'78 400 fuel sending unit question - Second Generation Pontiac Firebird (1970 - 1981) - Firebird Nation

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'78 400 fuel sending unit question


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4 replies to this topic

#1 fireforeffect

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  • Model: Trans Am WS6
  • Engine: 400
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Posted 24 May 2020 - 03:39 AM

Bought a new fuel sending unit from Summit before I pulled the tank during a suspension rebuild, my gauge needle was bouncing back and forth at any reading below full. Went to swap the sending unit out yesterday and discovered the one I bought as "Fits your 1978 Trans Am" only has a single 3/8" feed line that goes to the wrong side of the tank (passenger), where my original has what appears to be a 1/4" vapor return (from passenger side) and the 3/8" feed goes to the driver side. Have since tracked down the correct replacement sending unit at Year One, but want to know if it's OK to block off the vapor return line? My EGR is blocked off at the manifold and I'm running an aftermarket Edlebrock carb and intake. If I cap the vapor return line at the tank and at the frame rather than reconnect it w/ the existing hard/soft lines, will I experience any problems? 



#2 myk74

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Posted 24 May 2020 - 04:55 AM

I would probably run a rollover valve on the tank just to make sure the tank was vented. I don't trust vented gas caps



#3 NOT A TA

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Posted 24 May 2020 - 06:11 AM

As Mike referred to, venting would be an issue if you just plug the vapor line. The early 2nd gens used a vented fuel cap but the later ones did not. So if you just plug the line you'll create a vacuum in the fuel tank.


John Paige

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#4 fireforeffect

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Posted 25 May 2020 - 04:53 AM

"Rollover" as in the car rolls over and the check valve prevents fuel from spilling out the vent? Any recommendations on which one to use, or is it just general fit to the end of the open 1/4" vapor return line from the sending unit and secure it upright? 


Edited by fireforeffect, 25 May 2020 - 04:59 AM.


#5 myk74

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  • Transmission: TH400

Posted 25 May 2020 - 02:58 PM

The kind I use takes a bit of hose from the sender to the valve..  I like to mount the valve with a bracket in a vertical position. I suppose zip tying would work as well. Yes, it's just a vent that closes when it goes upside down. I couldn't find a 1/4 inch one, but I imagine you could get a 5/16 hose to clamp down on your sender..  or possibly get the 1/4 hose on the 5/16 valve. I use these...

 

https://www.summitra...m/parts/tnk-vvr






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