i sumped my stock gas tank and ran a external fuel pump with a pre filter and a inline filter with 8an lines to my fuel rail and im useing th stock return line back. im running dfi in my car without the factory ecm so my purge cannister is no longer used.
after i run the car for awhile my tank pressurizes to the point that it starts to drop fuel pressure. im useing the factory vent, and a vented gas cap but the only way i can get it to stop is to leave the cap loose so air can get by. when the tank is full gas sloshes out and the fumes are horrible! now i know alot of people have gone to bigger lines and pumps, so please help me out and tell me what i missed or am doing wrong! thanks in advance

 

What filter do you have before and after the pump? What are they made of? And why do you have both?

Also why did you not upgrade the return line?

 

ken,
the two filter setup is common, the factory pump has a pre filter inside the tank that attaches to the pump (called a sock usually) i used a russell competition (disc type) as my pre filter since my tank has a sump welded to the bottom and any crap in the gas will most certainly get sucked into the line since the pump is inline. then i have a russel pro filter to over kill clean the gas. its kinda big, almost a foot long. but for the price, its a good investment.
as far as the return, kinda a gamble that worked out? the point of the bigger line and pump is to put more fuel into the motor not pump it back to the tank. since im useing the accel pump (800hp), its not overkill for a 550hp stroker with a 200 shot. i get very stable fuel pressure(with the cap loose) and so far doesnt seem to hurt anything. but maybe this is causeing my tank trouble,dont know. maybe it is not pressurizing, it is vacuum, from more fuel leaveing the tank then coming back?

 

So you only have trouble with fuel pressure with the cap on?

Reason i asked about the filters, is because in my last SS i had a sumped tank with Aeromotive external pump. And had a paper element filter before the pump which is a big nono and caused cavitation and fuel pressure problems. The finer paper filter is suppose to be run after the pump whereas a metal medium filter is suppose to be run before the pump. So i thought to i'd bring it up just to make sure.

Here is a referance-
http://216.242.145.16/products/content_p.phtml?pk=10

 

Somehow, I think the initial thought - excessive tank pressure - isn't correct. In a "looped" fuel system, both ends of the system connect to the tank, so a pressure in the tank shouldn't hurt you at all, except as noted below.

Where you get into trouble is when you start to flash the fuel to vapor in the pump suction line. Several things can contribute, including:

-tank vacuum

-too small a suction line - I wouldn't run anythingless than a -10AN line on the pump suction line.

-plugging of pump pre-filter. Nothing wrong with having a filter before and after the pump.... a 40-45 micron metallic pre-filter protects the pump, a 10-12 micron line filter after the pump protects the injectors. The filters must be kept clean. A paper filter can require replacement after 20 hours.

-excessive fuel heat up from an oversized pump, a restrictive return line or running the lines too close to high heat components, like exhaust systems, etc. High temps are indicated by excessive vapor from the tank - e.g. "the fumes are horrible!"

 

I don't mean to butt in on your thread but I had a similar problem. Excessive tank pressure, big time fuel odor, etc. I was using the Aeromotive F-Body system so I was using an A1000 to suck (actually siphon) fuel out the top of the tank. It used a 3/8 suction tube and I had cavitation problems big time. I am using the stock feed line and return line. I have sinced sumped my tank using -10 lines to the pump and I am using the aeromotive pre-filter. Nothing else has been changed and the car seems to be working fine.

Does anyone see anything that might cause problems in the future?

 

thanks guys for your help!
im useing a 8an line from my tank to the prefilter and then to the pump, maybe this is my problem? the accel pump has a nipple on the suction end not a normal pipe thread a -8 hose goes right onto it any ideas on how to get this to work with the -10 line? other than getting a new pump?

any opinions on useing the stock return line still ? is it contributing to the problem?