What does the fuel gauge tell you?

What does the fuel gauge tell you?
Experienced mechanics share their insights in answering this question :
Without gas, your car won’t be going much of anywhere. The fuel gauge in the dash gives you information about how much gas is left in the tank, so you know when you need to find a gas station and fill up again.

The gauge runs from the full (F) mark to the empty (E) mark, with three additional marks in between (3/4, 1/2 and 1/4 tank). As you drive, the needle will fall from full toward empty. Before it reaches the E mark, you need to fill up the tank.

The symbol of a gas pump with an arrow on it (located under the E) reminds you that the gas tank is on the driver side of the car.

Tips

The fuel gauge only shows an approximation of how much gas is in the tank.
Driving on an uneven surface will cause the needle to vary from true. For example, while driving up or down an incline the needle may indicate a full tank of gas, while on a flat road it indicates only a half full tank. The level the needle points to when driving on a flat surface is true (assuming no existing faults and a half full tank of gas).

How to Identify and Fix Common car Problems ?

Our sources include academic articles, blog posts, and personal essays from experienced mechanics :

In automotive and aerospace engineering, a fuel gauge is an instrument used to indicate the amount of fuel in a fuel tank.
The gas gauge is very easy to read. All you need to do is look at the needle`s position on the gauge. The closer it is to F, the fuller your gas tank is. On the other hand, the closer the needle gets to E, the more empty your tank is.
The fuel gauge displays the information that is conveyed from the fuel sending unit, which is attached to/on/in the fuel tank. Based on that information, an analog gauge will move a needle up and down across a dial or a digital gauge will display a set number of bars that show how much fuel is left.
Fuel pressure for most vehicles should stay in a 5- to 10-psi range. But, techs should make sure to look at the service information for the specifications. Other data PIDs used to regulate the fuel pump include the engine position sensors.
The fuel gauge sender, also commonly referred to as the fuel sending unit, is the component responsible for sending the signal that operates the fuel level gauge in the instrument cluster. The fuel sending unit is made up of an arm, float, and a resistor that changes according the position of the float.
The gauge also has no way to accurately represent `top-ups` beyond the full tank a lot of people indulge in. The gauge doesn`t move for a bit after refuelling, but you`re still burning fuel just the same. The only way you`ll get a hang of what your car does is to observe and correlate over time.
The gauge is usually located on top of the tank, and is a clear glass or plastic tube marked with numbers that look like the gas gauge in your car: F, ¾, ½, ¼. A red marker or float indicates how much fuel is left in your tank.
No matter what operating condition (short of demanding more fuel than the pump can supply), pressure in the rail will always be 58psi (or pretty close). When idling at 20 inHg, this means effective pressure will rise to 68psi because the vacuum in the manifold is adding 10psi to the rails 58psi.
To reset the fuel gauge on a Ford, you will need to disconnect the battery and then reconnect it after about 30 seconds. This should reset the fuel gauge and clear any codes that may be causing it to malfunction. The fuel tank may need to be refilled after the reset.
A turbine fuel flow meter converts the mechanical action of the turbine rotating in the fluid around an axis into a flow rate. As the fluid impacts upon the turbine blades it sets the rotor in motion, and when a steady rotation speed is reached it is proportional the fluid`s velocity.
This issue is usually caused by one of a few issues – either the float has separated from the metal arm and isn`t sending any information about fuel level, the variable resistor is faulty and malfunctioning, or the wires in the system have corroded and are no longer sending information.
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.
The most common cause of an inaccurate or non-functioning gas gauge is a component called the sending unit. When you`re driving, the sending unit rubs against a variable resistor. This can lead to wear over the life of your vehicle.
One fault owners can almost certainly expect to develop on older machines and trucks is a fuel level gauge that eventually stops working. Repairing that problem isn`t too difficult, even if OEM replacement parts are no longer available. There are plenty of aftermarket components that can do the job.
Oil gauges look like most indicators on your dashboard. There`s a label (typically “OIL”), numbers (ranging between 1-80 or 1-100), and a dial with an indicator needle. Instead of numbers, some vehicles use “L” and “H” to indicate high or low pressure.
Beta. The 7/16 mark on a car fuel gauge typically indicates that the vehicle has approximately 43.75% of its fuel tank remaini. Continue reading.
Answer: The tank must lose 7/8 of its original volume in gallons which equals 7/8 (420,000) = 367,500 gallons.
Beta. The 7/16 mark on a car fuel gauge typically indicates that the vehicle has approximately 43.75% of its fuel tank remaini. Continue reading.
High fuel pressure will make an engine run rich, while low fuel pressure will make an engine run lean or not at all. Fuel pressure readings that are higher than manufacturers specifications are generally caused by a problem in the return line fuel components.
Beta. The 7/16 mark on a car fuel gauge typically indicates that the vehicle has approximately 43.75% of its fuel tank remaini. Continue reading.
Answer: The tank must lose 7/8 of its original volume in gallons which equals 7/8 (420,000) = 367,500 gallons.

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.

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.

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.

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.

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.

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.

Installed new delphi fuel pump and fram fuel filter. still no pressure on fuel rail valve and wont start. 2003 Chevrolet Tahoe
ANSWER : Hi there – I suspect you have weak power getting to the fuel pump. I would first check the voltage coming out of the fuel pump relay. If the contacts in the relay are burned, you will not get reliable current flow to the pump. Check the fuel pump ground as well (voltage drop across the ground, not just continuity). I recommend a fuel system inspection performed 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.

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.