turbotuner20v

So I've had this issue since early 2013 when I first took the fuel system apart as part of my build. I installed a brand new OEM Z06 fuel assembly back then and after a few hundred miles it dropped pressure to ~22-30psi. To work around this I installed a manual toggle switch to bridge the Hobbs switch and ran the car on the external magnafuel pump. I just replaced the Z06 pump with a walbro 450 and again it is dropping to ~22-30psi (but on cold starts seems to make full pressure ~46psi). The siphon system still works fine, it just isn't making full pressure to drive on it alone out of boost and actually use the Hobbs.

Stock pump feeds the ‘Y’ below 3psi, then above 3psi, both pumps are running. The fuel return uses the stock feed line:



Maybe it's some loose oring or connection in the siphon system bleeding pressure? I literally have no idea what to do other than replace everything in the tanks (pump assembly, siphon, plastic tubes)

gotjuice?

Where is your check valve that would prevent the factory pump from feeding the fuel back thru the Magnafuel pump into the tank?

gotjuice?

You can see my check valve, small black, right at the back of the fuel tank. My Magna fuel setup was similar to yours. I believe there is another one in the rocker panel after the Magna fuel pump before the Y.

gotjuice?

This is probable a better picture.

turbotuner20v

Magnafuel states that fuel can not back flow their pump. I did add a check valve in the line between the stock pump and the Y block (not pictured in this old pic) so the in tank pump assembly wouldn't get back flowed by the magnafuel pressure (unlikely, but I figured why not). I guess I could add another 'why not' check valve between the bulkhead feed fitting and magnafuel to ensure fuel isn't bleeding back into the tank

gotjuice?

Edit, I think I see the valve, Maybe something stuck and keeping it open or just not working correctly. I would check that first.

turbotuner20v

Adding a check valve between my Y block and the magnafuel post pump filter in that vertical hose would be very easy and could confirm the pressure isn't being lost by back flowing the magnafuel... I'll try that first.

I assume Russell -08an check valves flow well enough it won't limit my pump output?

gotjuice?

Disconnect at the Magna fuel pump and run on just the factory pump. See if you are getting any fuel headed back to the tank.

whatcop?

Either backflow through the magna pump since turning it on makes the problem disappear or a faulty check valve that isn't opening post stock pump.

gotjuice?

I used the aeromotive one that came with the stealth set up. It was an -08.

whatcop?

What I was thinking as I was posting. Didn't see this post till after I posted.

whatcop?

You could unplug the magna and run the car and then see if the magna feels warm. That will tell you that it is backflowing and the pump was turning. Just don't know if it will get warm enough.

turbotuner20v

I could get a pinch clamp for the bulkhead to pre pump filter hose and disconnect that line and then run a drain line from the pump pickup down into a bucket. Then idle the car and see if pressure stays up and no fuel comes out

gotjuice?

Then there would be no need to disconnect the line. You can see that with just blocking the line. The fuel pressure with increase.

whatcop?

Excellent idea

turbotuner20v

Touché... Sometimes pressure starts normal and dies off later though, so I'd like to see fuel pouring out

turbotuner20v

Started the car using only the in tank pump and it idled at 47psi for about 30 seconds to a minute, then dropped to 30psi. I clamped the magnafuel feed line that runs to the tank bulkhead fitting and it didn't change the pressure, just stuck at 30psi....

turbotuner20v

Made a test pull to ensure the new build pulls cleanly for the dyno and I'm ~9.2:1 afr around the upper rpms, so at least it seems like fuel supply won't be an issue

whatcop?

Do the same test and pull the check valve. It could be something crazy like the sensor for rail pressure is damaged.

turbotuner20v

The pressure sensor on the regulator that runs the gauge is reading accurate, when I turn the magnafuel on the pressure jumps back up