Heres the fuel system.

NON LIQUID FILLED GUAGE

Magnafuel quick star 300 pump
10AN supply to filter
Allstar filter threaded directly into pump
Pump
8AN bypass back to cell
8AN supply to regulator deadheaded per magnafuels instructions
Regulator connected directly to fuel rail
Fuel pressure guage directly into regulator
8AN vent

Presures. Bypass pressure is set at 18 psi. Regulator pressure is set at 7 PSI.

Heres the problem. Fuel pressure is perfectly stable at idle. Its stable during normal driving. Under full throttle acceleration is a different story.

The fuel pressure guage starts vibrating like crazy around the top of first gear and along with the vibrating the pressure proceeds to drop in second and third until it gets down around 3 psi by the end of the run. It seems to be getting worse. Now the car is nosing over around 6250-6500. When you let up on the throttle the pressure slowly rises and stablizies as you reach the end of the shut down.

This is the same fuel system I ran with my 775 hp big block. This is the first time ive ever had this issue.

I replaced the fuel cell vent with another new hose.
I cleaned the regulator, looked good inside
I had the pump rebuilt by magnafuel
I cleaned the fuel filter
There dosent seem to be any cavitating noises from the pump

Im kinda lost on this problem. Any help would be appreciatied. But fwiw, I ran the same time shifting at 6500 as I did at 7000 rpm. Glass half full, it means theres more in the car, lol. Thanks, Eric L

 

I would raise the bypass pressure. I saw the same problem on my dyno guys dyno fuel system

 

Wow. Really? I would have thought that 18 psi of bypass pressure would have been enough. I'll bump it up to around 22 psi. Thanks for the input. Eric L

 

I tried 23 psi of bypass pressure, same results. I think if I have time tomorrow ill drain the cell and reseal the bulkhead fitting, check the filter, and inspect the short piece of 10 AN from the cell to the filter. Eric L

 

Do you think it could be sucking air at the filter ?
Thinking it could be the seal is made for pressure Vs. vacuum ?

My filter is after my Aeromotive pump...same way it came out of a buddies 9.teens BBC car. Deadheaded, -8 line, Holley regulator, -8 to carb.

 

Foam filled cell? Is the cell full of fuel?

 

http://m.summitracing.com/parts/aaf-all40218

That is my filter. This is the same way I ran it with my big block. It's an oring seal.

 

Foam was removed for use with pump gas, and the cell is always kept at least half full. Eric L

 

I would close the bypass completely, and try it. To rule it out.
Edit: I'm assuming your fuel filter checks out. Thats obviously the first thing to check

 

Just get an 8an cap and block it off at the pump? What problem are you thinking the bypass could be causing?

 

And fwiw, I have my bypass plumbed into the top of the fuelcell. Eric L

 

The only other thing that I can think of other than a failing pump is electrical connections. My buddy's car just recently started doing that and he found a poor ground. He fixed that and it fixed the problem.

Oh, and one more thing. I have seen feed hoses from the cell to the pump get old and start to collapse inside under suction.

 

The electrical is in tip top shape, but I'll go over the connections again and make sure all is well.

The short supply hose IS old, and that was one of my thoughts as well. Thanks, Eric L

 

Guess who just figured out that he installed his fuel filter cartridge backwards after cleaning and reinstalling it?




LOL at mmmself

Better track times coming soon, lol.

 

Good stuff. Gotta love zero $ fixes, even if its your own F up

 

I just went thru this sort of issue yesterday. Turns out my surge tank was not staying full and my fuel pump was starving and sucking air. Had a plugged fuel filter from the feed to the surge tank. Figured that out AFTER I bought a new Bosch 044 pump.

Check fuel filters guys! Lol

 

The thing I can't figure out is that I never heard it cavitate, not once. I still need to test drive it today before I go to work, but I think we got it. Eric L

 

Test Drive

It's deffinately much better. It doesn't seem to nose over on top end any more. The guage still bounces, which I think is just from how it's mounted on the cowl.

During the run, by the middle of third gear the pressure is down around 3 or 4 psi.

I checked the supply hose and it seemed to be fine on the inside and wasn't collapsing.

Is a slight pressure drop normal? I don't remember it doing this with the last motor.

Maybe it's time to replace the diaphram in the regulator?

 

The pressure should stay dead solid. Can you post a picture of your fuel cell/fuel pump layout? And, regulator to carb layout?

 

mine did that when I had finally outgrown my pump, truck kept getting quicker and I never thought to upgrade my fuel system to handle the needs of the engine.