Car and Truck Fuel System Operation

The fuel tank stores the fuel supply. The electric fuel pump, supplies fuel through an in-line fuel filter to the fuel injection system. The fuel pump provides fuel at a higher rate of flow than is needed by the fuel injection system. The fuel pressure regulator maintains the correct fuel pressure to the fuel injection system. A separate pipe returns unused fuel to the fuel tank.

 

The fuel tank stores the fuel supply. The fuel tank is located in the rear of the vehicle. The fuel tank is held in place by 2 metal straps that attach to the frame. The fuel tank is molded from high density polyethylene.

The fuel fill pipe has a built-in restrictor and a deflector in order to prevent refueling with leaded fuel.

The fuel fill pipe has a tethered quarter-turn type fuel filler cap. A torque-limiting device prevents the cap from being over tightened. To install the cap, turn the cap clockwise until you hear audible clicks. This indicates that the cap is correctly torqued and fully seated. A fuel filler cap that is not fully seated may cause a malfunction in the emission system.

The fuel level sensor consists of a float, a wire float arm, and a ceramic resistor card. The position of the float arm indicates the fuel level. The fuel level sensor contains a variable resistor which changes resistance in correspondence with the amount of fuel in the fuel tank. The powertrain control module (PCM) sends the fuel level information via the Class 2 circuit to the instrument panel (IP) cluster. This information is used for the IP fuel gauge and the low fuel warning indicator, if applicable. The PCM also monitors the fuel level input for various diagnostics.

The fuel pump is mounted in the fuel sender assembly reservoir. The fuel pump is an electric high pressure pump. Fuel is pumped to the fuel rail at a specified flow and pressure. Excess fuel from the fuel rail assembly returns to the fuel tank through the fuel return pipe. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The powertrain control module (PCM) controls the electric fuel pump operation through a fuel pump relay. The fuel pump flex pipe acts to dampen the fuel pulses and noise generated by the fuel pump.

The fuel strainer attaches to the lower end of the fuel sender. The fuel strainer is made of woven plastic. The functions of the fuel strainer are to filter contaminants and to wick fuel. The fuel strainer is self-cleaning and normally requires no maintenance. Fuel stoppage at this point indicates that the fuel tank contains an abnormal amount of sediment or water.

The fuel filter is located on the fuel feed pipe, between the fuel pump and the fuel injectors. The paper filter element traps particles in the fuel that may damage the fuel injection system. The filter housing is made to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There is no service interval for fuel filter replacement. Replace a restricted fuel filter.

Nylon pipes are constructed to withstand maximum fuel system pressure, exposure to fuel additives, and changes in temperature. There are 3 sizes of nylon pipes used in most GM cars and trucks: 9.53 mm (3/8 in) ID for the fuel feed, 7.94 mm (5/16 in) ID for the fuel return, and 12.7 mm (1/2 in) ID for the vent. Heat resistant rubber hose or corrugated plastic conduit protect the sections of the pipes that are exposed to chafing, high temperature, or vibration.

Nylon fuel pipes are somewhat flexible and can be formed around gradual turns under the vehicle. However, if nylon fuel pipes are forced into sharp bends, the pipes kink and restrict the fuel flow. Also, once exposed to fuel, nylon pipes may become stiffer and are more likely to kink if bent too far. Take special care when working on a vehicle with nylon fuel pipes.

The fuel injector assembly is a solenoid operated device, controlled by the PCM, that meters pressurized fuel to a single engine cylinder. The PCM energizes the high-impedance (12 ohms) injector solenoid to open a normally closed ball valve. This allows fuel to flow into the top of the injector, past the ball valve, and through a director plate at the injector outlet. The director plate has four machined holes that control the fuel flow, generating a spray of finely atomized fuel at the injector tip. Fuel from the injector tip is directed at the intake valve, causing the fuel to become further atomized and vaporized before entering the combustion chamber. An injector stuck partly open can cause a loss of pressure after engine shutdown. Consequently, long cranking times would be noticed on some engines.

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  • Guest - larry

    No power to fuel pump and injector.

  • Guest - Emma

    Will a hole in the pipe you add transaxle fluid to for your transmission cause backing up/leaking or other issues? Hole is about 3 inches down, looks like the arm the pipe was resting on broke off, leaving a small hole. Was told it wasn't a big issue? Thanks<br />Not sure if this is the right spot to ask.

  • Guest - Stan4

    That is the intake air temperature sensor. It is either a small 2-wire sensor in the intake air duct, or it is internal to the Mass Airflow Sensor (MAF).

  • Guest - Lawrence Hotvedt

    I wish to install a power chip in my 2006 Dakota 4.7 V8 to try to get better mileage. The directions say to attach it to the IAT sensor. I am not sure which sensor that is. Are you able to help me? Thank you L

  • Guest - John

    1994 Chevy S-10 p/u starts with a shot of starting fluid, runs for twenty minutes good, then shuts off. Does not start back up until you spray starting fluid.

  • Guest - Slomotaom

    In reply to: Guest - John

    Sounds like either a bad fuel pump, injector, or you have a bad vacuum leak. This would cause a lean condition and stalling. A shot of starter fluid gets it rich enough to start.

  • Guest - Bob

    1992 S10 4.3L vortec engine running rough.I noticed fuel dumping out of driverside exhaust manifold. Replaced spider injector with hoses and the feed and return lines coming from fuel tank. Fuel still dumping out of driverside exhaust manifold.I pulled upper plenium, keyed system, and checked for gas leaks. Had none. My only way to work. Don't know what to do. Can't afford a garage to do repairs. NEED HELP!

  • Guest - Tech

    In reply to: Guest - Bob

    Only way to get fuel like that is a leak, sticking open injector, constantly injector being fired, or leaking fuel pressure regulator.

  • Guest - kieth

    Fuel problem.

  • Guest - bruce

    2002 Aztec pulled it in to change the r&r light front brakes and head light bulbs, now it won,t start. The fuel pump is not working, also.