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-   -   Gas Gauge not working...Sometimes (https://www.f150online.com/forums/1997-2003-f-150/515319-gas-gauge-not-working-sometimes.html)

chuck gibson 09-11-2017 09:18 PM

Gas Gauge not working...Sometimes
 
Hey Guys,
My gas gauge is occasionally not moving up at all. A couple of times I killed the truck and restarted it and it moved up just fine. Does anyone know of any wires or whatever to check out first?
Thanks!
Chuck

Bluegrass 09-12-2017 06:57 PM

First how the level gauge works so you can get some idea what's going on.
The fuel pump has a variable resistor that changes value with level changes.
The dash 'processor' converts the voltage changes to digital
then drives the fuel level gauge.
Its not a simple old time gauge circuit.
Could be a ground, harness leads, the plugup at the tank, level unit or a dash malfunction function.
.
First thing I would do is run the Dash Hec diagnostics and step to the fuel gauge reading that will show as an Octal number representing the tank level.
If you know the tank level it should relate to the Octal number. If not assume to issue is between the dash and the tank.
When stepping to FUEL the following will be seen for some level if there is no issue.
Octal 255 = open circuit.
232= full stop.
215= full tank +/- 10.
178= 3/4 mark +/- 8.
138= 1/2 mark +/- 7.
93 = 1/4 mark +/- 5.
41 = E mark +/- 4.
54= Low fuel light.
0 to 18= shorted circuit.
None of the numbers are Decimal or Binary unless converted for no useful reason..
.
This why I recommend you start here.
To access this test hold the reset button in then Ignition to run.
The gauges should all sweep as the first test.
There after pulse the reset button to step through to the Fuel Octal number on the mileage readout and compare to the info above.
Sorry its not simple but a digital system in use.
Any other way is just looking and guessing.
Good luck.

chuck gibson 09-12-2017 08:51 PM


Originally Posted by Bluegrass (Post 5223219)
First how the level gauge works so you can get some idea what's going on.
The fuel pump has a variable resistor that changes value with level changes.
The dash 'processor' converts the voltage changes to digital
then drives the fuel level gauge.
Its not a simple old time gauge circuit.
Could be a ground, harness leads, the plugup at the tank, level unit or a dash malfunction function.
.
First thing I would do is run the Dash Hec diagnostics and step to the fuel gauge reading that will show as an Octal number representing the tank level.
If you know the tank level it should relate to the Octal number. If not assume to issue is between the dash and the tank.
When stepping to FUEL the following will be seen for some level if there is no issue.
Octal 255 = open circuit.
232= full stop.
215= full tank +/- 10.
178= 3/4 mark +/- 8.
138= 1/2 mark +/- 7.
93 = 1/4 mark +/- 5.
41 = E mark +/- 4.
54= Low fuel light.
0 to 18= shorted circuit.
None of the numbers are Decimal or Binary unless converted for no useful reason..
.
This why I recommend you start here.
To access this test hold the reset button in then Ignition to run.
The gauges should all sweep as the first test.
There after pulse the reset button to step through to the Fuel Octal number on the mileage readout and compare to the info above.
Sorry its not simple but a digital system in use.
Any other way is just looking and guessing.
Good luck.

While pulsing the reset button, will the milage readout actually say "Fuel Octal"?

Bluegrass 09-12-2017 09:50 PM

No, only FUEL.
The number you see is an Octal number notation.
Sorry it confuses you.
A number is a number unless told to what base it was derived from. (Octal) in this case.
Good luck.

glc 09-12-2017 10:30 PM

What YEAR is your truck? The procedure only applies to 99-03.

Hold the reset button in and turn on the key. When it says test let it go. Then press the reset and repeat till it says FUELxxx where xxx is a number. I just did mine, I'm a bit under F on the gauge and my number was 206.

El_De_La_Lobos 09-12-2018 08:39 PM


Originally Posted by Bluegrass (Post 5223219)
First how the level gauge works so you can get some idea what's going on.
The fuel pump has a variable resistor that changes value with level changes.
The dash 'processor' converts the voltage changes to digital
then drives the fuel level gauge.
Its not a simple old time gauge circuit.
Could be a ground, harness leads, the plugup at the tank, level unit or a dash malfunction function.
.
First thing I would do is run the Dash Hec diagnostics and step to the fuel gauge reading that will show as an Octal number representing the tank level.
If you know the tank level it should relate to the Octal number. If not assume to issue is between the dash and the tank.
When stepping to FUEL the following will be seen for some level if there is no issue.
Octal 255 = open circuit.
232= full stop.
215= full tank +/- 10.
178= 3/4 mark +/- 8.
138= 1/2 mark +/- 7.
93 = 1/4 mark +/- 5.
41 = E mark +/- 4.
54= Low fuel light.
0 to 18= shorted circuit.
None of the numbers are Decimal or Binary unless converted for no useful reason..
.
This why I recommend you start here.
To access this test hold the reset button in then Ignition to run.
The gauges should all sweep as the first test.
There after pulse the reset button to step through to the Fuel Octal number on the mileage readout and compare to the info above.
Sorry its not simple but a digital system in use.
Any other way is just looking and guessing.
Good luck.

if its off what can i do?

Bluegrass 09-12-2018 09:25 PM

The fuel pump has a float on an arm.
This changes the resistance value and voltage sent to the Dash input as the level changes..
At the dash an analogue to digital converter (AD) makes the conversion to Binary then displays it as an Octal number readout..
The readout is converted back to analogue to be applied to the dash gauge in increments as the level changes on average.
The dash is all electronic from 2000 up and takes other digital signals in so it has to do the same for all the signals displayed as Octal, Binary and Decimal as the designer wanted it.
You have to make some tests of fuel pump gauge level readings to see if it's tracking with the right resistance vs fuel level.

El_De_La_Lobos 09-13-2018 12:27 AM


Originally Posted by Bluegrass (Post 5241258)
The fuel pump has a float on an arm.
This changes the resistance value and voltage sent to the Dash input as the level changes..
At the dash an analogue to digital converter (AD) makes the conversion to Binary then displays it as an Octal number readout..
The readout is converted back to analogue to be applied to the dash gauge in increments as the level changes on average.
The dash is all electronic from 2000 up and takes other digital signals in so it has to do the same for all the signals displayed as Octal, Binary and Decimal as the designer wanted it.
You have to make some tests of fuel pump gauge level readings to see if it's tracking with the right resistance vs fuel level.

what tests could i do. Also i had an issue with my tire ripping my wiring harness on the drive side replaced it had to do some repinning and had to sodder some stuff to make it work but yeah but each time i fill up all they way my gas gauge stops working and get an engine code i get a b1202 fuel sender circuit open(used a friends scanner)

Bluegrass 09-13-2018 02:12 AM

You already have the problem defined with the body code 1202.
How is the fuel gauge going to work with an open sender circuit?

As I explained, the float resistor signal circuit is open according the code 1202.
Find the open in the harness.
That's what volt meters and Ohm meters are for.
You have to do the volt meter testing with the ignition on so the dash is powered up and supplying the voltage to the float resistor.

El_De_La_Lobos 10-12-2018 12:52 AM


Originally Posted by Bluegrass (Post 5241271)
You already have the problem defined with the body code 1202.
How is the fuel gauge going to work with an open sender circuit?

As I explained, the float resistor signal circuit is open according the code 1202.
Find the open in the harness.
That's what volt meters and Ohm meters are for.
You have to do the volt meter testing with the ignition on so the dash is powered up and supplying the voltage to the float resistor.

Can i get a better explanation electrical is my weak point by far confuses me all the time and i was never really taught i try to look up videos and try to learn it but goes in through one ear comes out the other

Bluegrass 10-12-2018 01:28 AM

I'm sorry but I cannot help if you have no basic backgrounds in the Sciences.
This shows the best IPADS, IPHONES, TABLETS and Computers are of little value if the information found is not able to be understood.
Throw the dam things away and get into the books and learn something.
* What is an open circuit?
With applied voltage an open circuit cannot conduct electrons for the function intended.
Find the open in the fuel level circuit as the code tells you.
Good luck.


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