fuel sender question

-
S

swifter

Well-Known Member
Joined
Dec 18, 2008
Messages
2,391
Reaction score
75
Location
wis
Can someone explain the fuel sender circuit??? I know it acts on resistance does that mean the voltage from the gauge varies????? replaced a fuel cell and gauge does not work ,I know the mopar gauges are 10 to 70 ohm's but don't understand the voltage at my main post on the sender is only 4.5 volts?? should that be 12 volts or does that vary on how full the tank is??
also is the 10 ohm's empty or full?????
 
I may be stepping in early here; But voltage at the sender?
Dash uses 5.5 volts. You unhook the sender wire, and hook an ohmmeter pos to that, ground to tank. Fuel cell the same, but easier to pull the sender, same, but move the lever. Could be the ground to the dash/frame.
 
The gauges operate on 5 volts. The sender creates a resistance in the path of that 5 volts to ground.If the resistance is low the current flow is high , creates more heat in the gauge, needle goes higher.10 ohms is full.
At 73 ohms resistance in the path to ground very little current passes through the gauge, low heat generated, empty reading.
 
I wonder how many safety freaks would crap their pants if they knew that there was an uninsulated wire with electricity flowing through it inside their gas tanks! :cheers:
 
green1 and Redfish - Thanks for the info. I have an intermittant gas gauge after installing a new gas tank and sending unit and I'm basically ingorant when it comes to troubleshooting electrical stuff. Your info gives me enough limited knowledge to start with and may help me trouble shoot.

I'll get under there one day and see what I find and I may be back in here with some questions. Unfortunately - I have about a dozen things to work on and the gas gauge is somewhere further down the list than the fact that the gasket that came with the sending unit seems too thin because I have a slight gas leak.
 
'64 Cuda said:
I wonder how many safety freaks would crap their pants if they knew that there was an uninsulated wire with electricity flowing through it inside their gas tanks! :cheers:
Click to expand...

In theory it is impossible to blow up a fuel tank in this way. ANY amount of gasoline in the tank will evaporate to it's natural state of vapor pressure, and in a very short time, will create such a saturated over-rich mixture that it can not possibly burn.

There IS an "envelope" of combustible mixture. In the same way that a fuel cannot burn "too lean" it cannot burn "too rich," either.

My first real heavy electric fuel pump back in the '70's was a Carter motor drive. The motor in this pump operates submerged in fuel. Of course nowadays this is commonplace

fuelpump_cutaway.jpg
 
Ken71Twister said:
green1 and Redfish - Thanks for the info. I have an intermittant gas gauge after installing a new gas tank and sending unit and I'm basically ingorant when it comes to troubleshooting electrical stuff. Your info gives me enough limited knowledge to start with and may help me trouble shoot.

I'll get under there one day and see what I find and I may be back in here with some questions. Unfortunately - I have about a dozen things to work on and the gas gauge is somewhere further down the list than the fact that the gasket that came with the sending unit seems too thin because I have a slight gas leak.
Click to expand...

There is a ground strap that bridges the short piece of rubber hose between the sender and the fuel line. If it is not there the gauge will be weird if it works at all. It's just a short piece of flat metal that snaps on the lines and carries current around the hose.
 
Or get a 6" long piece of wire and using the small fuel line clamps put each end of the wire on the medal fuel line and tighten the clamps. This will bridge the short length of rubber hose at the sender.
 
The circuit board behind the dash could be bad. If you have a power source such as a jumper wire from the battery you can apply power directly to the lug on the gauge to ensure that it works. Make sure you ground the other lug. The lugs I'm referring to are the ones that bolts the gauge to instrument cluster. Do it only briefly though.
 
intermittent gauge is most often one of 2 faults. Either the ground strap mentioned before is loose or the gauge is loose from the printed circuit board.
 
You must log in or register to reply here.
-

Back
Top