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

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The blue pump is rated at 88gph at 9 psi. Max pressure is 14.
 
Okay here's an update. I took the old regulator apart. Got it out. Drilled it out. It's nothing in it but just a tee to feed both carburetors from the fuel lab regulator. I had access to a brand new fuel pump. I installed a new fuel pump. Tested it. Not as bad as the old pump but still the same thing as the RPMs go up the pressure drops. I'm now going to check into the tank being invented and any other suggestions anybody has. To give you an idea it comes out of a 3/8 sending unit. It goes up a little bit along the frame rail. It comes down to frame rail to where it turns straight into a filter. Then my fuel pump, then another filter and then all the way up to the fuel regulator. The return goes all the way back to the sending unit.
 
So I had a question. If I'm using a carbureted system it doesn't need a return line, correct. The only reason I added a return line is I thought it would help cool the fuel. If I was having a vaporizing issue. Will a return line fuel system setup work with carburation?
 
The carb realy doesn't care about the pressure as long as its enough to deliver the volume getting emptied from the bowl. Higher pressure only increases aeration, and too high of pressure can force the needle valve open - especially when idling and coasting. Steady pressure in the 3 to 5 psi range is best because it will provide the most consistant fuel level in the bowl.

A return line can help keep fuel cooler than if its sitting in the line over hot pavement or in a hot engine compartment.
It can also make it easier to control pressure, especially with lelectric pumps using a high pressures needed for FI.
Mechanical pumps increase volume and mass flow with rpm.

Vapor. When gasoline vaporizes the pressure goes up.

The description you have posted is that there is pressure at idle - which is the condition where the engine is consuming the least amount of fuel.
The fuel bowl inlet valves are closed or nearly closed.
The reason the pressure drops with increased throttle must relate to a lack of volumetric flow. The suggestions to figure out whether this is due to a restriction or a pump failure is the way to solve this.

Ideas to persue
1. Hysteric or someone mentioned electric connections. If the pump is connected to a circuit that is a long distance and/or sharing power from the alternator, then there could be a drop in voltage and therefore poorer pump perfromance.

2. Location of the pressure measurements is critical to figuring out what's going on. Measure the pressure closer to the pump outlet, then the regulator outlet.

3. Do a set of pressure vs volume experiments. Skim through this, and then go back and read through the posts there as needed to understand. See what cudafever did to prove it and then I think you can apply it to your situation.
Holley/Demon Carb stumble (posts 472 - 491) See in particular the sketches of Cudafever's system in post 485, and his tests (488-491) that show lower pressure allows more volume to the carb.
 
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Thanks for the reply. I will reread through that information. As I said in my last post I took the fuel pump out of the equation. I had a brand new fuel pump that I installed on Saturday with new electrical fittings and a brand new pump. And it done the same thing. It would keep pressure as long it was. It was idling as I give it gas above 1500 RPM. The more I give it gas the more the pressure would drop
 
Have you done a fuel VOLUME test yet? Don’t assume the new pump is any better than the previous one. If pressure drops as the rpm comes up you have a volume problem. It’s that simple. Restriction on the INLET side of the pump is the usual cause, as well as an undersized fuel pump.
 
Okay I will do the volume check soon as I can. It just seems weird. 3/8 line in 3/8 line out all the way through the sending unit all the way to the regulator. I thought for sure that that Holly would handle that
 
It will. But you haven’t proven there is no restriction on the inlet side. Or that the pump will produce the volume it’s supposed to. Where is the pump mounted? And how is it drawing fuel from the tank? Is it gravity fed?
 
The pump is mounted in the back on the frame right? Where the it's straightens out after the wheel well opening. It comes out of the 3/8 sending unit. It goes over and down follows the frame rail down until it just straightens out to the pump
 
flathead31coupe said:
The pump is mounted in the back on the frame right? Where the it's straightens out after the wheel well opening. It comes out of the 3/8 sending unit. It goes over and down follows the frame rail down until it just straightens out to the pump
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Sounds to me like you’re asking your pump to pick up fuel through a factory sending unit with a 3/8 pickup and sock in the stock location with the pump mounted 4 feet in front of the tank. Imo that is a very less than ideal situation for that particular pump.
 
Here are a few pics.
PXL_20220822_234838048.jpg
PXL_20220822_234805372.jpg
PXL_20220822_234823755.jpg
 
I'm guessing this is less than ideal. Is there any way of making this set up work or do I need a different style of pump or replumb the whole thing? Ideas very welcome
 
If this was my car, I would:
1. Check voltage and electrical connections to the pump for resistance. How does the ground look? I see a butt splice and those trap moisture and corrode. Hell I think they corrode before you crimp them.
2. Remove all suction side restrictions to the pump and retest pressure.
3. The full stock fuel system should work great up until it vapor locks, at which point you could add a restricted bleed back to the tank. Simple and it works.
4. That crimp bend in your exhaust over the axle looks like a restriction that might make your engine run hotter. Might just be the camera angle :)
 
The Holley rotor/vane series of pumps (red, blue, black) are not designed to have to pull fuel in any way shape or form. They are designed to push fuel. They need to be gravity fed and have some head pressure on the inlet side. Your setup is exactly why people install these pumps and then complain to Holley when they don’t last more than a few miles. I can’t tell you how to spend your money, but that pumps needs to fed from the bottom of the tank from a sump and in a perfect world mounted lower and behind the tank.
 
I have another quick question. If I use the same configuration where the pump is located now but add a sump to a new tank or my tank and replumb the hoses. Will that pump work in its current location?
 
flathead31coupe said:
I have another quick question. If I use the same configuration where the pump is located now but add a sump to a new tank or my tank and replumb the hoses. Will that pump work in its current location?
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I did that "add-a-sump to a stock tank" thing. Didn't work for me. I put in a bottom feed fuel cell, with the pump below and behind the cell. Problems all solved.
 
33IMP said:
I did that "add-a-sump to a stock tank" thing. Didn't work for me. I put in a bottom feed fuel cell, with the pump below and behind the cell. Problems all solved.
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you wouldn't happen to have a picture of that would you. I'm not sure what that looks like or I may have seen it not know what it's called lol
 
If I read your pics correctly, it seems the pump is ahead of the axle. That makes the feed line to it have to go up and over the axle.

Is it possible to put the pump behind the axle on the frame rail or somewhere else closer to the tank exit? That let's the pump not have to pull as much and should help it under higher-flowing conditions to be able to keep the supply flow/pressure up.
 
Demonx2 said:
If I read your pics correctly, it seems the pump is ahead of the axle. That makes the feed line to it have to go up and over the axle.

Is it possible to put the pump behind the axle on the frame rail or somewhere else closer to the tank exit? That let's the pump not have to pull as much and should help it under higher-flowing conditions to be able to keep the supply flow/pressure up.
Click to expand...
 
Anything's possible? If that's what I have to do I can make a bracket or whatever it takes to do so All I need to do is have the gas going into the pump so it doesn't have to suck gas over and into it, correct?
 
flathead31coupe said:
you wouldn't happen to have a picture of that would you. I'm not sure what that looks like or I may have seen it not know what it's called lol
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99% of fuel cells are bottom feed, just look at listing of fuel cells at jegs or summit.
Mine is in the trunk, with one feed line plugged (they usually seem to have two -8s, I change to one -10, out to a pump to the rear of the cell, (140gph trickflow in one car, 250gph Mallory gerotor in the other) then a fuel filter, then an aluminum 1/2 line to the dead head regulator. Stupid basic, but it works for me.
 
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