Excess Air (?) Fuel Pressure

[808state]

i've converted my 80 corolla (te72) from a carb setup to an efi setup. below is a diagram of my fuel system setup. i basically ran a new fuel run into the fuel rail from the fuel tank. then from the fuel pressure regulator, utilized the existing original feed and return fuel steel lines back the he fuel tank. the problem is this. i seem to be creating a lot of excess air (?) pressure in the system. there is a 3rd smaller steel line from the gas tank that originally went to emissions/charcoal canister that i had removed and capped with a rubber cover. after i drove around for a little while, fuel was squirting out of this until i opened the gas tank cover which seemed to have a lot of pressure.

my question is this. for people converting from a carb fuel system to efi fuel systems, what are you doing to control the excess pressure? in reading the megamanual, there's no mention of this in the fuel system. a google search, i found something like a gm vent valve 10033125 vent valve as mentioned here:
http://www.fordmuscle.com/archives/2008 ... /index.php

also read about vented gas caps?

anyone have the same issue if so, how did you solve the problem?

[devastator]

I converted from a carb with a vented gas cap on my tank, and I do not have this problem. Try installing a larger diameter return line than the line used to supply the fuel pump. The pressure will drop as fuel is "passed" through the FPR. As this fuel enters the return line it will drop pressure even further as it returns to the tank. The vented gas cap should take up the air pressure variation in the tank. None of this is emission legal, but neither is Megasquirt.
I used to return my fuel to a tee coming off of the tank that fed the fuel pump, not using a tank return at all. I changed this during a recent fuel troubleshooting crunch, but it was not the problem I was having and have recommended it to others as a simple EFI conversion option.

[808state]

thanks for the replies. i think my car has a short hose off the gas tank filler neck that went back to the tank. thinking of making a tee off this and vent it there and put a breather filter on it.

[bleoh]

Just a safety note, all your rubber lines after the fuel pump should be FI rated. If you get a kink or blockage downstream from the regulator it will see the max pressure your pump can support.

[808state]

bleoh-

was there a section in my diagram/fuel system that you'd recommend changing? all hoses (blue) from the fuel pump to the regulator are goodyear fi hypathon hoses.
http://www.goodyearep.com/ProductsDetail.aspx?id=5144

[LeslieTroyer]

I believe he is refering to the 5 non-FI rated hoses in your return line -- between the fuel-pressure-regulator and the tank... I personally ran 100% FI rated hose, I've seen too many car fires because of broken fi hoses...

[devastator]

Many return lines are not under any significant pressure, like mine, which dumps back into the top of my fuel tank.

[bleoh]

It is true that you want an unrestricted return line back to the tank so that is does not see any significant pressure. However, you still need FI rated hose and clamps in the return line because if it ever did become blocked or restricted it would be under pressure. All the fuel pressure regulator does is provide a variable restriction in the path of the fuel. The fuel pump does not care if that restriction is coming from the FPR or a kink in the return line back at the tank.

[808state]

i relieved the pressure by putting a t fitting and running a few loops around, then vented to atmosphere. this is just was by the gas tank. i don't smell any fumes even though it is vented to atmosphere. if it does become a problem, can try see if i can fit up charcoal canister. solved the excess problem. not sure about filling up the gas tank though, but we'll see.



in regards to the return line, yes, my return line is not fi rated, but if i'm not mistaken, it might be a bit more robust(?) than the plastic returns on the 2002 bimmers. a pretty good writeup that i read through a few times before i took the jump into efi.
http://www.finkbuilt.com/blog/fuel-inje ... -complete/

In its carburetted state, the 2002 uses a plastic (low pressure rated) fuel feed line. The fuel return line runs beneath the car, and for durability, is made of steel, so I did what others before me have done, and reversed the feed and supply lines using the steel as a high pressure feed, and the plastic line as a return to the tank. All flexible lines were replaced with proper high-pressure rated fuel injection hose.

another article i read up on before i took the jump was this one.
http://www.302w.com/Windsor_MegaSquirt_Part2.aspx

again, low pressure rated fuel line returns. basically, these two articles and was the reason i used the carb rated return lines.

what do the oems do? the newer cars are returnless though.

[devastator]

If the loops in your vent line, (off of the tee), fill with fuel in the low areas, they will not vent to atmosphere. You might consider running it straight up and putting a small breather filter on it to keep dirt, bugs and small rodents out.

what do the oems do? the newer cars are returnless though.

Beats me, my stuff is all old school.