fuel line. Not uncommon for them to be missing does your car have one? Mine are all broken or missing I was hoping that might be the problem with mine.

Yes I have one, but mine is in worse shape than the one in your picture.
So, long ago I added a 2nd grounding wire from the fuel outlet of the sending unit to chassis ground.