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.