Fuel Tank Pressurization

Joined: 5:19 PM - Jun 15, 2004

5:27 PM - Aug 09, 2017 #1

while trying to extract my Mustang from hibernation, I have run into a problem with the fuel tank pressurizing. After a short run or even without running, the tank pressurizes. At its worst, it gets high enough to force gas past the fuel pump to the point where there will be enough gas forced out to fill and hydrolock a cylinder. This is a stock 72 fuel system with the evaporative system removed although the hard lines and vapor separator are still there. There is an audible whoosh when the pop open cap is opened virtually every time the cap is opened.

I have not yet tried installing a different vented cap to eliminate that possibility. Based on the information that I have been able to find, it seems that whether the cap is venting or not, the pressure should be able to vent through the vapor separator in the top of the tank. Make sense? It seems implausible that both the separator and the cap would not vent. Can the pop open cap be taken apart and inspected/cleaned? This is the cap with the seal, not the separate cap under the "popper". Anyone else run into this problem?