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

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flathead31coupe said:
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?
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That's the basic idea, yeah. Below and behind is much better than above and in front. If a sump added to a stock tank (welding on a NEW one is a better idea than your old one) gets you to a point where you can mount the pump behind it, that should work.
I think the problem with my sump-added stock tank was the factory shape was not conducive with the sump, feed to the sump wasn't great under acceleration.
Edit: I think TT5.9mags idea is an excellent one for you.
 
flathead31coupe said:
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?
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You will make it much easier for the pump to maintain pressure if you reduce any length/restriction on the suction side. As others have said, ideally the pump could be behind the tank and below it but not many would want the pump hanging low exposed to curbs/aprons/etc. So you mount it to try to reduce any uphills or bends or lengths wherever and however you can.

My avatar has a fuel cell sitting in the spare tire well and the rear exit of it travels to a large spin-on canister filter which then feeds the pump on the inside of the RH rail before the rear axle. So the pump still has to suck a bit but it's travel and length/restriction is minimized. Ideally you want "just enough" pump to cover the engine's appetite at 6 psi at WOT (for a carb) without having so much pump that at part throttle or idling the regulator is fighting to hold pressure down at 6 psi. This is where a return line would help...but there is no free lunch as circulating fuel only heats it up as it goes through the pump and then up to the engine bay and back. Simple physics. I suspect that Holley Blue pump is sufficient but only if it is not restricted on the inlet side. At least it's worth a chance to see!
 
Well I think I've decided to try to fix this myself with what I have. I have done some searches and there is a lot of different ideas on how to mount the pump down low enough to gravity feed from the factory sending unit. Does anyone have a good picture of one of the best ways to do it? I'm going to try to get out there in the morning and see what I can come up with. Just trying to get some pic ideas Thanks
 
flathead31coupe said:
Well I think I've decided to try to fix this myself with what I have. I have done some searches and there is a lot of different ideas on how to mount the pump down low enough to gravity feed from the factory sending unit. Does anyone have a good picture of one of the best ways to do it? I'm going to try to get out there in the morning and see what I can come up with. Just trying to get some pic ideas Thanks
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If nothing else, sump the tank. The vent MUST be the same diameter or bigger than pump feed line. Some will say it doesn’t matter but it does. Especially with a return line.

Get rid of the filter before the pump. If your tank isn’t full of **** there is zero reason to have a filter before the pump. That’s an issue as well.

Those pumps are picky about pulling fuel. Gravity fed is the best for those pumps but you can’t get that with your pump mounting. So reduce any restriction on the inlet side of the pump.

In fact, the sump should have two outlets in it. Use both of them and run the two lines into a “Y” and then a single line out to the pump.
 
Rat Bastid said:
If nothing else, sump the tank. The vent MUST be the same diameter or bigger than pump feed line. Some will say it doesn’t matter but it does. Especially with a return line.

Get rid of the filter before the pump. If your tank isn’t full of **** there is zero reason to have a filter before the pump. That’s an issue as well.

Those pumps are picky about pulling fuel. Gravity fed is the best for those pumps but you can’t get that with your pump mounting. So reduce any restriction on the inlet side of the pump.

In fact, the sump should have two outlets in it. Use both of them and run the two lines into a “Y” and then a single line out to the pump.
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I’ve said it twice here and multiple times on the forum in other places. We can preach it till we’re blue in the face, but people are going to do what they want to do. I wish I could hit the agree button multiple times on your post.
 
Thanks for the reply everyone. What I meant is that I am going to remount the pump in a way that is closer to the pickup outlet and go that route so it will be gravity fed. I was just looking for the best way to mount it with pics if somebody has already done it
 
That’s the thing, if you use the original pick up, the pump won’t be gravity fed. Look up what “head pressure” is and you’ll understand what we’re saying.
 
Specifically a pressure head from a column of liquid.
 
Sorry for My confusion So no matter what I do unless I put a sump where the gas is flowing down to the pump that I have and mount it closer it's not going to work no matter what configuration I do. I'm still going to have the same issue . it will be pulling through the pickup tube itself with my stock sending unit... And as stated many times before these pumps are better at pushing fuel then pulling fuel. Do they make a pump that can go in my current location that will pull fuel?
 
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flathead31coupe said:
Sorry for My confusion So no matter what I do unless I put a sump where the gas is flowing down to the pump that I have and mount it closer it's not going to work no matter what configuration I do. I'm still going to have the same issue . it will be pulling through the pickup tube itself with my stock sending unit... And as stated many times before these pumps are better at pushing fuel then pulling fuel. Do they make a pump that can go in my current location that will pull fuel?
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Yeah, but none of them are cheap. You are between and rock and a hard place.
 
Here are a few more photos. My question is will it make that big a difference if I mount the pump closer to the sending unit below the tank then it would to to take the supply line from the sending unit and go pretty much a straight shot to the pump that is currently mounted on the frame rail below the tank. So I'm initially taken out the large up sweep and back down making it more of a straight shot out of the sending unit to the pump.

PXL_20220915_192945571.jpg


PXL_20220915_192855539.jpg


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I can't tell for sure but it looks like the pump is mounted AHEAD of the axle. And you essentially replaced the fuel line from going up and over the axle to now coming straight from the tank, under the axle, and into the pump. If you've already plumbed it, I'd give it a try.
If it still has issues, make sure you minimize any restrictions ahead of the pump - be it fittings, filters, or whatever. If all that fails, then I'd move the pump behind the axle on the rail for a very short shot right into it out of the tank.
 
Demonx2 said:
I can't tell for sure but it looks like the pump is mounted AHEAD of the axle. And you essentially replaced the fuel line from going up and over the axle to now coming straight from the tank, under the axle, and into the pump. If you've already plumbed it, I'd give it a try.
If it still has issues, make sure you minimize any restrictions ahead of the pump - be it fittings, filters, or whatever. If all that fails, then I'd move the pump behind the axle on the rail for a very short shot right into it out of the tank.
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Sorry for the bad picture. The picture I posted shows the supply line coming out of the sending unit going up following the wheel well back down the frame and into the pump. That is how the setup is now. I was wondering if I shorten the distance and go straight from the pump over to the sending unit with a short piece of hose if it would make the same difference as moving the pump closer to the sending unit with a short line
 
Put a -8 fitting in the bottom of the tank and feed it from there. Mount the pump like the one in post 94. That's what I did, never had any issues.
 
flathead31coupe said:
Sorry for the bad picture. The picture I posted shows the supply line coming out of the sending unit going up following the wheel well back down the frame and into the pump. That is how the setup is now. I was wondering if I shorten the distance and go straight from the pump over to the sending unit with a short piece of hose if it would make the same difference as moving the pump closer to the sending unit with a short line
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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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