Tyler Posted March 27, 2021 Share Posted March 27, 2021 We just had our first 90 degree day here in Georgia and I drove the truck about 110 miles. Went to get gas and the cap nearly came out of my hand when the tank vented. I've had the truck for several years, even drove across country and this has never happened. However, this IS the first hot weather day since installing Holley FI. I thought the roll-over valve would have kept the tank vented for small pressure changes. Some insight or knowledge upgrade would be appreciated, thanks! Link to comment Share on other sites More sharing options...
Gary Lewis Posted March 27, 2021 Share Posted March 27, 2021 If the vent hose that connects to the rollover valve is plugged it can’t vent. I’d check the hose. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 27, 2021 Share Posted March 27, 2021 First. after 1986 Ford started using larger tank vent systems, probably since everything was going to be EFI by 1988 and EFI returns warm to hot gas to the tanks resulting in more evaporation. The over 8500 GVW trucks do not use a sealed system even with EFI as recently as the last of the OBS trucks in 1997. Maybe first check that nothing is obstructed on your vent system. Link to comment Share on other sites More sharing options...
Tyler Posted March 29, 2021 Author Share Posted March 29, 2021 First. after 1986 Ford started using larger tank vent systems, probably since everything was going to be EFI by 1988 and EFI returns warm to hot gas to the tanks resulting in more evaporation. The over 8500 GVW trucks do not use a sealed system even with EFI as recently as the last of the OBS trucks in 1997. Maybe first check that nothing is obstructed on your vent system. Thank you both. I'll get under there and give that hose a look. Link to comment Share on other sites More sharing options...
kramttocs Posted March 29, 2021 Share Posted March 29, 2021 Thank you both. I'll get under there and give that hose a look. I agree on checking the vent but I just wanted to mention that the 460s (I believe only them) had a gas tank cap that has two levels of tabs. The cap also has a pressure warning on it. With the two levels of tabs and pressure it would vent on the first twist but wouldn't blow the cap off. I could see the 460s having more vacuum but not sure why they'd have more pressure (Bill?) than any other carbed config. Reason for mentioning it is (if the vent is clear) maybe the conditions that prompted Ford to put these on 460s is being met with your setup somehow. Link to comment Share on other sites More sharing options...
85lebaront2 Posted March 29, 2021 Share Posted March 29, 2021 I agree on checking the vent but I just wanted to mention that the 460s (I believe only them) had a gas tank cap that has two levels of tabs. The cap also has a pressure warning on it. With the two levels of tabs and pressure it would vent on the first twist but wouldn't blow the cap off. I could see the 460s having more vacuum but not sure why they'd have more pressure (Bill?) than any other carbed config. Reason for mentioning it is (if the vent is clear) maybe the conditions that prompted Ford to put these on 460s is being met with your setup somehow. The hot fuel handling package did essentially what an EFI system does, hot fuel from the engine compartment is returned to the in-use tank creating a fair amount of vapor pressure. Ever tried to find a locking gas cap for one of these? Link to comment Share on other sites More sharing options...
Tyler Posted March 29, 2021 Author Share Posted March 29, 2021 The hot fuel handling package did essentially what an EFI system does, hot fuel from the engine compartment is returned to the in-use tank creating a fair amount of vapor pressure. Ever tried to find a locking gas cap for one of these? Perhaps my roll over valve is too sensitive and shuts when the fuel heats up. Maybe I could gut it and buy an aftermarket remote unit to install at the end of the hose. Link to comment Share on other sites More sharing options...
Rusty_S85 Posted March 30, 2021 Share Posted March 30, 2021 We just had our first 90 degree day here in Georgia and I drove the truck about 110 miles. Went to get gas and the cap nearly came out of my hand when the tank vented. I've had the truck for several years, even drove across country and this has never happened. However, this IS the first hot weather day since installing Holley FI. I thought the roll-over valve would have kept the tank vented for small pressure changes. Some insight or knowledge upgrade would be appreciated, thanks! Interested to see what you find out. I have a '82 that I planned on keeping the OE vapor canister system but if it ends up being a difference be nice to know so I can make the changes then vs waiting till later on. Link to comment Share on other sites More sharing options...
Tyler Posted April 2, 2021 Author Share Posted April 2, 2021 We just had our first 90 degree day here in Georgia and I drove the truck about 110 miles. Went to get gas and the cap nearly came out of my hand when the tank vented. I've had the truck for several years, even drove across country and this has never happened. However, this IS the first hot weather day since installing Holley FI. I thought the roll-over valve would have kept the tank vented for small pressure changes. Some insight or knowledge upgrade would be appreciated, thanks! Interested to see what you find out. I have a '82 that I planned on keeping the OE vapor canister system but if it ends up being a difference be nice to know so I can make the changes then vs waiting till later on. As of today I haven't had any more issues. Perhaps the fuel sloshed around perfectly enough to cause the rollover valve to shut and it stayed that way until I removed the fuel cap. I'll keep my eye on it. Getting a little over 13 MPG at 70 mph by the way. Thank you for the replies. Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 2, 2021 Share Posted April 2, 2021 As of today I haven't had any more issues. Perhaps the fuel sloshed around perfectly enough to cause the rollover valve to shut and it stayed that way until I removed the fuel cap. I'll keep my eye on it. Getting a little over 13 MPG at 70 mph by the way. Thank you for the replies. Good deal! But 13 MPG @ 70 is nothing to write home about. Do you have more tuning to do? Link to comment Share on other sites More sharing options...
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