Common Problems With Low Pressure Mechanical Fuel Pumps
Older model cars with carburettor engines use low pressure mechanical fuel pumps to pump fuel from the fuel tank to the engine. They are mounted outside of the tank, mainly on the side of the engine. With the advent of fuel injection systems, most mechanical fuel pumps are being replaced by electric ones, although few older car owners still have these pumps.
Low pressure mechanical fuel pumps are less functional compared to electric versions and incur frequent problems that lead to drivability problems. However, in newer car models with GDI-equipped engines, they are making a comeback. There is an electric fuel pump in the tank that supplies fuel to a mechanical fuel pump mounted on a high pressure engine.
In this article, we will look at just the common problems with low pressure mechanical fuel pumps used in carburettor engines along with ways to identify and resolve them.
Steam lock: Vapor lock occurs when liquid fuel in the supply system changes to a gaseous form and blocks the passage of fuel. As it is located in the engine compartment, the high heat from the engine on the pressurized side of the pump boils the fuel in the fuel lines, leading to vaporization.
Due to the vapor lock, the operation of the fuel pump is disturbed. It causes a loss of supply pressure, resulting in a loss of power transmission to the engine or a complete lock-up of the vehicle. Common signs of vapor lock are low or no fuel pressure, dry carburetor air horn and no throttle pump discharge, stalling, difficult starting, and low power.
Fuel foam: It occurs when cold fuel enters a hot carburetor, causing a series of short jerks in acceleration and ultimately resulting in a dead engine. Common signs are black smoke emitted from the tailpipe, wet carburetor air horn, and engine starting after a fully open throttle handle.
Alcohol blends: Gasoline additives, such as alcohol blends and octane boosters, affect gasoline volatility and cause performance and drivability problems. These additives also cause corrosion in the fuel system, dislodging rust and foreign particles in the tank, leading to filter clogging and ultimately affecting the functionality of a fuel pump.
Causes of failure: A worn or leaking diaphragm inside a mechanical fuel pump leads to its failure. A leaking diaphragm results in a fuel leak or a loss of fuel pressure. This eventually increases the pressure on the pump causing it to fail. Even leaky inlet or outlet valves and broken spring also result in the same.
Before the fuel pump stops working completely, it shows some signs of failure. Identify these signs and fix the problem as soon as possible. Although there are professional troubleshooting techniques to check functionality, there are some other simple ways that help you identify the bad one, even if you are a hobbyist.
• In the initial stages of a faulty fuel pump, you may experience lack of power, starting problems, sputtering, and so on.
• Fuel leaking from the pump indicates a bad diaphragm, so replace it.
• Inspect the throat of the carburetor by removing the air filter, then pump the throttle link and check for any fuel squirting into the carburetor. No jet of fuel can indicate its failure.
• Disconnect the fuel line at the carburetor and place it in a container. Start the engine and see if the fuel pump is pumping fuel. Constant jets of fuel indicate that it is working properly, while a weak flow or no fuel indicates that it is failing.
• Remove the dipstick to check the oil level. Oil level above the full mark can indicate a diaphragm leak as it allows fuel to seep into the crankcase, diluting the oil and increasing oil levels.
Timely repair / replacement prevents engine problems: Engine performance is adversely affected if issues are not addressed in a timely manner. If it cannot supply the fuel with the required pressure, it shuts down the engine and eventually stops running. Therefore, timely identification and resolution of the problem is essential to avoid engine problems.
Make sure you are using reliable after-market products while replacing engine components. It is important for the best performance of the fuel supply system.