Can't get Fuel pressure above 5.5 psi
 

Im running a holley pump part number 12-801-1 with Mallory 4309 fuel pressure regulator. It doesnt matter if i screw the hex head bolt in or out, the fuel pressure stays the same at around 5 psi while not running, but with the key on, and at about 5.5psi running.

Any suggestions?

First have you checked your gauge against a known accurate one?? Every fuel gauge I've seen is off one way or another. Second why are you using a regulator on that fuel pump?? Max pressure is 7 psi. By pass the regulator and see what happens. Justy throwing out a few ideas.

Only reason the running PSI would be higher than off or static PSI is supply voltage increase. What voltage is @ the pump key on and key on running?

Second thought would be to check flow or volume output. What id the floe in say 1 min.?

Thanks for the advice and ideas.

I'm just using what was recommended and it was recommended that i use this pressure regulator with a return line to the tank. This is my first 427FE build and i simply copied other 427FE Kirkham builds.

Im using a gauge that is connected directly to one of the pressure regulator ports. Im using a fuel level gauge, so i do not have a pressure gauge installed in the dash.

The voltage at the pump is 12.7

What size is the fuel line? How far is it from the pump? Where is the guage in the line of items? Is the guage functioning properly? Is the regulator functioning properly? I know these are all dumb questions, s$%t happens.... I had a bad guage that was stuck on 2psi. If I tapped on it, it would move to the correct running pressure. S$%t happens!!!

Ditch the regulator. Not needed with a 7psi pump. Return line not needed either.

Your Holley pump has an internal pressure regulator that limits output pressure by diverting fuel coming out of the pump back to the input side. The valve that diverts the fuel is controlled by a spring that is supposed to move at about 7 PSI. If the spring is not just right, it could open at 5 PSI and that is all the pressure you would see.

Fuel circulating through the Holley pump's internal regulator is subject to heating from the pump and can lead to vapor lock. The usual solution is to install an external pressure regulator that controls pressure to the carb by diverting excess fuel back to the fuel tank. Of course the external pressure regulator can only do its job if the fuel leaving the pump is at a higher pressure than that set on the external regulator. If, as in your case, the pump is putting out less pressure than is set on the external regulator, the external regulator will never sense enough pressure to divert fuel back to the tank. Thus the external regulator is useless in this case.

I learned this by suffering vapor lock on my Holley red fuel pump. I solved the problem by adding the external regulator and return line, AND by replacing the stock spring in my pump with a much stronger one. The stronger spring effectively prevents the internal pressure regulator from working, allowing the external regulator to do its job. I suggest you either do the same or replace the Holley red pump with an unregulated pump.

If you spell it FUEL, instead of PEUL, i'm sure it will rise to the proper pressure. lol

I've had a different experience with my Red pump. Never a vapor lock problem and it feeds a Carter 7 psi mechanical and dead-heads at the dual quad log. No regulator.
Since 1991.

Did you see DV's post on about the same issue.

See post #16 here: http://www.clubcobra.com/forums/clas...-one-me-2.html

Don't know if it will help or not.

Ran out of gas a little while ago while attempting to tune the car and it dropped to 2 then to 0 PSI Got fuel, put fuel in car, turned pump on, took screw out of pressure regulator and it dropped to zero. Reinstalled screw and still it only went to 4.5psi in run and around 5psi running. Point of this babble, i think the pressure gauge is working correctly and so is the regulator.

I will take the pump apart tomorrow and try the above fix in the link. Thanks for the help, suggestions, and link.

I didn't have trouble with mine either when cruising around town or on cooler days at the track. But on a hot day at the track when it was using a lot of fuel, mine vapor locked coming back into the pits.

Just speculating Tommy but how do you know it was the pump? Possibly the line near the carb or the carb itself heat soaked as you were traveling slower than track laps??
My experience is that the electric pumps cooler fuel than the mechanical during hot conditions and I always have a good feed.

My understanding is this. If fuel in the line or carb float bowl vaporizes, that bubble will be displaced by fuel from a working pump. For example, if fuel in the float bowl vaporizes, the float will fall, the valve will open and the pump will replace the vaporized fuel. It might cause a momentary hiccup, but not a prolonged loss of fuel. When my car stopped in the pits for lack of fuel, I solved the problem by putting ice on the fuel pump for ten minutes or so. I'll add that the problem has not reoccurred since I modified the pump and added the external regulator.

I agree with displacement of the fuel vapor by the pump and understand that you isolated it (to the pump as cause) with the ice-down. Good thinking and thanks for the explanation.
Just a little surprised you don't run a mechanical as well on a track car (as back-up). I've never been 'fuel-stranded'.

The insight in this thread is why i love a forum like this that has a community of people that house a wealth of knowledge and education beyond most all other forum populations. Thanks for contributing!! I always enjoy reading posts like the ones above and learning more.

Update: My pump is different from the one in the link posted. I took the pump apart just to get an understanding of how things work, but there is not a slotted washer and seal. I called holley and they said the only thing that would cause a lack in pressure from the pump would be if the bypass valve was stuck, but it appears to be fine. So, next step is to disconnect the return line, block the port at the regulator, and check the pressure with it set up in that orientation. However, while i have this all apart and the tank drained, i need to fix the fuel level gauge first. I swear my to do list is growing instead of shrinking.

Sounds like you are on the right track in checking every thing out. KEEP THE RETURN FUEL LINE! Depennding on the fuel you are using (oxygentaed etc) it will save you a lot of headaches with vapor lock. In Arizona vapor lock can be a big issue due to the heat and the fuel mixes. In tests, some of the oxygentaed fuel we get in TUcson and Phoenix begins to "boil" at 160 degrees. I have installed return lines on 6 Cobras including a Kirkham which has two fuel pumps, an electric and a mechanical. Solved the dreaded vapor lock.

Ok, the car is pretty much complete and i am now back to tackling the fuel and ignition problems.

I replaced the summit fuel pressure gauge with an aeromotive unit and i put it inline before the carburetor. Battery is fully charged and i am only getting 6PSI with the fuel pressure regulator completely closed off.

Time to send the pump back???

http://i932.photobucket.com/albums/a...a/DSC_0448.jpg

I went from the 2 7 psi pumps to 2 15 psi 100 gal/hr, 5/8" fuel line BG diaphram adjustable fuel log adjusted for about 6 psi inches away from dual carb single inlet and return line to tank. I think it is noiser. I think I loose fuel to avaporation in tank due to airation. And lastly BG went out of busniess and if anything ever happens to regulator, I do not know what I'll do.
My fuel tank has a dropped forward facing sump just in front of rear diff , Fuel flows first from two seperate pickups at differenet heigths in tank sump, pre cleaner filters, fuel pumps, inline check valves, billet "Y", BG 5000 filter on firewall, then to front of fuel log, past carb single inlets. The adjustable fuel pressure regulater is at rear of fuel log and then fuel line returning to right front of fuel tank. I tried to make an intank difuser for returning fuel line so fuel doesn't spray upward to hit inside top of fuel tank, like a fountain. Everything near engine is wrapped in refelective heat sheilding. Hard tubing and SS flex braided fuel hoses where needed. Fuel vapor lock has not been a problem since.