what are you using for a tank vent? so we're getting apples to apples, tell us about your fuel system too... i'm having a problem that may be related to how i've got my tank vented, but it could also be a regulator issue (too much pump, not enough regulator, etc.)

What's the prob you're having? My Holley Blue pump would shut down after a few mins of running.I had a relay put in,& the floats adjusted.It would run a few mins longer but shut off again. Then, I took it to a friend's shop. They re-adjusted the floats,re-set the curb idle,re-timed the motor,and re-adjusted the pressure. No probs since. Also, a friend put a 406 sbc in place of the V6. He couldn't drive more than a few mins either. A friend of ours asked if he had a vented gas cap. He put one on and had no probs since. I am using 3/8 lies from the tank to the reg & 3/8 from reg to the feed the carb. Future plan is to use braided lines of some sort.

my problem is that i set my fuel pressure at 58lbs, and while driving i have no issues, but when i go WOT the fuel pressure drops to 40lbs...i'm either:
-running out of fuel due to not enough fuel pump or feed line.
--i have an aeromotive tsunami pump with a sumped tank, -10 line going to the pump from the tank and -8 line going to the front of the car from the tank. the proper 12304 pre-filter is in place and working correctly...i highly doubt it's a fuel supply problem.

-the fuel pressure regulator is mismatched (high possibility) and is actually giving me a false pressure setting at idle and cruise, but shows it's true colors at WOT.

-the tank is not vented correctly and it isn't replacing air fast enough for the fuel being displaced by the fuel pump supplying it to the engine. i don't think this is the problem as currently the tank is being vented by an open 5/16" hose (think fuel tank vent valve tube on factory thirdgen tank, sans the actual valve)

is this all the time, or only when hot?? I have factory sumped tank and a bunch of aftermarket stuff as well..

seems like i have more problems when it's hot than when it's cold...can't say i've gone out and hammered on the car with it stone cold yet...

okay, my problem is similar...what happening to mine is the fuel is turning to vapor and pump not running effeciently....what I did was pull down exhaust and muffler, sprayed ceramic coating spray on those, then put one of those heat shields on bottom of tank (keep heat away from muffler), and then replaced that stupid plastic factory vent thing (front left corner of tank, it's white usually), and that helped me a ton...mine worked fine cold or if cool out, but if Tank got warm, I lost fuel pressure....don't know if yours is doing same thing or not, but maybe that will help, couldn't hurt.

what's your return line size? if you make it run the proper fuel psi at wot what happens to the base fuel pressure? Try running the tank at about 1/4 full and leave the cap off, best vent possible and see if the problem still exists

-6an return going back to the factory feed line at the tank. aeromotive said the line size is sufficient.

i haven't tried to adjust the fuel pressure any higher at WOT yet.

you run a lot higher pressure than I do....I run factory psi....it's possible your outdoing your pump too.....to compensate run bigger injectors with less pressure....(you probably know that though, lol)

i am running an ls1, the motor is supposed to run these kinds of pressures, and the tsunami is supposed to be able to pump 350lbs/hr at 70psi on 13.5v

does anybody know what the part number on that little plastic tank vent thing is, I've tried to get one but when I try explain what I need at the local parts stores they just look at me like I am retarted or something.

i think i'm using the factory vent...might be using one of the factory feed or return lines as a vent as well...just leaving it open...not safe if the thing rolls but ... ya

the official nomenclature is "fuel tank vent valve" and i know that O'Reilly cannot get their hands on it. (i work there and called the tech dept. yesterday) so right now i'm thinking maybe NAPA or the dealer...

I run a stock vent in mine, though there seems to be a surplus of pressure it is working fine. I use that big Summit inline pump, think its a copy of the A1000.. I use a single trickflow inline prefilter and 45psi.. If you feel your problem is vent, pull the cap and try to make a pass?? That will tell you right away..

ok, i don't think it's a venting problem, though it might be effecting it SOME. i rode around for about an hour without the fuel cap off and here's what i found:

-with the cap ON the fp would start out at 58lbs, and as the car warmed up, the pressure would drop ever so slightly, to about 56lbs or so. WOT would drop the fp to 40ish

-with the cap OFF the fp is rock steady at 58lbs, no matter how warm the car gets. WOT only drops to 48ish or so. cruise and light acceleration through traffic and it's solid at 58lbs no matter what. WOT is inconsistant though. before it would drop to 40ish nearly every time. with the cap off it would do as low as 40 and as high as 50, and i noticed as the car accelerated the pressure would come back up, but never get to the preset 58lbs.

oh, and the car seems to like the 4.11's much better than the 4.56's...it pulls like a freight train all the way to the 6200rpm rev limitter in 3rd gear...i'm gonna raise the limitter to 6800 and see what that does as well. these things are obviously unrelated to my fuel system stuff though...

Possibly that pump isn't keeping up to fueling demands at the hit or your regulator is slow to react to bring the pressure back up. The only company I use for EFI pumps and regulators is magnafuel, never have a problem with their stuff, it is the most expensive but it's the best. Raise the base pressure and see. Or hookup a wideband to check.

It's not a return issue, as that would create and over pressure situation, not an under pressure. The regulator responsiveness could effect it some, but I think it changing while you had the cap off is a sign.

I have always been told you need to vent as much as you feed. Although air will displace easier than liquid, 5/16 vent with a -10/-8 feed isn't very much vent volume. I would think that at low load/rpm the return amount is offsetting the vent's inadaquacy(sp?) but when you go WOT it's not returning nearly as much and the 5/16 isn't keeping up.

It may be, with 4.11's it will not rev as quick allowing fuel more time to keep up.. maybe

what kind of regulator are you running?
i was thinking the '99+ fbody cars had the regulator on the tank.

is there a vacuum line going to the regulator?

no vacuum line going to the regulator, it's an aeromotive regulator p/n 13301, it's the Universal Bypass Regulator. it comes with a spring for 3-20lbs installed, and a spring for 20-60lbs in the box.(obviously i've gone to the higher psi spring) i was told by aeromotive that it's actually not the right regulator for the pump. they told me this while having the second conversation with them, the first conversation i had with them they stated it would be fine...

this is the regulator:


as you can see it does have a vacuum port on it, but it's intended to reference boost for boosted applications where fuel pressure needs to increase when you get into the boost.

i wouldnt think that regulator would have an issue. it sounds like there may be something wrong with the pump for whatever reason. or the fuel filter is clogged up maybe.....

filter is clean, pump just got back from aeromotive for a check up, it's fine...

do you still have your stock FPR on the rail still or do you have 2 seperate fuel rails now when i did my swap to external i run a mallory 110fi the stock FPR wouldn't let me adjust it kept taking over so i removed all the parts in it to remove the problem i was having

? what FPR on the rail? the car has an ls1 swap (it was originally a 3.1, then had a carbed sbc in it) with a sumped tank. -10 line going from the sump to the Aeromotive Tsunami fuel pump, -8 line from pump to regulator, -6 return line. i'm not using any of the stock fuel system at all, for anything.

what kind of fuel rails are you running?

stock ls1 rails. there is no fpr on them.

sorry thought it was a tpi my bad not to fimiliar with the ls1 what controls FP on those cars ?

it's a returnless style system in the ls1 cars, i believe it's actually regulated at the tank.

i cant think of any other possibilites... unless its the regulator.
i run an a1000 pump with an a1000 regulator and it works great. i also run a regulator like the one you have on the side of my dedicated nitrous fuel cell. actually my nitrous cell is operating the way your car is im guessing. the 255 pump supplies fuel up to the regulator which then is bypassed back into the cell. i have a -4 braided line running from the other side of the regulator over to my fuel noid. (which would be the fuel rail in your car)

with that system i have not noticed any pressure changes, whether its hooked to the noid or unhooked and dumping into the fill hole on the cell. pressure never moves on the gauge. (although im only running 5.5psi on mine)
maybe its possible the tsunami pump is overworking that regulator, as hard as it is for me to believe.
is the adjuster screw nearly bottomed out in the regulator in order to get your 58psi? if so, maybe that spring isnt stiff enough and is causing some problems...

Have you hooked a vacuum line to the regulater to see if that does anything ?Because every car I have ever worked on the pressure goes up as throttle opens to keep fuel to the engine . Try hooking vacuum to it and adjust the base pressure and see what you get .

i am not using the vacuum port on my a1000 regulator either. stays at 43# the whole pass.

these regulators don't work the same way as a factory regulator does. that port is designed for refrencing boost, not refrencing vacuum. i know that by giving it a vacuum refrence that i'll either see the opposite results, or no change at all.

the tech at Aeromotive said that the regulator i'm running is designed for a low pressure, high volume situation, like what you'd see on a nasty carb'd setup. but why it includes a spring in the box for high pressure is beyond me. he told me i need to be running the 13109 regulator, which is this one:



but it's another $135 that i'm not really interested in spending.

the really crazy thing is that my AFR is totally unaffected by it now.

It wouldn't hurt to try it would it ? I'm just trying to remember how the boost would affect the regulator from my experiance with a '87 Thunderbird Turbocoupe I had . I think with boost you would still be using vacuum for the refrence or would you be using the boosted air for refrence ? I can't remember .

you use positive manifold pressure for the boost-reference (aka: boost) not negative manifold pressure (aka: vacuum)

Thats what I thought .

EDIT: never mind, re-read what you have for a fuel system and my theory of too big of a supply line isnt right. Thought you had 10AN feed to the regulator and that the pump cant keep up with that high volume. WOuld have suggested 6-8 an feed since EFI cars dont need big lines due to higher pressures. But I see you already have 8an.

Maybe its a combination of the regulator spring and venting issue. I would look into that spring and vent the tank abit better than closed cap, and go from there

my theory is a combination of the venting and the regulator as well...just needed to hear some more folks agree with me on that one after an intelligent conversation. i'm going to work on the venting some more before making a trip to summit.

matt, i think i am using the same type vent as you are as well. and i am returning fuel back through the factory supply line coming out of the tank.
i have a -10 supply with a -8 return.

Hmm...I'm going with the guys who know....sell of your current regulator and use that $$ towards the new one. Save the headaches and the hassles.. I was curious about that after I started reading, if you were already at at almost the top end limit of the regulator, before you stand on it and ask it to give more...I know that it is easier said than done, but drop the coin on the new regulator and be done with it.