Fuel gauge acting erratically

My fuel gauge is acting erratic. It stays on full for a while, then the low fuel level light comes on when it is at full. I think it could be a problem with the fuel tank sending unit.
Experienced mechanics share their insights in answering this question :
It’s possible that you have a problem with your fuel gauge. The only way to tell is to pull the fuel pump out and check resistance on the sending unit. I would suggest having a certified technician come out and remove the fuel tank and check resistance on the sending unit and, if needed, replace the fuel pump and sending unit.

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The problem could be caused by a faulty sending unit located in the tank, corroded or loose contacts on the wiring plugs, or a bad actuator at the fuel gauge on your dash. Start by locating the sending unit on your fuel tank.
A fuel gauge that reads full or empty all the time, or has a needle that moves erratically, could be the result of a faulty sender unit or fuel gauge itself.
Press and hold the “Trip/Odo” button and turn the car back on. While you`re holding the button, turn the key back to the “ON” position. Hold the button down for another 2 seconds after the car`s back on, then release.
A fuel level sensor (FLS) is used in all automobiles to indicate fuel level. Various methods are used to measure fuel level such as resistive film, discrete resistors, capacitive, and ultrasonic. Resistive-based sensors are most commonly used for this application.
Remove the ground connection, clean, and re-attach. You need to visually inspect the wiring as any break or damage to the sending unit wire, or ground will cause a problem at the gauge. In most cases, to gain access to the fuel tank sending unit mount / fuel pump mounting hole, you`ll need to drop the gas tank down.
The switch will usually come with a reset button that will reactivate the fuel pump if the switch was tripped. The fuel pump switch is an electrical component, and just the same as the rest on the vehicle, over time it can wear out and develop issues.
Common signs include the Check Engine Light coming on, the car not feeling right when running, and issues with starting the car.
The fuel gauge sender is located in the fuel tank and attached to the fuel pump. The sender has a base with a rod and float attached to it.
If the fuel rail sensor is bad, then the correct fuel pressure may not be achieved, resulting in the absence of sufficient fuel required for starting up. You may find that the engine cranks and maybe even fire up a couple of times before immediately dying.
The most common cause behind a faulty fuel gauge is sending unit failure. When your car is moving, the sending unit is in constant motion, rubbing the variable resistor constantly. As a result, over time, the contacts can wear off. This leads to an open circuit.
An inaccurate fuel tank reading is most commonly caused by the sending system which reads the fuel tank level and sends the reading to the gauge. Issues can also stem from a bad gauge, blown fuses, or corroded wiring. You can self-test all of these parts at home with a few tools.
Without a properly charged battery, the fuel injectors may not add fuel to the cylinders as efficiently as they normally would. This has the potential to cause more loss of fuel mileage than the alternator simply running all of the time.
Some sensors change how the engine behaves when it receives information from the control module. The idle air sensor, coolant temperature sensor and EGR sensor all change things within the engine and fuel delivery system.
Poor fuel economy: a faulty oxygen sensor will upset the air to fuel mixture resulting in increased fuel usage. Rough engine idle or misfiring: since the oxygen sensor output help control engine timing, combustion intervals, and air to fuel ration, a faulty sensor can cause the vehicle to run rough.
Fuel moves inside the tank while you are driving, which causes the sensor which is just a float attached to a potentiometer (variable resistor) and the sloshing causes the signal to fluctuate.
A partially plugged up radiator. A bad temperature gauge. A bad temperature sending unit. Dirty wiring connections between the sending unit and gauge.
If the fuel gauge reads full at all times, the probable causes are: The wire between the sender and gauge is broken and/or the connections are not good. The resistance wire in the sender is broken. The sender is not grounded and/or the tank is not grounded to the chassis.
A partially plugged up radiator. A bad temperature gauge. A bad temperature sending unit. Dirty wiring connections between the sending unit and gauge.
Running the vehicle on low fuel often can damage the fuel pump over time, which affects the fuel pressure. Fuel cools the fuel pump, and less fuel means there`s a greater chance fuel pump components can overheat or wear out. Low fuel can also draw air into the pump, preventing a consistent flow of fuel.
Running the vehicle on low fuel often can damage the fuel pump over time, which affects the fuel pressure. Fuel cools the fuel pump, and less fuel means there`s a greater chance fuel pump components can overheat or wear out. Low fuel can also draw air into the pump, preventing a consistent flow of fuel.
If the fuel gauge reads full at all times, the probable causes are: The wire between the sender and gauge is broken and/or the connections are not good. The resistance wire in the sender is broken. The sender is not grounded and/or the tank is not grounded to the chassis.
Running the vehicle on low fuel often can damage the fuel pump over time, which affects the fuel pressure. Fuel cools the fuel pump, and less fuel means there`s a greater chance fuel pump components can overheat or wear out. Low fuel can also draw air into the pump, preventing a consistent flow of fuel.

Relevant Questions and Answers :

the most relevant questions and answers related to your specific issue

I have a 1981 e-350 with dual fuel tanks the p.o. added a third tank and 3 electric fuel pumps along with sepparate gauges and swi
ANSWER : The switch you are referring to is vended with the required electrical and fuel schematic (I just looked in the box) that answers your installation question. If you want an advance view, here is a link as well. Yes, you need a return line and just refer to the aforementioned link. If you are retrofitting back to OEM, I strongly encourage you to buy the original Factory Service Manual (FSM). There are lots of details attending this system and obviously it is difficult to recount it all here. The FSM will make your life much easier and you can then make sure your installation is perfect. Alternatively, YourMechanic can dispatch a certified mechanic and perform the whole retrofit and check out if you desire. Just request and schedule a generic service such as fuel pump service and the mechanic will come to your location and estimate the parts and labor required. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.

Read Full Q/A … : Fuel gauge acting erratically

the car is acting like its getting to much fuel. changed the fuel pump, fuel filter, and the fuel pump relay.
ANSWER : There could be a few things contributing to your problem. You are correct that clogged or sticking fuel injectors and possibly the fuel pressure regulator could be faulty. A plugged catalytic converter can also cause the vehicle to bog down. A failing throttle position sensor can cause the symptoms you describe as well. I suggest having a certified technician, like one from YourMechanic.com, do a few tests to determine the exact cause of your starting concern.

Read Full Q/A … : Fuel gauge acting erratically

Fuel gauge acting erratically
ANSWER : It’s possible that you have a problem with your fuel gauge. The only way to tell is to pull the fuel pump out and check resistance on the sending unit. I would suggest having a certified technician come out and remove the fuel tank and check resistance on the sending unit and, if needed, replace the fuel pump and sending unit.

Read Full Q/A … : Fuel gauge acting erratically

Replaced fuel pump. Car won’t start. 2002 Infinity I35
ANSWER : Hi there – the metal component you describe is a fuel check valve on the fuel return line. Its function is to maintain a small amount of pressure in the fuel system so that starting does not require the fuel pump to run very long before the engine will start. Having replaced the fuel pump and fuel filter, I would check fuel pressure while the car is running. This is to check the fuel pump relay for burned contacts that won’t support full electrical current to the pump, and for proper fuel pressure – a malfunctioning fuel pressure regulator could also restrict power and higher speeds if pressure is too low. I would recommend an inspection of the fuel system by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.

Read Full Q/A … : Fuel gauge acting erratically

Fuel pressure
ANSWER : Hello,
You may want to try checking the fuel pump relay. The relay wires should have ground on two wires, power on one wire and switched power on another wire. To activate the fuel pump your ECU actually connects one of the ground wires to complete the circuit and send power to the fuel pump. If the wires all have power running through them, then it is likely you have a faulty relay. The wire coming from the fuel pump is the other ground wire. I would recommend having an expert from YourMechanic come to your location to diagnose your wiring as this can be very difficult and time consuming without the proper wiring diagram.

Read Full Q/A … : Fuel gauge acting erratically

Just replaced my fuel pump but its not getting any power tested fuel pump relay and fuel fuse both good tested the wires all good.
ANSWER : You need to look at the theft light on dash to make sure it comes on and goes off when you turn the key to the on position. If light comes on and stays on then your theft system is causing the fuel pump to not be engaged. I recommend you check the theft system and then scan the computer for theft system codes. You may need to reprogram the keys to work or you have an bad sensor for the ignition key in the steering column.

Read Full Q/A … : Fuel gauge acting erratically

How long and what is the process to replace a fuel pressure sensor?
ANSWER : A professional mechanic would require roughly 5 hours. (If just the regulator is replaced that takes about 1 hour). Some parts, as noted below, cannot be re-used, you need a precision inch pound torque wrench, FSM instructions (and TSB updates if applicable; procedure was changed in 2007 for instance) and the system has to be bled when done.

Below is partial list of steps, copied and pasted directly from the service manual:

1. Disconnect battery and put protective material in front of the charge air cooler (CAC) or damage to the CAC may occur.

2. Remove air cleaner assembly.

3. Disconnect the oil drain tube from the crankcase vent oil separator.

4. Loosen the air cleaner outlet tube clamp and detach the air cleaner outlet tube from the turbocharger.

5. Remove the bolts, the crankcase vent oil separator and the air cleaner outlet pipe as an assembly.

6. Remove and discard the crankcase vent oil separator press-in-place gasket. (To re-install, tighten to 13 Nm (115 lb-in).

7. Disconnect the PCM electrical connector (BE SURE BATTERY IS DISCONNECTED FIRST!) and retainer. Disconnect the in-line electrical connector and position the engine wiring harness on the engine.

8. Remove the pushnuts and the glow plug module heat shield.

9. Disconnect the high-pressure fuel injection pump electrical connector and detach the retainer from the glow plug module bracket. Disconnect the glow plug module and the exhaust gas recirculation temperature (EGRT) sensor electrical connectors, detach the wiring retainer and position the wiring harnesses aside.

10. Remove the nut and position the ground strap aside. To install, tighten to 13 Nm (115 lb-in).

11. Remove the engine wiring harness bolt. To install, tighten to 13 Nm (115 lb-in).

12. Remove the heater supply tube nut. To install, tighten to 13 Nm (115 lb-in).

13. Remove the bolts and the glow plug module bracket. To install, tighten to 13 Nm (115 lb-in).

14. Remove the nut and position the transmission fluid indicator tube aside. To install, tighten to 8 Nm (71 lb-in).

Warning: Do NOT disconnect the glow plug electrical connector before dislodging the seal from the valve cover or the wiring harness may be damaged.

15. Using an appropriate tool, dislodge the glow plug wiring harness seals from the valve cover.

16. Disconnect the glow plug electrical connectors by pulling on the glow plug wiring harness tee above the seal. Remove the glow plug wiring harness.

17. Remove the nut and position the crankcase ventilation drain tube aside.

18. Disconnect the wiring harness retainer from the valve cover stud.

19. Disconnect the wiring harness retainer from the generator bracket.

20. Disconnect the A/C pressure switch electrical connector. Position the harness aside.

Warning: Do not bend or flex the heater supply tube or damage to the tube may occur.

21. Remove the stud bolts, bolts and the valve cover. Remove and discard the valve cover gasket. To install, tighten to 9 Nm (80 lb-in).

Warning: Contact with exposed fuel injector wiring, if energized, may result in electric shock.

Use care when working on or around energized fuel injector wiring. Fuel injector wiring supplies HIGH VOLTAGE to operate the fuel injectors of course, you disconnected the battery though.

22. Disconnect the fuel rail pressure (FRP) sensor electrical connector.

Warning: Fuel injection equipment is manufactured to VERY precise tolerances and fine clearances (think space shuttle). To prevent fuel system damage, it is essential that absolute cleanliness is observed when working with these components. Always install fuel system caps on any open orifices or tubes.

23. Remove the FRP sensor. To install, tighten the FRP sensor in 2 stages.

Stage 1: Tighten to 7 Nm (62 lb-in).
Stage 2: Tighten an additional 40 degrees.

24. Bleed the high-pressure fuel system.

If you feel like this job may be too overwhelming or run into any issues, consider YourMechanic to get it done. One of our mobile technicians can come to your home and replace the fuel pressure sensor at your own convenience.

Read Full Q/A … : Fuel gauge acting erratically

I have a truck that won’t run and is not getting gas to the engine. Fuel pump is running, have a new filter and new fuel pressure
ANSWER : Hi There,
It sounds like you may have a clogged fuel injector or potentially a faulty injector that is fried internally. I would suggest testing them if you have access to a multi meter. Disconnect the injector from the electrical connector and set your multi meter to Ohms mode and measure the resistance of the injector. After testing all injectors, compare the resistance. They should be the same or very close. If they are not, they will likely need to be replaced.

Read Full Q/A … : Fuel gauge acting erratically

Eric smoalih

I am a certified master technician with the National Institute for Automotive Service Excellence (ASE), and I have been working as an auto mechanic for over 15 years. I am passionate about my work, and I take great pride in helping people keep their cars running smoothly.