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Old 01-07-2019, 07:03 PM   #1
Richard
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Default fuel tank question

I have a 77 SII, 4sp, 4cl, 1bbl. I am wondering, are all fuel tanks pressurized, meaning: when taking off the gas cap, I get a big puff of pressure, really big puff. the truck runs just fine, get very good MPG.

I was under the impression that the fuel system is vented and should have no pressure. Please advise?

thanks:
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Old 01-07-2019, 09:47 PM   #2
Scoutboy74
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Default Re: fuel tank question

That's not right. Your vented cap isn't venting.
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Old 01-08-2019, 10:44 AM   #3
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Default Re: fuel tank question

Yep you like have a cap for an emmisions rig and should have one for a vented non emmisions truck.
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Old 01-08-2019, 04:18 PM   #4
Robert Kenney
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Default Re: fuel tank question

A 77 was a smog rig in CA IIRC, and the cap in that case is sealed so as not to allow fuel vapors to pass out of it but it should let air in to the tank.
Do you have a charcoal canister, and vapor recovery system on your Scout?
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Old 01-08-2019, 04:56 PM   #5
Richard
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Default Re: fuel tank question

re:

the 77 4cyl, 1 bbl, is a 50 state "federal" truck. I've just never noticed that there was so much pressure. Should I have a "vented' gas cap,or no ? Like I said, the truck runs fine.

much thanks for the responses.
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Old 01-08-2019, 04:57 PM   #6
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Default Re: fuel tank question

oh, I forgot: no charcoal air canister.
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Old 01-08-2019, 05:47 PM   #7
Robert Kenney
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Default Re: fuel tank question

Do you have an emissions label? Do you have to smog it? If not use a vented cal that allows venting both ways. The pressure indicated that all venting out of the tank is blocked.
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Old 01-08-2019, 08:48 PM   #8
Richard
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Default Re: fuel tank question

well, I haven't seen an emissions label, but that does not mean there isn't one (could be worn off). Yes, I have to have to smog it, in fact, I just had it smogged in December. It passed with no problems (given that the settings were at factory specs).

I was thinking of using a vented gas cap since the one I have on the truck seems to be not vented. By the way, does venting/non venting have anything to do with gas mileage? I figure this subject should go to another thread, but it didn't hurt to ask.

Thank you for the quick responses.
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Old 01-08-2019, 09:21 PM   #9
Scoutboy74
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Default Re: fuel tank question

No, it's gonna suck either way.
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Favorite hobby...Driving Salma Hayek in my Scout

Coal Trickle - '99 Dodge Ram SLT 2500 Q-Cab SWB 4x4 - 5.9L 24V CTD/NV4500/8800# GVWR/12K# winch
Hooty - '74 SII 4x4 - 392/TF727/D20/3.73 D44's/Spartan FA/Krac-lok RA/RC 4" SUA/34x11.5 TSLs/33g Fuel/8K# winch
Lemuel - '73 1210 Reg Cab 4x4 Camper Special - 304/TF727/NP205/4.09 FA25 & 4.10 RA16 - "Pull Lemuel, pull!"
Mongo - '71 1210 Reg Cab 2WD - 345/TF727/4.10 RA17 - "Mongo love candy! Duh, huh, huh!"
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