TECH TIP - Reprinted from the March 2000 Midwest Fieros Club Newsletter

Fuel Pump Problems-

Q. The fuel pump on my 1985 SE V6 failed at 53,000 miles and I had it replaced at a local dealership. Since then, I have had two more fuel pump failures in only 11,000 miles. Are the replacement pumps inferior? Or is the dealership mechanic doing something wrong?

A. As far as we know, there is no problem with GM replacement fuel pumps for the Fiero. In our opinion, the dealership is not installing your replacement fuel pumps incorrectly, but their mechanic may not be doing everything needed to insure against premature fuel pump failure.
Here's why. Whenever a fuel pump fails, it is wise to do at least two other service procedures: (1) change the fuel filter (Haynes manual, p. 47), and (2) change the vapor recovery canister filter.
Most people know about the fuel line filter, but few know about the vapor recovery canister filter. Why should both filters be changed? Because both filters can cause the fuel pump to work harder than necessary, heat up, and fail prematurely. It is fairly obvious that if the fuel line filter is clogged, the fuel pump has to work harder to overcome the obstruction. But exactly what is the vapor recovery canister and how can it affect the fuel pump?
The vapor recovery canister is a part of the fuel system that keeps gasoline vapors from escaping into the atmosphere when the engine is not running and is a required part of the Federal Clean Air Act. It is connected to the fuel tank, throttle body, intake manifold, and among other things, allows expansion and contraction of the gas vapor in the fuel tank to occur without releasing hydrocarbons into the atmosphere.
It performs this function by allowing air to pass freely through the canister while trapping hydrocarbon vapors, which are absorbed into activated charcoal granules in the canister when the engine is not running. When the engine is operating, air is drawn through the canister from the atmosphere, and hydrocarbon vapors are swept out of the activated charcoal and burned with the rest of the fue1. The amount of hydrocarbons burned in this manner is exceedingly small and does not affect the air to gasoline ratio.
The canister filter is found at the bottom of the canister and is needed to keep airborne dust and other particulate material out of the charcoal bed. If the filter becomes severely clogged, air cannot pass freely through the canister to the fuel tank. When the engine is running and gasoline is being pumped from the tank, an equal volume of air replaces the volume of gasoline leaving the tank, or else a slight vacuum would be produced in the fuel tank. If this happens, the fuel pump must work harder to overcome the vacuum. In a worst-case scenario, the fuel pump will not be able to overcome the vacuum and the engine will starve for gasoline and stop. While this occurrence is very rare, premature fuel pump failure because of a clogged canister filter is more common. To avoid the problem, follow the procedure given in Haynes (p. 165) and inspect the filter. If it appears dirty, change it. It's a very simple, inexpensive, maintenance procedure that can save you the cost of a fuel pump replacement. To keep your vapor recovery canister operating properly, do not top off your tank when you fill it, otherwise gasoline might run down the vent line into the canister and flood the charcoal bed. This could render it inactive.

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