Ford 1997 Aerostar Workshop Manual page 3

1997 Aerostar/Ranger
Section 10-01: Fuel Tank, Filters, Lines and
Electric Fuel Pump
DESCRIPTION AND OPERATION
Fuel Tank Filler Cap
NOTE: Use of an aftermarket fuel tank filler cap (9030) other than an authorized Ford/Motorcraft
service part could result in damage to the fuel system or improper system operation if not properly
designed/manufactured for pressure vacuum relief. Customer warranty is void for fuel tank and/or
fuel system damage resulting from the use of such fuel tank filler caps.
The fuel tank filler cap is designed to seal in fuel vapors, reducing unburned hydrocarbon emissions, while
allowing air to enter as fuel is used. It is also designed to relieve high pressure inside the fuel tank (9002)
due to fuel expansion and vaporizing because of high ambient temperature. The fuel tank filler cap has a
built-in pressure/vacuum relief valve to achieve this. The valve opens to allow air to enter at -3.44 kPa (-0.50
psi, -1.0 in Hg). The valve opens to relieve pressure at 12.4 kPa (1.8 psi).
Fuel tank filler cap relief only operates when the fuel vapor canister cannot handle vapor adequately to
preclude pressure buildup.
Air must enter the fuel tank as fuel is used because the fuel leaving the fuel tank would create a partial
vacuum which could become strong enough that the fuel pump (9350) could not overcome it, causing fuel
starvation. Also, air pressure on the outside of the fuel tank could collapse the fuel tank.
If pressure from fuel expansion and vaporization were to rise too high, the pressure could bulge the fuel
tank, blow off hoses, and cause seals to leak. The risk would be greatest on a hot day when the fuel tank
was filled with fuel from a cool underground storage tank. Normally, positive fuel tank pressures do not rise
high enough to open the valve so fuel vapor can only escape via the vapor valve and tube to the charcoal
evaporative emissions canister (EVAP canister) (9D653) and, ultimately, the engine (6007). Refer to
03-13 .
The fuel tank filler cap is secured to the vehicle by a nylon tether to prevent loss during refueling.
file://C:\TSO\tsocache\VDTOM_5368\SVK~us~en~file=SVKA1003.HTM~gen~ref.HTM
1997 Aerostar, Ranger, Equipped with 2.3L, 3.0L, and 4.0L
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Gasoline Engines Workshop Manual
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2011-04-29