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

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flathead31coupe said:
i put a gauge on the side of the regulator i took a plug out

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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Ok, so you are saying you have 5 psi in the line from the pump to the regulator? If that’s correct you need to figure out why that is. That system will not work with that pressure to the regulator.

So the bypass in the pump may be stuck half open or you have issues with the vanes in the pump.

You need to sort out the low pressure in the feed line before you do anything else.
 
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 it showed the same as the other two aleady o
Rat Bastid said:
Yeah, you need to check the pressure before the regulator.
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On the last pic it shows the regulator. The Holly regulator underneath is all gutted completely out. It's just a t to supply both of my carburetors on the front hose going to front carburetor. There's a gauge then on the back hose going to the other carburetor is a gauge going to the one mounted on a plate behind the air cleaner and I took out the brass plug and put a gauge there and they all read the same. But I will get a few fittings for the incoming side of the regulator and put a gauge there
 
flathead31coupe said:
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Looking at the bottom picture, take that fuel pressure gauge fitting off the feed line to the rear carb and put it in the line coming in to the regulator. Which looks like it’s the line right above it.

That will tell you how much pressure you have getting to the regulator.


EDIT: I would eventually move that little gauge over to the pressure side of the regulator so any time you want you can see what the pressure is getting to the regulator.

You don’t need to monitor the pressure to each carb inlet. They will both be the same.
 
Rat Bastid said:
Looking at the bottom picture, take that fuel pressure gauge fitting off the feed line to the rear carb and put it in the line coming in to the regulator. Which looks like it’s the line right above it.

That will tell you how much pressure you have getting to the regulator.


EDIT: I would eventually move that little gauge over to the pressure side of the regulator so any time you want you can see what the pressure is getting to the regulator.

You don’t need to monitor the pressure to each carb inlet. They will both be the same.
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I will have to get a fitting tomorrow for the gauge. The fuel lab has some kind of fitting that uses o-rings or I would just swap like you were talking. But I will take the gauge off. I agree you only need one going to the carb since both will read the same
 
flathead31coupe said:
4 1/2 psi at the incoming side of the regulator. And 5 1/2 psi coming out. How's it that even possible
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Ok, your are correct. That makes NO sense. Hmmm.

I would fix the pressure to the regulator first. I would get the pump off the car and look very close at that internal bypass valve and make sure it’s not boogered up and stuck half open or something. And if it’s working, get the high pressure spring for it. I used to have a test fixture to test little springs like that for when I ran and was tuning mechanical fuel injection all the time. I think I sold it though.

You need to get that pressure up to to at least 15 pounds. 20 would be better.

Once you get that corrected you can tackle the pressure after the regulator.

4 pounds of line pressure to the regulator is way, way too low. That has to go up first.


That’s crazy…
 
Rat Bastid said:
Ok, your are correct. That makes NO sense. Hmmm.

I would fix the pressure to the regulator first. I would get the pump off the car and look very close at that internal bypass valve and make sure it’s not boogered up and stuck half open or something. And if it’s working, get the high pressure spring for it. I used to have a test fixture to test little springs like that for when I ran and was tuning mechanical fuel injection all the time. I think I sold it though.

You need to get that pressure up to to at least 15 pounds. 20 would be better.

Once you get that corrected you can tackle the pressure after the regulator.

4 pounds of line pressure to the regulator is way, way too low. That has to go up first.


That’s crazy…
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Ok thanks
 
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I had a chance to look at the fuel pump tonight. I took the bottom plate off and the spring out and the little plunger. It looks in perfect condition. No sticking at all in the picture. One of the little vains fell out I have it.. now I am not sure where to go from here. Is it hooked up backwards? Can anybody tell by looking at the bottom? I haven't crawled underneath to verify in and out. I'm pretty sure it's right, but at this point who knows lol in the picture that incoming fuel is at the top and going to the carburetors at the bottom.
 
I talked to fuel lab today, They said the chances of that regulator being bad or slim to none. They said that at the regulator inlet where the fuel gauge is should read the pressure of the pump. I have a spring coming that will raise the pressure to 12 to 19 lb. They said if that don't do it then you need to replace the fuel pump. I've been told by several people if you buy one. Holly fuel pump buy two lol
 
Okay, here's a recap. First Holly blue fuel pump with stock plumbing configuration could be regulated to 5 and 1/2 PSI. But as the RPMs went up it would drop down too close to zero but would come back up when you stop at a stoplight. So installed a new Holly fuel pump. Shortened up the line going into the pump from the sending unit. Made a direct path for the fuel. Fired it up. It would go up to 5 and 1/2 and then dropped to zero. When you take it for a drive it stays at zero. So I took the pump apart. Everything looked brand new bypass spring and piston look new move freely. So I got a moroso. Holly fuel pump spring to make the fuel pressure 19 PSI install the spring fired it up. I can only get six PSI before the regulator from the supply line from the pump. So it's either the pump or something's wrong with the regulator. I talked to fuel lab. They said that regulator is idiot-proof. It's most likely not. It. Must be the pump. Ideas or thoughts?
 
flathead31coupe said:
Anyone have thoughts or ideas? Should I take this fuel lab regulator part just to be sure or just get another pump? It can't be this hard lol
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Dead head the pump and see what it makes for pressure. The pump may be junk. I will say I’m not a fan of regulators that send the fuel in the side and return it out of the bottom.

But I’m not throwing the regulator under the bus yet.
 
Rat Bastid said:
Dead head the pump and see what it makes for pressure. The pump may be junk. I will say I’m not a fan of regulators that send the fuel in the side and return it out of the bottom.

But I’m not throwing the regulator under the bus yet.
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So just take the return out of the loop and run it without a return. Is that correct
 
flathead31coupe said:
So just take the return out of the loop and run it without a return. Is that correct
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Yes. If it still doesn’t have any pressure it’s most likely the pump. I looked at that regulator again and I’m not sure there is any way it could drop the fuel pressure like that. The first suspect is the pump IMO.
 
Rat Bastid said:
Yes. If it still doesn’t have any pressure it’s most likely the pump. I looked at that regulator again and I’m not sure there is any way it could drop the fuel pressure like that. The first suspect is the pump IMO.
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Just for kicks, I took the regulator apart. The four bolts left it up. There is a spring and a rubber diaphragm with a metal tapered piece underneath and then I can see the fitting for the return. So the diaphragm is all that's in there in a spring so I'm pretty sure that's not the issue. I will let you know when I get off work and try to deadhead. Thanks!
 
So I took the return line off and plug the regulator where the return line goes. I turned on the fuel pump and it takes about 30 seconds or longer and barely makes it to 11psi with the 19 PSI spring in the pump. I guess that tells the story.
 
flathead31coupe said:
So I took the return line off and plug the regulator where the return line goes. I turned on the fuel pump and it takes about 30 seconds or longer and barely makes it to 11psi with the 19 PSI spring in the pump. I guess that tells the story.
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That appears to be your problem.
 
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