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11-11-2015, 03:11 PM | #1 |
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Join Date: Sep 2015
Location: Pottsville, Pa
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Fuel sending unit questions
I have a 79 k20 with a single tank on passenger side. I replaced my fuel and sending unit. I replaced the 2 line sending unit with a new 2 line sending unit. I did fine a third line on my frame which is for the vent. So the person that had it before switch to a two line sending unit. My question with setup work or will the tank not vent through cap. I already had the two line in not seeing the third line on the frame. So if I have to change it I will.
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11-11-2015, 04:48 PM | #2 |
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Re: Fuel sending unit questions
If you have a vented cap it'll work fine.
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
11-11-2015, 09:12 PM | #3 |
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Re: Fuel sending unit questions
I have the old style that is not a threaded. I'm pretty sure it is not vented.
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11-12-2015, 12:33 AM | #4 |
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Re: Fuel sending unit questions
If there's no vapor line I believe you need a vented cap...
That being said. I was unaware there were light trucks built after 1974 with no vapor line. GM made em with no return line but I thought they all had vent lines. I also reserve the right to be full of hooey... Are you positive the two lines are feed and return and not feed and vapor?
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
11-12-2015, 03:13 PM | #5 |
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Join Date: Sep 2015
Location: Pottsville, Pa
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Re: Fuel sending unit questions
I have a supply, return and vent line on frame. The vent line goes to a black charcoal canister. So im pretty sure who had this truck before me screwed up.
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11-12-2015, 06:23 PM | #6 |
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Location: Tucson, AZ
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Re: Fuel sending unit questions
3/4 trucks were considered heavy duty for emissions purposes and had a short hose off the third nipple with a one way vent cap - same as the vent cap on the differential vent. On my 83 C20, I ran the vent lines back to the rear bumper area so I would not smell gas vapors in the cab. 1/2 tons all had charcoal canisters, as far as I know.
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11-12-2015, 07:57 PM | #7 |
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Re: Fuel sending unit questions
When there's a return line from the fuel pump there are three hose connections on the sender. Vapor, Return, and Supply.
The 2 hose senders are Vapor and Supply. I don't believe GM used vented gas caps on these trucks.
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
11-12-2015, 09:36 PM | #8 |
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Re: Fuel sending unit questions
So only having two lines is incorrect. Since my cap cannot vent.
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11-13-2015, 01:18 AM | #9 | |
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Re: Fuel sending unit questions
Quote:
I bet the emissions drones would have a fit if you added it without permission. Ignore the bowl vent line in this diagram. The purge valve control hose is on ported vacuum and the purge hose feeds to the PCV vacuum hose. If you want to be real fancy put in a thermo-vacuum valve in between the purge valve and the ported vacuum. I believe so. If you have three hoses then you probably need the three nipple sender.
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. Last edited by hatzie; 11-13-2015 at 01:26 AM. |
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11-13-2015, 08:22 AM | #10 |
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Join Date: Jul 2007
Location: Tucson, AZ
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Re: Fuel sending unit questions
On the negative side, a charcoal canister will eventually plug up and need replacement. Gas smell is an issue, but cars were parked in garages long before charcoal canisters existed. One poster here just ran a vent line to the air cleaner and let the carburetor burn the gas vapors.
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11-13-2015, 09:10 AM | #11 | |
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Join Date: Oct 2008
Location: Wentworth, NH
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Re: Fuel sending unit questions
Quote:
It's a convenience feature. Mitigating the petrol fumes is more for keeping peace with SWMBO...
__________________
1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials...
And please let us know if and how your repairs were successful. |
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11-13-2015, 06:32 PM | #12 |
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Join Date: Sep 2015
Location: Pottsville, Pa
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Re: Fuel sending unit questions
Thank you everyone for your help. I'll see what I can come up with tomorrow.
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