Mechanical fuel pump help

[Astre-mutt]

I'm tired of the poor fuel supply from the stock Astre fuel pump. So I thought I'd try a factory mechanical pump for now. I need some info on the third connection. I assume it has something to do with smog, but not sure. Can I block this off, or do I need to hook it to the return line to the gas tank? The pump was listed as a 85-86 Chevy 4.3L V6.

[spyder_xlch]

It's a return line. I don't know if it can be blocked off or not. You can buy the same pump without the return line. I would trade it in if you didn't use it yet. I've used the 2 line pump where a 3 line pump should have been and just didn't hook the return line up but never did it the other way around (like you have).

[Astre-mutt]

Not going to be able to return it. Won it on eBay for $9.99 + 10.30 shipping. $20.29 for a new Kem fuel pump didn't seem bad deal at the time. Could have gotten a Small Block Chevy pump, but thought it would be smarter to get one for my particular engine & year. Not to smart after all. Only good thing so far, is the fact I won it on Sat, and it was in the mailbox Mon.

So the third line is a return line? Does this act as a pressure bypass? Isn't there a return line in my car now?

[spyder_xlch]

Just run the return line to a "T" fitting and run both lines after the "T" to above your rear wheels. Any fuel that gets returned will help with burn outs. And you'll probably waste as much fuel as if you had 2 quads on your car.
But seriously, I don't think you'd have a return line on your car if it came with an electric in tank pump. I would block off the return nipple and see what happens. It should work just like a pump without the return nipple.

[Astre-mutt]

Cool Matt, I always wanted duel quads, so I could do fiery burnouts. Actually I think I may have found the problem. I found out that the line that runs along the side of the fuel line is a vent line. This thing is blocked solid. No amount of pressure, or vacuum could unclog it. Evidently the gas cap isn't vented ether. So I toke the cap apart, and drilled a 5/64" hole in it. Now it's a vented cap. Just got done so not sure if it fix the problem, or not.

This does explain a lot though. The amount of fuel that runs into the fuel filter is way more then I could use at wide open throttle. So it always confused me how I could run out of fuel at certain times even under mild acceleration. Just at 1 to 1.5 pounds of vacuum would make a fuel system running 2 pounds of pressure almost useless.

[peterpan]

a new small block fuel pump is around 20 bucks so you didn't do to bad on that one

i don't see why a small block pump wouldn't work on a 4.3

[Astre-mutt]

As far as I know there is no difference in the pumps, as long as it has the same pump arm. I had a choice of the small block, or V6 pump from the same company. The V6 pump was for the exact year as my engine, the small block was not. I was being a little pussy, and didn't take a chance with the small block pump. Bottom line I'm sure the SB pump would have been better for my car. (never noticed the third line on the pump)

But back to where I'm at now. Drilling the vent hole in the cap made a difference. I had to drive the car hard before there was a fuel problem now. So it's still not right yet, but much better. When I installed the lower control arms I notice something rattling around in the tank. I plan on dropping the tank this weekend, and seeing what going on in there. If there's something restricting the electric pump, I'll fix it. If not then I'll go ahead with the mechanical pump.

Below is what I did to make the gas cap into a vented cap. Disassembled the cap, and drilled a 5/64" hole in it. When reassembled it would be hard for water, or dirt to get in the tank.