Fuel pressure dropping while driving and under acceleration to zero at idle runs 4 lb electric Blue

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Demonx2 said:
These other fellas are telling you ideas that take some work but should absolutely work/solve the concern.

For me personally, before I got to the point of doing all that, I'd try your idea and then a simple relocate to behind the axle if that didn't help. That pump can lift fuel a bit - the question is how much under hot temps and when your demand is at its max. I'd make the easy changes and test it. But that's just my opinion.
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Just an update. I shorten the supply line about 9 in so now it comes straight out of the sending unit down to the fuel pump. The only pull it has is up the sending unit from the bottom of the tank. It made some difference but still drops when you get above 2000 RPMs. My next thing I'm going to try is to put a valve on the return and see if by shutting it down I can keep the pressure up. If not, I'm going to put a sump in the bottom of the tank and feed the fuel pump straight from the sump.
 
Ok, help me out here. Refresh my memory. This is a Holley pump with a return line correct???

I don’t know why (other than I’m getting older) but it occurred to me that when I started bypassing fuel with those pumps I always either went into the pump and blocked off the internal bypass with a piece of tubing so it could never open. Then I used a number 8 high speed bypass from Kinsler or someone set at 20 pounds to keep the pump from deadheading and blowing itself apart.

Or, they made a 15 pound bypass spring (IIRC) and I used that with a washer or two under the spring to get the line pressure to 20 psi.

If you have a return line and the buyer pass opens it may be staying open and dropping your fuel pressure.
 
Rat Bastid said:
Ok, help me out here. Refresh my memory. This is a Holley pump with a return line correct???

I don’t know why (other than I’m getting older) but it occurred to me that when I started bypassing fuel with those pumps I always either went into the pump and blocked off the internal bypass with a piece of tubing so it could never open. Then I used a number 8 high speed bypass from Kinsler or someone set at 20 pounds to keep the pump from deadheading and blowing itself apart.

Or, they made a 15 pound bypass spring (IIRC) and I used that with a washer or two under the spring to get the line pressure to 20 psi.

If you have a return line and the buyer pass opens it may be staying open and dropping your fuel pressure.
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Yes it's a Holley blue pump with a fuel lab regulator with a return.
 
I don't know...it's the way I bought it. I can ck into it. It made a difference making the line shorter and direct to the pump...it takes longer for the pressure to fall then it did before
 
flathead31coupe said:
Any suggestions?
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Get a gauge on the line after the pump and see how much pressure you have before the regulator.

If it’s not 15 psi you need to get it there and 20 psi won’t hurt a bit.

Holley used to make a 15 psi spring for those pumps but I’m not sure they still do.
 
The blue pump is 9 psi bypass if I remember right. The black pump is 14psi
 
Lol I'm still needing answers to post 112. But I thought I would give another update since I took the extra 9. In out of the supply line from the sending unit to the pump. I thought it was better until I went for a drive. Just driving normal pressure goes to zero while I'm driving. So it seems by taking the extra hose which made a loop along the frame at the top and back down removed some restriction which made the pump free flowing more. I'm not sure what's going on lol
 
TT5.9mag said:
The blue pump is 9 psi bypass if I remember right. The black pump is 14psi
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You are most likely correct because I haven’t used a Holley pump since 1986.

I do know they made a higher pressure spring for the blue pump than what came in it.
 
flathead31coupe said:
Lol sry iam kinda lost...why am I checking pressure before the pump, and checking what spring is in the pump...
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Because the fuel is going somewhere other than the carb. That’s why the pressure is dropping.

I mean it could be that the bypass valve in the pump is stuck half open or some of the vanes (or whatever they call them) are stuck halfway in their slots.

If your pressure is dropping the fuel is either A) going somewhere it shouldn’t be or B) the pump has a mechanical issue that keeps it from producing enough fuel to make any pressure.

That’s why I said check the fuel pressure in the line going to the regulator. It needs to be 15-20 psi. If it’s not, you need to figure out why.
 
Rat Bastid said:
Because the fuel is going somewhere other than the carb. That’s why the pressure is dropping.

I mean it could be that the bypass valve in the pump is stuck half open or some of the vanes (or whatever they call them) are stuck halfway in their slots.

If your pressure is dropping the fuel is either A) going somewhere it shouldn’t be or B) the pump has a mechanical issue that keeps it from producing enough fuel to make any pressure.

That’s why I said check the fuel pressure in the line going to the regulator. It needs to be 15-20 psi. If it’s not, you need to figure out why.
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I will check that fuel pressure as you suggested and see what it is. I was just told today by an old guy that the reason you don't have fuel pressure is cuz it's free flowing. It's flowing around and around and around with the return line. I have a 3/8 supply and a 3/8 return. So when I took the big hump out of the fuel line which was acting like a restrictor now there's nothing to slow the fuel pressure down other than the float bowls but it must be going past that and going right back into the tank
 
flathead31coupe said:
I will check that fuel pressure as you suggested and see what it is. I was just told today by an old guy that the reason you don't have fuel pressure is cuz it's free flowing. It's flowing around and around and around with the return line. I have a 3/8 supply and a 3/8 return. So when I took the big hump out of the fuel line which was acting like a restrictor now there's nothing to slow the fuel pressure down other than the float bowls but it must be going past that and going right back into the tank
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What do the instructions say for the regulator you are using?

Some of these regulators were designed so the return line was the restriction. If you sized the return line bigger than what was called for then you wouldn’t have any fuel pressure.

That’s what you need to figure out.
 
Rat Bastid said:
What do the instructions say for the regulator you are using?

Some of these regulators were designed so the return line was the restriction. If you sized the return line bigger than what was called for then you wouldn’t have any fuel pressure.

That’s what you need to figure out.
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I'll take a look. Thanks
 
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flathead31coupe said:
So do I just take the line loose at the regulator from the pump and put a gauge right there on the line coming from the pump?
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What do you have for a pressure gauge? You just need to tap into the line to the regulator and see how much pressure you have with the engine running.
 
Rat Bastid said:
What do you have for a pressure gauge? You just need to tap into the line to the regulator and see how much pressure you have with the engine running.
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i put a gauge on the side of the regulator i took a plug out
Rat Bastid said:
What do you have for a pressure gauge? You just need to tap into the line to the regulator and see how much pressure you have with the engine running.
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I took the plug out of the regulator on the side and put a gauge there. It showed 5 lb. The same as the other two gauges I already have on the car
 
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