There are two types of fuel tank caps that are available: vented and non-vented.
A non-vented cap will cause fuel feed problems if your fuel tank is not vented. So you must use a vented gas cap, otherwise it will put a strain on the fuel pump, particularly compact solid state electric fuel pumps will fail in no time. Vented caps let in air to take up the used fuel and relieve internal pressure build up in non-vented tanks. Use the correct cap for your particular model.
Vented systems are ones that vent fuel fumes to the outside air thru either a vented cap or vented tank.
Modern closed
systems are ones that reuse the vapors that fuels put off by
recirculating it back into the fuel system by ways of an inline purge
valve, or a type of a carbon canister system, or any other means in a
closed system thru an internal fuel vent. In 1970, Cortina MK2 in North
America came with non-vented caps for a closed evaporative emission
system.
Below is a list of English Ford vented and non-vented caps:
100E series: Non-vented tank. Vented caps: EOA-9030 or Locking cap: E493A-9030.
105E series: Non-vented tank. Vented caps: 105E-9030A or Locking cap: 105E-9030
105E Estate: Vented tank. Non-vented caps: 400E-9030A or Locking cap: 400E-9030B
307E series: Non-vented tank. Vented cap : 307E-9030.
109E Capri / Classic Consul. Vented tank. Non-vented caps: 204E-9030A or Locking cap: 204E-9030B
EOTA / ETTOA: Non-vented tank. Vented caps: EOA-9030 or Locking cap E493-9030.
204E / 206E: Vented tank. Non-vented caps: 204E-9030A or Locking cap: 204E-9030B.
211E / 213E: Vented tank. Non-vented caps: 204E-9030A or Locking cap: 204E-9030B.
Cortina MK1 sedan: Vented tank. Non-vented caps: 400E-9030A or Locking cap: 400E-9030B.
Cortina MK1 Estate: Vented tank. Non-vented caps: 113E-9030A or Locking cap: 3014E-9030C
