Insane fuel tank pressure

[billabongo]

Hi,

Longtime hovering and reading and now posting

So here it goes

93 4Runner 3.0 auto sr5 130k

Truck is near flawless and full service history up till dec las year.

Anyways, I live in vegas and its have been having a ton of issues with extreme fuel tank pressure build up.

Now whenI say extreme. I am saying if you take the fuel tank cap off it will vent for nearly 20 seconds at very high rate of air. The best way I can describe it is if you have a large air compressor tank and you decided to purge the tank, you would get the idea.

Doing this also causes the truck if running to run horrible and even stall if i remove the cap really fast.

Also if you start the tuck with the cap off the pressure in the tank is immediate and you can literally hear and feel the pressure at the filler neck and its loud.

So prior to this happening I was having really bad fuel fumes from the evap canistor.

I inspected all the lines, tested the valve per the service manual and blew it out. No issues noted.

I checked all the tank lines from front to back
I pulled the connections and blew air through them, all nice and clear.

I then suspected possible bad fuel pressure reg or pump.
So i put my fuel pressure tester on the rail tested out the system. No issues, 38psi with vacumm line on 45psi without.

I run a key off test and see that the fuel pressure drops off to zero. So bad fuel pump flowback valve or injectors leaking.

Tested out the system and found the fuel pump was draing back.

So using my trusty self made access panel under the carpet, swapped in a new fuel pump.

While there checked all hoses even ran the pump while in the tank so i could view for any crazy stuff.

No issues, fuel return line pumping it back in just fine pump not leaking.

So sealed the tank back up and try out the truck.

Same problems!!!
Though now the fuel pressure holds with key off.

So this time i figure it had to be a faulty evap canister valve and bypass disconnect the canister and cap the lines.

Try again, no change.

I am so stumped, It is such a violent pressure build up I am concerned the tank may literaly rupture, explode or blow the filler hoses.. You know something is wrong when your at a gas station and people stare at you when it sounds like your tank is expolding when you take the cap off lol

So ideas wanted, cause i am stumped.

(Posted from my Galaxy Tab)

 

[Iroke17]

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[Howitzer]

X2 on swapping return lines.

Fuel under pressure is never a good idea, and that's just aking for something to happen.

I Don't know what the diff is between 1st and 2nd gen assemblies, but it's gotta be a plugged line or something somewhere

 

[GonOvr]

Doesn't the tank have it's own vent line? I remember pulling my tank on my '92 and it had a line connected to a check valve on the cross member. I could be wrong since my power plant changed and it's been over a year since i messed with the fuel tank.

Here is a picture of mine, it is hanging in the middle of the picture.

 

[hoe_nah]

Upskirt LOL....SEXY

 

[Iroke17]

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[GonOvr]

What are those fans cooling?

Transmission coolers, ran them to the back to keep them as cool as possible. I have a pretty high stall torque converter and it likes to make a lot of heat.

 

[willis_bud2]

Subscribed!! Same problems but not all the time. Tank is under a decent amount of pressure it seems. I just noticed this the other day so I've been trying to figure out if it is during stop and go driving or long haul conditions. Keep ya posted.

 

[billabongo]

Sorry for the slow response. I have been busy working

Anyways, I realize most complaints I read for the pressure issue say that the return lines must be swapped.

I am not sure this is possible as my tuck has not had any work done to the fuel system or such that any of the fuel line or returns would have been tampered with.

On my 93, the eval canister has 3 connections. 2 on the valve portion, the larger diameter one goes to a curved hose to the steel return line that ia pointing straight up in front or the can. The 2nd one is the small vacuum line which runs to the thermo switch and then to the valve body on the intake. The 3rd line is the large line on the bottom of the can, which I have no idea where it goes.

The service manuals suck at showing line routing and locations etc for the evap and fuel lines.

Now I did bypass the eval can directly and using an adapter I hooked the fuel return connection for the evap can directly to the throttle body connection.

This got rid of the pressure problems but caused very hard starting as the vapor fills the intake plenum.

I have noticed while testing the system out that the fuel appears to be super hot, nearly boiling when it comes back to the tank and this explains why I have major pressure venting while the gas cap is off and the truck running.

This makes me very concerned as the fuel is nearly at flash point and can easily explode.

Has anyone encountered the hot gas problem? Now mind you my truck is nearly stock. No engine mods, the truck runs cool and never gets to the halfway mark on the temp gauge so I don't see why or what is causing the fuel to heat so much.

There are days I just want to burn it to the ground and this makes me really want to lol.

(Sent from my DROID x at 38,000ft)

 

[mikedks]

Unless you are the original owner of the Runner, you will never know what the previous owner has messed with. Anyone of those lines could have been switched years ago.

Anyway, when you start talking about fuel temperature being near flash point, it's time to pack it in and let the pro's have at it. My guess is that the Toyota dealership would have it diagnosed within an hour, system is just not that complicated.