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Old 04-23-2020, 04:19 PM
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Cliff Cliff is offline
327 Rambler
 
Join Date: Mar 30, 2002
Location: Upper East Tennessee
Posts: 718
Non-Vented Fuel Tank

My 77 Cherokee has no fuel tank vent system. After a drive on a warm day the tank builds pressure and opening the fuel cap allows the pressure to escape. I assume this is common since the gas caps sold by BJ's actually have a pressure warning on the cap.

At some point this pressure has to cause problems. A long drive on a hot day must build lots of pressure. It used to be that cars had vented gas caps before manufactures turned to vent lines and charcoal canisters. Is this a common problem with FSJ's in general, and not a big deal?
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Old 04-23-2020, 06:15 PM
wiley-moeracing wiley-moeracing is offline
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Join Date: Feb 15, 2010
Location: arizona
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you need a vented fuel cap.
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Old 04-24-2020, 03:40 PM
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tgreese tgreese is offline
 
Join Date: May 29, 2003
Location: Medford MA USA
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No vapor recovery in 1977 for full-sized Jeeps delivered in the 49 states. California cars and trucks had it. This is shown in the online TSM for 1977, free to read and download. Jeep took advantage of the rules and made the GVWR for all the FSJs above 6000 in this era. The rules were more lax for heavier rated vehicles then.

Yes, you need a vented cap. I use a locking cap that came with my '77. It may or may not be intentionally vented, but it's loose enough now that it does not matter.
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Maine beekeeper's truck: '77 J10 LWB, 258/T15/D20/3.54 bone stock, low options (delete radio), PS, hubcaps.
Browless and proud: '82 J20 360/T18/NP208/3.73, Destination ATs, 7600 GVWR
Copper Polly: '75 CJ-6, 304/T15, PS, BFG KM2s, soft top
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Old 04-25-2020, 01:34 AM
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FSJunkie FSJunkie is offline
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Join Date: Jan 09, 2011
Location: Not The Hot Part, Arizona
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That is so crazy. I can tell you that every 1972 Jeep, even down to the CJ5, had a vapor recovery system. Some used canisters and some just vented the gas tank into the engine crankcase, but they all had a sealed fuel tank. The GVWR thing came along later. It's just comical.
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