Hello everyone!
I want to know if it is possible to calculate the fuel level in my Pontiac Firebird 3.4 V6 1995 by connecting an Arduino on the existing circuit without risking to create a default custom gauge dashboard or worse, a short Circuit ...
There are examples on the net to replace a faulty gauge, but I found nothing on a secondary branch ...
(I do not want to add a second probe in the gas tank)
In advance thank you for your help !!!
Sincerely,
Nitrix
Do you mean that you want to use the Arduino as well as, or in place of the existing fuel gauge. The latter would be easier.
Perhaps you can measure the voltage at the input to the fuel gauge with a multimeter and see how it varies with the fuel level ? If that gives a useful reading then you could use the Arduino to measure the voltage and display it as a fuel level.
...R
Please ensure that any replies to your identical thread in the French section are translated and posted here.
AWOL:
Please ensure that any replies to your identical thread in the French section are translated and posted here.
No problem! I expect to have a solution and will do his translation 
Thank you for your reply Robin,
Yes, I have to measure the fuel level on the existing circuit
My project is to make a LCD meter, the alpha version is HERE
In France, we can not replace the original counter, so I have to fix my LCD above the original counter. All other datas are provided to me by the computer of my Firebird, except the fuel level...
I thought to use a voltage divider, what is confirmed by me on the French part of the forum), but there is talk of a tank filled with gasoline, and I really do not want my car turns into rocket
I will post the plan of my full assembly shortly to actually see if what I think is valid.
Robin2:
Do you mean that you want to use the Arduino as well as, or in place of the existing fuel gauge. The latter would be easier.Perhaps you can measure the voltage at the input to the fuel gauge with a multimeter and see how it varies with the fuel level ? If that gives a useful reading then you could use the Arduino to measure the voltage and display it as a fuel level.
...R
Here is my wiring diagram, remains to be seen if it is correct, it would surprise me 
CABLAGE ESSENCE ARDUINO V2.pdf (112 KB)
The 50 Ω resistor connected to the sensor will change the reading on your existing gauge. You have also forgotten the effect of the current flowing through the existing gauge will have on your calculations.
Have you tried Robin's suggestion in reply #1?
Russell.
This is what I feared ...
I have carefully read the answer of Robin. But I rarely drive at this time, the calibration may take some time ...
do you have can bus or obd available on the car?
AFAIK, a fuel sensor just draws current from/through the fuel gauge in the dash.
The gauge and the sensor form a voltage divider, so on the sensor you will find a varying voltage that can be read by the Arduino.
If you use relative high resistor values (>10k), you won't influence the existing sensor.
Don't use a second (50ohm) load. That will upset the original fuel gauge.
What you do have to know before you start designing a circuit is the voltage on the sensor when the tank is full and when the tank is empty, without anything else connected to it.
You might need these voltages with engine running, and engine off.
Leo..
Nitrix:
But I rarely drive at this time, the calibration may take some time ...
Calibration will be essential - both to understand how the system works and to determine the correct values for your final program.
...R
adamants:
do you have can bus or obd available on the car?
It's an old similar technology, a specific General Electric protocol, named ALDL
I can read a big list of parameters whith a specific application (SCAN9495) : speed, rpm, coolant temperature, but not the fuel level 
Robin & Wawa,
I will perform the measurement with a voltmeter to know precisely the voltages before going further!
Thanks a lot for your help !!!
GM fuel sensors in that era are typically 90 to 0 ohms. Voltage should read between approx. 1 to 12v.
As was mentioned with high value resistors it won't affect the original gauge much.
