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Ive been searching for a while about my issue in here and haven’t come to a solution.
I have a new sending unit. I installed it correctly and my tank reads empty. Before I installed it, it read full and not stuck on empty. What can i do to fix this? Is there a bad ground? It’s grounded on the underside of the truck. Please help.
It means that there is a place somewhere along the wire between the dash gauge and the sending unit at the rear of the car where there is an unintended connection to the vehicle chassis. The wire could be pinched somewhere. Or something else. Trace the wire from the sending unit to the gauge and look for a place where the wire is bare where it's not supposed to be and touching metal.
While you're at it, read up on the concept of a short circuit. You have to know what the term means if you're ever going to do any kind of electrical troubleshooting.
Check the connections of the wire at the tank around where you replaced the sender. Its something you did as the symptoms of the original problem were an open circuit probably inside the sender unit.
Check the connections of the wire at the tank around where you replaced the sender. Its something you did as the symptoms of the original problem were an open circuit probably inside the sender unit.
So I remove the ground and just plug into hot wire, the fuel gauge should be stuck on Full, right?
A little back story I guess.....the fuel sender was never plugged in. The fuel gauge showed Full with no fuel sender plugged in. Soon as I plugged the sucker in and turned to on position, the hand went all th way to E.
A little back story I guess.....the fuel sender was never plugged in. The fuel gauge showed Full with no fuel sender plugged in.
This is normal behavior. The fuel gauge system is just a variable resistor with the resistance determined by the position of the float in the tank. The fuel gauge on the dash is just an Ohmmeter that measures that resistance. Resistance varied in these units from 0 to 90 Ohms, with 0 = E and 90 = F. If the sending unit is disconnected, the dash gauge is seeing an open circuit, which is infinite resistance. In such cases, the gauge usually points not just at F, but well past it, and this is what many people see if their gauge circuit is open for some reason (bad ground, disconnected or broken wiring, or a defective sending unit).
So the gauge SHOULD show full with no sender plugged in. If it shows E when the sender is connected, either the tank is empty or there is a short circuit, as we've noted above.
The tan wire is the negative side of the gauge looking for variable resistance to ground, as Jaunty explained. If you unplug the wire it will go past full with the key on. If touch that same wire to ground (any metal on the car) it will go to E. If it does both of those, your issue is 99% most likely the sending unit in the tank.
Thanks for all the help. So I just took off the ground to the trunk to see he gauge reads full. Nothing happened. It’s stuck at empty.
If you've disconnected the wire from the sending unit at the tank and the gauge reads "E" w/ the ignition ON, this is a symptom of a short FROM the wire between the gauge and sending unit TO chassis ground somewhere along the way. If there was no short, then the gauge should read past "F" w/ the sending unit disconnected.
Connecting the sending unit with an empty tank and getting a gauge reading of "E" is normal, however it COULD also indicate a short in the wiring to ground (the only way to know for sure is to disconnect the sending unit and the gauge moves to past "F").
So I just took off the ground to the trunk to see he gauge reads full. Nothing happened. It’s stuck at empty.
Johnny just made an important point that I was going to make that I don't think has been mentioned. You need to be doing all tests with the ignition key in the ON position. What the gauge reads with the key off means nothing as no power is getting to the system. (If you've already been doing this, please disregard this message.)
Thanks for the advice. I understand now. I think I have to isolate the issue, but let me ask this question. Shouldn’t that telltale cluster be grounded somewhere in the front? The reason I ask is because I’ve taken the dash out and prepping it to restore it. I thought this was a good time to make sure my gauges are working.
There must a ground wire issue in the dash, right?
There must a ground wire issue in the dash, right?
No. The gauge circuit is not grounded at the dash. One side of the gauge is connected to 12V from the battery, and the other side is connected to the long wire that runs from the gauge to the sending unit. The circuit is completed by the second wire coming from the sending unit, the ground wire, which needs to firmly attached to non-corroded metal at the rear of the car. The negative side of the battery is also grounded, and that's how the circuit completes. If you've got some kind of ground at your dash gauge, that could be the short circuit we've bee talking about and account for the gauge reading E all the time. There is no ground at the dash, at least for the fuel gauge circuit.
No, the fuel gauge has 2 connections for it to work (outside of the lamps), one side is 12v the other is the variable ground feed from the tank sending unit.
Here's a schematic of the fuel gauge circuit. It's about as simple an electrical circuit as you'll find. If your gauge is reading E all the time, you have a short to ground somewhere between the gauge and the sending unit. That "connector" is usually around the rear license plate area. You've certainly found it if you've replaced the sending unit.
Disconnect that connector and turn the key on. They gauge should go to F. If it does not, there is a short in that wire or the gauge or even the power supply to the gauge. If it does go to F, then ground the wire from the gauge. It should go to E. These are the two simple, basic, time-honored tests that determine if the gauge and the wiring between the gauge and the rear of the car are OK. If you do not get these results, there is a problem no matter how pretty the tan wire is. We've pretty much told you everything there is to say about troubleshooting fuel gauge systems. The rest is up to you.
Disconnect that connector and turn the key on. They gauge should go to F. If it does not, there is a short in that wire or the gauge or even the power supply to the gauge. If it does go to F, then ground the wire from the gauge. It should go to E. These are the two simple, basic, time-honored tests that determine if the gauge and the wiring between the gauge and the rear of the car are OK. If you do not get these results, there is a problem no matter how pretty the tan wire is. We've pretty much told you everything there is to say about troubleshooting fuel gauge systems. The rest is up to you.
I know it’s something else. I appreciate the help a lot. I’ll look at the more wires sooner or later.
Disconnect that connector and turn the key on. They gauge should go to F. If it does not, there is a short in that wire or the gauge or even the power supply to the gauge. If it does go to F, then ground the wire from the gauge. It should go to E. These are the two simple, basic, time-honored tests that determine if the gauge and the wiring between the gauge and the rear of the car are OK. If you do not get these results, there is a problem no matter how pretty the tan wire is. We've pretty much told you everything there is to say about troubleshooting fuel gauge systems. The rest is up to you.
quick question. Was all of the above methods the ONLY way to test the gauge?
Dammit I figured it out. There is a ground wire in the dash. This is what I was getting at before. I touched the wire to the metal dash frame and the needle move to full. Thanks for the help. Will continue to move forward.
April 19th, 2018, 12:57 PM
