Hello Everyone, I normally just to searches to answer questions and rarely put out a new topic but this has me a bit confused. My question is about the fuel system on my 2.8L V6 with a 390 Holley carb that I have put together in my 88 GT project car. Now my understanding is that you run a 4cylinder Fiero fuel pump with the feed line going to the filter and than up to the fuel pressure reglator and than the fuel pressure gauge and than the carb. The regulator I have is also a Holley and has one in and two outs. My thinking was that the 2nd out would go to the return line and back to the tank.

Do I have to have a return line? I have heard people say both. And if you do than how does the regulator determine which Out is for the carb and which is the return line. There is something that I am missing or not completely understanding so please reply.

Oh, and please don't let this start a thing about carbs vs fuel injection

It depends on which model regulator you have. If it is a 1 in and 2 out, You block one side and run the other to the carb. Set it for about 6psi while the engine is running. If it is a 1 in with an output and a return, The return line goes back to the tank. If you runthe 2nd output of the basic regulator, You won't have proper line pressure which could cause some fuel starvation under WOT conditions.

Pressure creep is when you have a very high pressure like the 42 psi of the V-6 fuel pump and you try to regulate it down to 6psi with a regulator without a return. The 9-12 psi of the 4-cyl fuel pump won't cause pressure creep unless it is a very cheap regulator.

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And you have to have a return line. The constant fuel flow through the pump is what cools it, otherwise it will suffer a quick death.

JazzMan

I use the second out (it's there for the guys running dual quads BTW) as a return line to the tank by placing a small needle valve as a restriction in the return line. you can buy a small valve at a hydraulic supply house. all you need is a very small amount of fuel to pass the valve and return to the tank to keep things operating smoothly.

In my setup I use the original V-6 fuelpump and have created a restricted return BEFORE my Holley fuel pressure regulator.
I plugged one OUT and used the other to feed my carb.
Most common Holley pressure regulators have two OUT's that have an open connection.
Hope this helps.

Here is the Mallory bypass unit I picked up at Jegs. I actually hooked up the fuel pressure guage wrong in the picture but I'll explain.

The bottom outlet is the return line. There are 4 side outlets of which 2 are plugged.

The fuel pressure guage is actually mounted on the line going to the carburetor. (top left on mine) The intake is top right.

The nut and thread at the top adjusts your bottom outlet apperture which directly controls your psi.

Essentially, when you back the bolt out, the fuel pressure drop, and when you screw it in, the fuel pressure goes up.

One thing though, which can drive you crazy. As the oil-filled fuel pressure guage heats up, its value changes and it reduces the indicated pressure, even though the pressure hasn't changed at all. You want this regulator and fuel pressure guage in a relatively cool place or else get a standard fuel pressure guage, not oil filled.

Good luck with your carb.

Arn

[This message has been edited by Arns85GT (edited 02-14-2005).]

quote Originally posted by JazzMan: And you have to have a return line. The constant fuel flow through the pump is what cools it, otherwise it will suffer a quick death. JazzMan

Maybe with the V-6 pump, But I haven't had any problems with the AC Delco 4-cyl pump.
I have run it the same way with the carb'd 3.4L for over a year and it's the same set-up with the V-8 now.

Thanks, and as usual you're correct Oreif.

I used the stock v6 fuel pump because mine was low hours and it was a waste to chuck it. The bypass regulator prevents "creep" and will step the 40 psi down nicely.

The 4 cylinder pump just needs the regular blue Holley regulator.

Arn