Replacing Mechanical Fuel Pumps

Replacing Mechanical Fuel Pumps

The heartbeat of any vehicle

Fuel pumps fall into two camps: electrical and mechanical. Contemporary autos, being fuel injected and subject to complicated electronic engine management controls, use electric fuel pumps. Generally, these are manufactured to last the lifetime of the vehicle-which is not to say that professional mechanics don't have occasion to change them. Clogged fuel filters cause back pressure that can burn the pumps out, and if you stop to think about where all that crud in the fuel filter has been, you'd quickly sympathize with a pump's plight. Electric pumps also tend to be located in remote places-such as inside the fuel tank-so if replacement is needed, take the vehicle into the shop.

Those of you running carbureted classics have mechanical fuel pumps. These provide fuel to the carb thanks to an eccentric on the camshaft. The pump is connected to the fuel tank via an inlet line made of flexible hose, affixed with a hose clamp. A steel line usually runs from the pump to the carb, connected by a tube fitting. Some pumps also use a vapor return hose.

Don't start the job until you've completely read these instructions.

Gather Together

> A ratchet wrench set that boasts a universal joint.

> Open-end wrenches.

> Pliers or a screwdriver for the hose clamp.

> Some means of plugging the fuel line from the gas tank, such as a wooden dowel, hemostat or a bolt.

> Jackstands or drive-on ramps.

> Gasket sealer or cement.

> The appropriate fuel pump and gasket specific to your vehicle and engine.

Installing the Fuel Pump

> First, install a new fuel filter (see article elsewhere on this site).

> Disconnect the battery ground cable.

> Check out the fuel line running from the tank and replace if it's leaking or cracked.

> If you insist on replacing an electric fuel pump yourself, read your service manual carefully, because chances are the fuel system is operating under high pressure, requiring you to take appropriate precautions.

> Undo the hose clamp on the old pump connecting it to the fuel tank, and pull off the fuel tank hose. Plug it with the dowel, bolt or hemostat to prevent fuel leakage.

> Using a wrench on the fuel pump fitting and another on the line nut, unfasten the outlet line to the carburetor.

> Unscrew the two fastening bolts and remove the old fuel pump. Should any old gasket material remain on the block's mounting flange, scrape or wipe it off.

> Using gasket sealer or cement, coat both sides of the new gasket. Slip the attaching bolts through the new pump and slide the gasket over them into place.

> Mount the pump on the engine, checking that the pump's rocker arm is situated against the eccentric in the engine, or that the actuating pushrod is correctly fitted to both the fuel pump and the engine.

> Attach the outlet line running to the carburetor to the new fuel pump. This job, potentially tricky, can be made easier by disconnecting the line at the carburetor, attaching it to the pump first, and then back to the carb. Use a pair of wrenches to secure the pump fitting and to tighten the line nut.

> Clamp on the fuel return hose and, if present, the vapor return hose. Make sure all clamps are tightened.


> Reconnect the battery ground cable.

> Start the engine and immediately check for leaks.

Installation Tips

> Make sure all of your supplies and tools are close at hand before starting the job.

> Take your time, don't hurry, and should fuel start to spurt, stay calm.

> Raise and secure the vehicle properly using jackstands, tire chocks and the vehicle's parking brake, as necessary.

> Make sure your hands are thoroughly clean before handling the new pump.

> A repair manual specific to your vehicle may provide valuable details that this article cannot address.

> If the car hasn't cooled adequately, wait, and in the meantime, beware of hot objects.

> If safety glasses are not available, do not perform this installation until you get a pair.

> Again, it's a good idea to replace the fuel filter when doing any fuel system work, whether it is to an injected or carbureted vehicle.

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