gas tank ?

[Wicked Wolf Auto]

I'm going to be dropping my tank in my 76 K5 for a shackle flip soon and a TBI swap is in the near future as well. Can I put an EFI tank in while I'm at it and still run carbed? If so can I use the old sending unit or will I need to use the one for an EFI tank?

 

[Greg72]

I'm curious about this too.

Need to swap out a stock tank anyway, and I could buy an EFI-ready tank with the extra lines, etc. I think the sender will work either way (0 - 90 ohms) but I wonder if it's valid to just "block off" the extra fittings that aren't needed for EFI until I do that swap later on???

 

[Fordum]

Unless I am mistaken, Chevy EFI works like a Ford's.
The gas does not just pump up to the injector and stop, it circulates back to the tank.
This is because an injector calls for gas pretty much instantaneously instead gradually like a carb.

You have a fuel pressure regulator after the injectors that block the return line up to a certain pressure and let the rest flow back to the tank.

This way, the gas is always moving, and does not have to start from a dead stop to flow into the injector. The fuel pump does not have to spin up from being stalled, and you get gas fast.

However, you could install the return loop, with the regulator, from a junker. You could then tap off between the pump and regulator with a line containing a second regulator set to carb pressure and have a working setup.

But by all means, wait for someone who is a heck of a lot more knowledgeable bout these systems to comment on this answer before ordering parts....

I am really stretching the limits of my knowledge on this one, but it sounds good to me.

Oops, just realized that if you do this, you will need to grab a kill switch off the newer truck too.
In a wreak, the engine driven pump stops with the engine.
In an EFI setup, the fuel pump keeps pumping as long as it has power. It would not be good to be pinned in a wreak and hear the faint whine of the pump in the tank and feel cool gas running down your neck.

 

[Greg72]

My curiousity was more about just using the mechanical pump on the engine for now, and whether I could draw fuel from the EFI tank with the stock pump?

When it came time to hook up my EFI of course I would go ahead and to all the extra work of running return lines, adding the electric pump, regulator and such..... really, I am just looking for a "quick and dirty" way to run my existing carb/pump setup from an EFI tank if such a thing is even possible.

Sorry if this is taking the thread too far away from the original topic.

 

[Wicked Wolf Auto]

My curiousity was more about just using the mechanical pump on the engine for now, and whether I could draw fuel from the EFI tank with the stock pump?

When it came time to hook up my EFI of course I would go ahead and to all the extra work of running return lines, adding the electric pump, regulator and such..... really, I am just looking for a "quick and dirty" way to run my existing carb/pump setup from an EFI tank if such a thing is even possible.

Sorry if this is taking the thread too far away from the original topic.

you're right on track with what I'm wanting to do as well

 

[Fordum]

My gut instinct says it won't work, but I have been eating a lot of fiber lately, so that may just be gas.......

It looks like you would have to suck it through the inop in-tank pump.
Its an impeller type pump, so no valves. But, given the clearances the gas may have to spin the pump to get out.

It seems obvious there would be some blockage by the pump, but if it is as much as a dirty sock, or way more is hard to say.

To be honest, unless someone has already tried it, I think the only way to be sure is with a test.
Given how much work goes on on these trucks on a day to day basis, odds are someone here has, or will have soon, an EFI tank out.

All we need is to get them to hook a hand vacuum pump to the output, or a long clear hose they can suck on to see if it works.

J.

 

[Greg72]

Option #2 might then be to block off the mechanical pump and run the factory EFI tank with it's electric pump....and "Might As Well" run the return line now as well.

The only gotcha at that point would be to regulate the fuel pressure WAAAY down from whatever EFI puts out (20 - 40psi?) to more like 6 psi that a regular ol' carb wants???

I was trying to avoid the extra work, but it might not be terrible....and the conversion to EFI later on would be a few steps simpler if the lines get run now.

 

[Wicked Wolf Auto]

so putting a complete EFI tank with in tank pump and sending unit will fit in my 76? What about the filler neck? if thats the case I'll just snag one of those from the salvage yard and do it when I do the TBI swap.

 

[Greg72]

Some of the message forums that talk about this mention that the filler neck sometimes needs to be cut and re-welded to match the factory position on the older trucks.... otherwise, it can be a pretty simple swap.

The only other consideration for me is ground clearance. I'd rather have a wide and long tank that's shallow, than one that is shorter (Front to back) but hangs down too much. There are a lot of different shapes out there to choose from so that gives us lots of options.