Inspecting Mechanical Fuel Pump


Aug 29, 2012
Mechanical fuel pumps were generally used in older engines that are without fuel injection. Their simple construction makes them inexpensive and reliable, but they can be overlooked as bad, if the fuel pipe that brings the fuel from the tank to the pump is not intact. An automobile engine that runs lean, stalls or hesitates, misfires could have a leaking valve or diaphragm within the fuel pump. These complications cause the fuel pressure to drop and starve the fuel’s carburetor. Removing and replacing the pump
Before assessing the fuel system, always make sure that the supply hose is not exposed or leaking as the fuel is flammable. Try to avoid breathing its vapors or touching it with bare fingers. • If the mechanical pump needs to be replaced, disconnect the fuel lines from the pump. Then, Plug the inlet line so that fuel does not leak out. • Detach the fuel pump bolts from the engine and once the bolts are removed, the pump should come off. • Now, remove the gasket from the mounting surface of the engine and clean it thoroughly. Make sure that the gasket residue does not get into the engine. • Install a new gasket on the pump. Apply gasket sealer all around the gasket for a leak free seal. Also, apply a dab of grease at the pump lever tip where it contacts the camshaft, then affix the pump on the engine. • Make sure that the pump lever is correctly aligned with the camshaft lobe. Otherwise, the pump may breakdown when the engine is cranked. • Reconnect the fuel lines, being careful not to overtighten them. • Crank the engine and check for leaks. If the fuel pump is installed correctly and there are no problems, then the engine should start and function normally. • The fuel filter should also be replaced and if the old filter is plugged in, it may be necessary to clean the fuel tank or to replace if it is rusty inside. • Replace gaskets after examining. Tighten the bolts gradually and ensure that they are not overtightened. Is it the fuel causing the problem?
Once the fuel has been excluded as one potential cause of the problem, the most common issues include a leaky or ruptured diaphragm, faulty diaphragm spring and failed check valves. • If the engine delays during acceleration after being idled for long time or by short engine blockade, then the vehicle may be experiencing vapor lock. Other symptoms may include no accelerator pump discharge, lack of fuel pressure etc. • If, after filling the tank with gas, the engine jerks or lags continuously during acceleration and then drop off, fuel foaming could be the cause. Foaming of fuel happens when cold gas comes in intercourse with the hot carburetor. This condition may show up symptoms such as normal accelerator pump discharge and fuel pressure, black exhaust smoke, wet carburetor air horn. • Also, fuels that contain alcohol or octane boosters may change its volatility which can lead to hard starting. Presence of alcohol can lead to corrosion throughout the fuel system thus resulting in fragments that clog the fuel filter and alter the fuel mixture. Checking the fuel pump operation
Now that after creating a safe working environment, below are few ways to check the mechanical pump. • Examine the fuel pump visually. If the fuel is leaking, the diaphragm is damaged and you need to replace it with a new pump. • Remove the air cleaner. Having a look at the carburetor throat, pump the throttle linkage. Any working fuel pump will spatter the fuel into the carburetor. In case if no fuel appears, then checks whether the tank has gas and also both the fuel filter and fuel line for blockages. • Check the fuel pump pressure. Attach a pressure gauge either to the pump outlet or the fuel line at the carburetor, then crank the engine. If there is low pressure than the specifications, then the pump should be reinstated. • Disassemble the fuel line from the carburetor and put it in an empty container. Crank the engine and check how the fuel flows from the fuel line. If you can see strong, steady spurts, then it indicates that the pump is in good working condition and with weak stream then it could block fuel line, clogged fuel filter, empty gas tank or a failed pump. Most modern vehicles come with electric fuel pumps, but owners who work with classic models or older cars must be familiar with the mechanical fuel pumps mechanism. Airtex Fuel Delivery Systems is the leading aftermarket supplier of mechanical and electric fuel pumps and modular reservoir assemblies. For over 50 years, Airtex electric fuel pumps have been the benchmark fuel delivery components for leading companies in the automotive aftermarket. If you are looking for either an electric fuel pump or a mechanical fuel pump, visit us at: