Checking a mechanical fuel pump


Here you can get Mechanical Fuel Pumps Work and Checking Fuel The Pump.

If a car stops and has not run out of petrol, check whether there is petrol in the carburettor. If there is not, there is a fault in the fuel system.

Disconnect the fuel line to the carburettor, slipping a plastic bag over the end of the line as you do so to catch any fuel inside. Secure the bag with a rubber band, then turn the engine over with the starter. If fuel spurts out, there is a carburettor fault. If no fuel, or only a dribble, emerges, either there is a blockage or leak somewhere in the fuel line or the fuel pump is not working. Some pumps are sealed and cannot be repaired; check to see if there are screws for dismantling.

A mechanical-pump drive hardly ever fails — though signs of wear may appear on the cam and operating lever, linkages and pins. Diaphragms can leak. A small leak may affect the engine noticeably only at high speeds, but may also let petrol drip through into the camshaft area and from there to the sump . If this occurs, there is a risk of an explosion.

How Mechanical Fuel Pumps Work

Mechanical fuel pumps siphon fuel from the gas tank. It then pushes it to the carburetor whilst the engine is cranking or running. All mechanical gasoline pumps used on inline six cylinder and V8 engines are diaphragm type. No modifications or upkeep are possible.

The pump is operated by an eccentric lobe on the camshaft or the camshaft gear. On six cylinder engines, the eccentric rides directly on the fuel pump arm. On V8 engines, a push rod between the camshaft eccentric and the fuel pump operates the fuel pump arm.

Checking Fuel The Pump

  • Remove the air cleaner. While looking in the throat of the carburetor, pump the throttle linkage. A working pump will squirt fuel into the carburetor. However, if no gasoline appears, confirm the tank has gas and check the gasoline line and fuel filter for blockages.
  • Visually inspect the pump. Inspect the fuel pump visually. If gasoline is dripping, the diaphragm is faulty and also you need a new pump.
  • Another way to check the pump is disconnect the fuel line at the carburetor and location it in a container. Crank the engine to see if the pump is pushing any fuel through the line. Strong regular spurts of gasoline mean the pump is working. No gasoline or a weak stream means a bad pump, a plugged fuel filter, fuel line blockage.
  • You should also check fuel pump pressure. Connect a gasoline pressure gauge to the pump outlet, or tee a gauge into the fuel line at the carburetor. Crank the engine and be aware the pressure reading on the gauge. If there’s no stress, or if pressure is much less than specifications, replace the pump.

Pumps – (Leaking Fuel)

  • Most mechanical fuel pumps have a weep hole on the bottom side of the unit. When the internal diaphragm leaks, fuel escapes via the weep hollow to inform the car owner of a malfunction. This is one of the extra common gasoline pump problems. Usually located on traditional cars among 30 and 60 years old. The inner rubber diaphragm is capable of lasting an extended time. Gas is a petrol product that allows amplify the lifestyles of the rubber diaphragm via lubrication.
  • Another common area for a fuel leak is the hoses that lead from the tank to the gasoline pump. Since the metallic tube is uncovered to the elements, it’s common to look those rusted and leaking. The rubber hose that connects the metallic tube to the gasoline pump also can dry rot and leak. A common mistake is to replace this small phase of rubber hose with any scrap piece. Use the specialized and reinforced rubber gasoline hose on this situation.

Pumps – (Leaking Oil)

  • On many automobiles, the fuel pump actuator arm passes through the timing cover. This arrangement allows the constant rotating motion of the camshaft or crankshaft to perform the arm. That additionally provides another location for oil to leak.
  • Where the gasoline pump mounts to the timing cover a gasket gives a tight seal. Although capable of long term reliability, often engine vibration will motive the bolts on this place to loosen up. When this occurs it’s feasible for oil to seep out across the gasoline pump to timing cover gasket. If the leak maintains lengthy enough, replace the seal, due to the fact the detergents in the engine oil will eventually damage it.

How To Replace Mechanical Fuel Pumps


So, There are holes in the passenger side front of the engine. These holes have been for engines that used the front engine mounts. The top bolt hole aligns with the gas pump push rod and could have a 3/8″ x 3/4″ bolt. This bolt needs to be removed and a longer 3/8″ bolt set up in its place. Some block assemblies are supplied from the factory with a 3/8″ through 7/8″ bolt with (2) thick washers.

This will permit the OEM bolt to be re-inserted with out the washers to secure the rod in place. Once the (2) gas pump mounting bolts are tightened, the bolt securing the rush rod may be removed. They may be re-inserted with the washers under the head thereby preventing contact with the rod however sealing the hole. The longer bolt is to gently keep the fuel pump push rod in the retracted position.


The camshaft has a lobe on it that reasons the fuel pump push rod to move in and out. This is what makes the gas pump actually pump fuel. Total travel of the pump rod is about 0.394′ (10 mm). This lobe needs to be located in this sort of manner that the rod is furthest returned, away from the pump. While this isn’t certainly vital it could make installing the pump a bit easier.

So, with the longer bolt in the upper hole, carefully tighten the bolt till it holds the push rod. It should stop it from sliding back out, bear in mind simply finger tight or you’ll bend or nick the push rod. Remove the gas lines, plug them to prevent dirt from entering. Remove the fuel pump mounting bolts, then the pump. Clean all the way around the fuel pump hollow in the spacer.


Sometimes the hole in the front of the block can not be accessed. An alternative is to remove the spacer plate and push rod and put some heavy grease on the push rod. This grease will (for a while) hold the pushrod to the cam in the retracted position. Reinstall the spacer plate, use a new gasket. With the gasket at the gas pump insert the gas pump arm into the hole in the spacer plate. Once the pump arm is in position, you’ll should push towards the pump’s go back spring pressure. This gets the pump’s mounting holes near sufficient to the spacer to begin the bolts.


Now you will need to loosen the bolt holding the push rod in position so the push rod can move. Furthermore, You may need to rotate the engine a bit to let the fuel pump cam retract the push rod. Tighten the bolts evenly until the pump meets the spacer. DO NOT forget to remove the longer bolt holding the push rod. Replace the original bolt into the same hole, with a little sealer on the threads. Reattach the fuel lines- do not use teflon tape.


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