Fuel systems in cars don’t have the wow factor of performance upgrades such as turbos or aftermarket exhausts, but play a crucial role in storing and delivering fuel to the engine when needed. The aim is to provide the right amount of fuel for the engine load, ensuring efficient operation. Parts include fuel tanks, injectors, pumps, filters, fuel lines and hoses. Today’s systems are additionally aided by a multitude of sensors, ranging from oxygen seniors that help the ECU to distinguish between rich and lean fuel mixtures, and mass air flow sensors to balance fuel with air volume coming into the engine.
Fuel System Basics
Transferring fuel from the tank to the engine is done by fuel pumps. They do this by generating high pressure in the fuel line and with the help of the vacuum created in the cylinder and the crank at the bottom dead center position. Fuel is then pressurized, sent to the injectors and ready to be infected for combustion.
Pump Types
There are two main types of pumps – electric and mechanical.
Electric Fuel Pumps
These are the most common type in new vehicles, are located inside or near the fuel tank, and operate at high pressure. They’re highly efficient, require little to no maintenance, have a small footprint to save space, and are very quiet. To operate, they receive voltage from the car battery. In-tank types are the most common, but some vehicles have the pump positioned between the tank and engine, leading to easier replacements if something goes wrong.
Cars with direct injection combine features of mechanical and electrical pumps, with the parts located in the engine bay and driven by the crankshaft, cams, oil pump or vacuum pump. They generate much higher pressure (between 2000 and 3000 psi) to meet the specific needs of direct injection.
Mechanical
Older carbureted engines usually have a mechanical fuel pump, located inside the engine bay. To work, it relies on the motion of the crankshaft and belt. Advantages over newer electrical types are their simple design, generally lower maintenance needs, and longer lifespans. and that they don’t drain the battery. However, they can get noisy and are usually not as efficient.
How They Work
Electrical pumps power up when turning the ignition key, with voltage supplied from the battery. This activates an electric motor. The motor spins an impeller and creates a low-pressure zone inside the pump. This draws fuel through strainers to clear it of debris. Fuel that gets pushed past the impeller increases pressure within the fuel lines.
To ensure directional flow, check valves open and close to allow flow to the engine. Excess pressure is regulated by a pressure relief valve and diverts excess fuel back to the tank. Being submerged in fuel, the moving pump parts are also cooled and lubricated, ensuring the pump works as it should.
Signs of a Faulty Fuel Pump
Failing pumps lead to a significant drop in performance, starting issues and more:
- Hard starts – clogged or damaged fuel pumps are one of the reasons your car won’t start. The crank may be turning over, but with no fuel through the lines, there’s no combustion.
- Sputtering – Engines that sputter while accelerating due to fueling issues have damaged pumps to blame. The parts can’t produce the required pressure and air-fuel ratios for clean combustion.
- Surging – electrical issues in the pump can lead to abrupt surging, or spikes in the RPMs without working the gas pedal. This often happens at idle or lower engine speeds.
- Power loss – the engine losing puff in demanding driving conditions (inclines, overtaking, carrying heavy loads) is a sign of a bad pump that can’t generate the required pressure and fuel volume.
- Whining noises from the tank – loud, high-pitched whining or howling noises from the rear of the vehicle can mean insufficient fuel in the lines, contaminated fuel or advanced pump wear.
- Stalling and high engine temperatures – knocking, high pressure and heat from not enough fuel or lean mixtures can cause stalling, or in recurring cases serious engine damage beyond a bad fuel pump.
- Low gas mileage – poor fuel efficiency and more regular stops to fill up than usual point to worn fuel pump valves and rich fuel mixtures. Besides higher fuel use and elevated emissions, the issue can also lead to power loss, contaminated oil and engine failure.
Choosing Replacements
Standard replacement pumps are straightforward to buy. You’ll need a pump that meets your engine’s requirements in terms of fuel type, horsepower output, and whether it is carbureted (meaning a mechanical pump) or fuel-injected, most often an in-tank or in-line electrical type. Different types also exist for turbocharged and naturally aspirated engines.
Two key metrics are crucial when choosing a fuel pump for a modified or tuned engine – flow rate or the amount of fuel, and pressure, or the force at which the fuel is delivered and sprayed through the injectors to ensure smooth operation. Inadequate flow starves the engine of fuel, causing power loss, hesitation when on the gas and potential damage. Higher fuel rates result in rich mixtures with black exhaust out the tailgate, the giveaway sign. This can additionally cause contamination and lead to lower efficiency.
Getting the pressure right for a modded engine is a bit harder. Too little pressure disrupts efficiency, preventing proper atomization when fuel is sprayed. Adversely, too high fuel pressure leads to leaks and excessive strain and wear in the injectors. Both metrics are mutually dependent, so pumps that can deliver higher fuel volumes are also calibrated for higher pressure.
Also, if you’re running alternative fuel types like ethanol, flow rates will be different from standard octane gasoline. The last thing to consider is whether you’ll be using OEM or aftermarket replacements. OEM parts ensure a perfect fit, meaning simple installation and pumps that meet flow rate and pressure requirements. For a performance boost, and in engine overhauls, aftermarket pumps can provide higher pressure rates and more power. However, you’ll need new injectors, filters, and spark plugs among other mods.