Chevy/GM Truck Fuel Sending Units

Greetings All,

Can anyone explain the purpose of the multiple outlets on Chevy/GM fuel sending units?

My 1975 3/4 ton has dual tanks with 2-outlet sending units. I have salvage tanks and sending units from a 1985 model truck that has 3- outlet sending units.

The salvage units and the drivers side unit on my truck are working. The passenger side on my truck is unknown. It may work, but if not I'd like to use the newer units on both. The passenger tank and sending unit have been disconnected and non-functional since before I owned the truck (many years).

Are the newer sending units likely to have the same resistance range as the older ones?

Thanks in advance, Tom

Reply to
tom_murphy
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Do you mean the fuel lines? One is a fuel outlet line. One is a fuel return line. The last is likely a vent line that connects to the charcoal canister to collect the vapor from the tank.

Your 75 has one fuel line and one return line.

Reply to
Steve W.

Don't recall a fuel return line on 75 Chevy trucks. That would mean there would be 3 places on the mechanical fuel pump to hook lines, and those pumps were around mid/late 60's to early 70's. Some 327, 350

4BBL small blocks, and some big blocks.

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Reply to
thenitedude

Oops. Here's one for a 75 with a 454:

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Reply to
thenitedude

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Some attached to the pump and others attached to the filter. It could also be a vapor line depending on the vehicles original build. I don't get to work on those much. The only 70s vintage around here now don't have anything remotely stock in the fuel systems...

Reply to
Steve W.

Back then , Chevy filters were in the carb, right where the line connects. No extra line coming off.

Reply to
thenitedude

IIRC a '73 Chevy pickup had two hose fittings on the fuel pump; one was the suction and one was a return back to the tank. I never had a reason to drop the tank on my dad's truck, so I can't say what the sending unit looked like, nor do I recall if it has a charcoal canister or not.

nate

Reply to
N8N

On my truck both tanks have a short stubb of hose attached to the 2nd outlet. The hose has a small plastic fitting on it which appears to be a one-way vapor valve or something like that. It looks factory.

Also, the resistance range I'm getting on the "good" sending units is about 15 ohms empty and about 125 full. I thought it should be 0 - 90 ohms.

Any comments?

Thanks!

Tom

Reply to
tom_murphy

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