Seeking edgeucation about the in cab EEC fuel tank system.

[71CHEVYSHORTBED402]

Decent write up here: http://what-when-how.com/automobile/...ms-automobile/

Some questions though.

1. The vent pipe assembly for lack of better term hangs from the cab's RH rear pocket. By chance is that a liquid-vapor separator, part of, or? Perhaps it's just a way to connect the fuel tank to the charcoal can.

2. The filler neck takes a hose connected to the top LH side of the fuel tank. Is that for the overfill limiter?

3. The above link reads:

most EEC caps "are incorporated with built in pressure-vacuum relief (Fig. 17.20), so that a vacuum lock may develop due to the fuel expansion or contraction.

and;

"The cap vents excess fuel tank pressure to the atmosphere in case the vapor delivery line is blocked"


3A. I've read the caps don't actually vent or perhaps some do, varying by year I suppose, 70 & 71 Vs 72. Clarification appreciated.

3B. My 1971 C10 NOS cap reads "VACUUM PRESSURE". Does that imply it's filling the tank with air as fuel is used and/or it's a pressure vacuum relief so that vacuum lock develops for fuel expansion or contraction as stated above?

3C. GM installed charcoal cans for the EEC system. Why would the cap need to vent considering the tank vented to the charcoal can? Seems to me this NOS cap doesn't vent.


Thanks

For what worth, fuel return lines weren't installed until 1972, though I suppose some 1971 had them. Some believe A/C systems or something like required a return line, but they weren't installed in 70-71 regardless of AC. In other terms, the fuel pumps and senders on the 71 and earlier had one tube each, the 72 models had two. A return line might make a difference for what cap was used, couldn't tell you. My cap is specifically for a 1970-71 C10 EEC system.