Has anyone tried using a mechanical pump and leave the electric pump in the tank? I swapped in a carb'd 350 in a 92 rs with a 3.1L and the carb setup is kind of temporary until I get my lt1 intake finished. Will the mechanical pump be able to pull fuel through the intank pump?

 

Don't think so - never heard of anyone even being able to pull through the intank pump with an external electric pump. Why not just use a block off plate where the mechanical pump is, and use the in-tank pump and get the Mallory 4309 regulator?

 

because its $60-$80

 

Your other option is to drop the gas tank, and replace the intank pump with a pick up from a carb car, or some just run a hose in place of the stock pump. But $80 is much easier than dropping the tank in my world, I've done 2 tank drops and they aren't hard, but time consuming.

 

My '85 will, but I had to hook up a mityvac to the fuel line & build up some suction. Once I did that, it was fine.

 

Some have gotten away with it, but if you plan on making any kind of decent power, or plan on racing the car, forget it.

I only vaguely recall one person doing it, but if you use a stock factory type return mechanical pump, you should be able to use the in-tank electric as a pusher pump. If needed, you could put an inexpensive ($25 Holley) dead-head reg in line with the carb inlet line.

There are some risks worth taking, and some costs worth avoiding, but trying to pull through a non-operating in-tank electric isn't either one of them.

 

just updating this thread for someone else searching in the future. The car does run fine with the mechanical pump pulling through the electric pump. The electric pump is not powered(at the moment). I ordered a holley bypass regulator yesterday, so I will eventually run the stock pump(v6) and remove the mechanical. My plans are to step up to a 255lph pump in the future, but for now I think it is more than enough.

 

Wow I doubt it was that much money. I have a '91 RS that I am currently putting in a carbed 350. I left the fuel pump and just bought a Mallory regulator for cheap. They don't cost much. Then I ordered a fuel pump block off plate from Jegs for cheap as well.

 

How did you cut the power to the fuel pump? I'm doing the same thing you are except my electric pump is still on lol but it still runs fine but I would like to know how to shut it off.

 

well cheap is relative, right? The Holley bypass regulator was $68 from Jegs. If you don't need it and there is a way you can do it without spending more money, why buy the regulator? In my case I wanted to get the car running and driving until I get my lt1 intake finished, so I did not want to spend the money on a temporary situation.

 

I pulled my ecm and wiring harness when I put the carb'd motor in. I assume that is why the pump is not running - I have not verified that.

If your electric pump is running, I would imagine it is not good for it. It is essentially dead heading into your mechanical pump. I am actually suprised it is not forcing to much fuel pressure into the carb.

 

Well for some reason theres 2 lines on the car but both push gas when I turn the key on and one is coming from the mechanical pump so idk whats up with that. Anyone wanna explain that one?

 

the larger line is the supply and the smaller is the return. Cap off the return with a hose and a bolt or something and run the supply to your mechanical pump. Make sure you have the right orientation of lines on your mechanical pump

 

i just purchased a 92 firebird and dropped a 350 into it, im gonna go the in tank fuel pump with a regulator to the carb, how do you go around the relay for the fuel pump without having the ecm at all? (i read somewhere that without the ecm, the fuel pump will not power at all)

 

I believe all the ecm does is power the relay when it needs it on. You just need to either run a rocker switch or a ignition hot wire to the same place on the relay as the ecm's wire.

 

The ECM grounds the fuel pump relay to turn the fuel pump on. So, if you do a switch, you need to ground the magnet circuit, not provide power to it.

 

And why I blew like 20 fuses in the front fender when trying to have a back up switch for my FP.

Took some trial n error to get it figured out.

 

The ECM is not needed to run the fuel pump - it's only needed to prime it. The Oil Pressure Sending Unit runs the pump in a constant state as long as it senses oil pressure. Yank the ECM out - the pump will function fine as soon as the OPSU picks up on the oil pressure created when you crank the car. Before that occurs, you have plenty of fuel in the carb bowls to start the car.

I switched to carb on my 1992 - and it runs just fine without the ECM - I added nothing and wired in nothing. The only issue is if I don't start the car for like a month - then the fuel in the bowls evaporates and it takes a few cranks to get the pressure built up for the OPSU to run the pump and start the car.

 

How much of a restriction is the in tank pump while doing this though?

 

I have a 86 camaro that had a 4.3 v6 tune port injection system now it has a 350 with 4 Barrel carb and it will run for a few mins then dies it has Manual pump on the side of 350 and intank pump too could this be my Problem

 

it takes for ever to crank back up like carb was out of gas

 

Nevermind problem Solved ran hose to return line and left pump in tank