Fuel Pressure drop...but why?

[theCRANKwalker]

here is my setup... walbro 255 high pressure, -8 feed, -8 filter, -8inlet on stock rail, 680ball style injectors, -10outlet to aeromotive FPR, stock return line

-i can set base idle pressure to 40psi, i can go as low as maybe 36-37 psi but no lower lets say i wanted to
-my major problem is that under boost my FP drops from 40psi to 30psi
-also at idle, when i hit the gas, the FP drops a few lbs. instead of rising
-i set base idle pressure with the vacume line off, then apply the vacume line
-i've tested the FPR at idle giving it 20psi from a compressor and FP did rise 20psi, so i know the FPR is not broken
-i've spoken to a few people, some think the pump is not big enough but i can't see how because so many people use this pump without a problem

i spoke to an aeromtive tech and we both think it is the return line maybe not being big enough, backing up the line and not letting the regulator do it's job correctly, i already ordered -6 line to replace the stock line and my fingers are crossed that this will rfix the problem, i am running this by you guys because maybe you've run into a similar problem and fixed it, i could use any advice, i can't go to the dyno until this problem is fixed

thanks,
jerry

 

[kpt4321]

If the return line was redtrictive, then you would see a fuel pressure that was higher than it was supposed to be, not lower.


....Kyle T.
93 TSi AWD "TURBO4'
14b - 12.8 @ 108

 

[theCRANKwalker]

Originally posted by kpt4321
If the return line was redtrictive, then you would see a fuel pressure that was higher than it was supposed to be, not lower.

i'd love to totally agree with you on that and it was a thought of mine, but after speaking with aeromotive, there is a light possiblity that the FP is getting backed up and not letting the FPR work properly thus showing a bad reading

it's very frustrating and i'm doing one thing at a time to fix it, i will replace the return line as that seems to be the cheapest move and if that doesn't fix it, then i'll move onto whatever the next fix might be

a friend of mine has an uninstalled reulgator we're gonna throw on there too to make sure there is nothing wrong with mine

 

[NDgsx]

It is a return line line problem, but it's not the hose diameter.
It's the siphon system in the fuel pump assembly. Look at the diagrams in the factory manual and then take the pump assembly out. If you bypass the siphon tube your restriction will be gone, but you'll only have a half tank of useable gas. 2G awd tanks have a hump in the middle and are basically like two seperate tanks.
I don't have a good solution for you, I've never had to deal with it personally (owning a 1G).

 

[theCRANKwalker]

why would this problem occur all of a sudden? is the siphon tube clogged maybe?