Problem filling stock tank?

My 4th gen still runs the original 15.5gal metal tank from the factory, but with a new-in-2012 delphi pump/sender assembly.

Lately I've noticed it has gotten increasingly difficult to fill up the tank after a session. I'll see the fuel gauge (stock sender going to the IQ3 dash, so I'm seeing the actual, unbuffered reading) go down after each session, but after 30 minutes of sitting I can barely get 1/2 gallon (when it should take multiple gallons) into the tank before I completely fill up the filler tube (with the fuel sender still sitting lower than full).

I've revised the fuel venting setup multiple times since this issue has become noticeable, with the latest iteration being both the 3/8" and 5/16" teed into a straight 1/2" hose, with no improvement/change. At ECR I even some vacuum on the vent hose to see if I can get the tank to "burp" and take more fuel, to no avail. It really takes it sitting for quite a while for it to be able to take more fuel.I've resorted to having to wait a couple hours for it to cool off, then jacking up the LR corner to get any reasonable amount of fuel in.

Is there a valve or something else inside the tank that's causing this?

Some, if not all, modern cars have a one way valve in the filler neck or tube to prevent fuel leaking out if the car becomes inverted. This could be stuck "closed" for some reason. Some cars may certify to this standard with the feature built into the gas cap itself.

4th gen have a check ball in the neck about 12 inches down. I have seen them get stuck. It pressure builds it will stick. Sounds like your problem for sure.

I thought it was common to bash them out on our cars? Mine doesn't have that valve anymore and the mouth has also been hogged out to fit a giant ass funnel down there.

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Originally Posted by GlennCMC70

4th gen have a check ball in the neck about 12 inches down. I have seen them get stuck. It pressure builds it will stick. Sounds like your problem for sure.

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Yeah from what I've heard/read, sounds like it.

Did you end up having to replace your tank because of this, or can I punch this device out? Having trouble finding solid info online about it...

I only knew it was there cause we had a similar issue with a new car build with the tank improperly vented. Ran a aluminum rod down the neck and the sudden pressure release blew fuel out the neck and all over me.
I have not modifed that part.

Guess I'm gonna take a long rod and try punching it in.

This will be an experience you have never had before so take it slow!

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Originally Posted by Wade

This will be an experience you have never had before so take it slow!

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Nice.

What about issues when racers do this and then their car spews gas out the side or back when on track? Seems to me that would be a fire hazard but also could cause a slick spot on track. I have seen this before and mentioned it to a racer who just brushed me off with it. Should we be concerned?

Tilton-forgot to tell you this but I saw your car spewing gas out the back.

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Originally Posted by BryanL

What about issues when racers do this and then their car spews gas out the side or back when on track? Seems to me that would be a fire hazard but also could cause a slick spot on track. I have seen this before and mentioned it to a racer who just brushed me off with it. Should we be concerned?

Tilton-forgot to tell you this but I saw your car spewing gas out the back.

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A number of people came over to let me know. I didn't think it was as bad as some were saying because the car wasn't using much more fuel than normal. Looking at Sean's R4 video it was quite a lot during the long left hander before the front straight.

First we thought it was a clogged vent line from when I went off early Saturday. After inspection the vent line was fine, but the problem seems to be my exhaust (without turn downs) which was heating up the gas tank. This will be changed before MSRC as well as a new gas cap.

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Originally Posted by BryanL

What about issues when racers do this and then their car spews gas out the side or back when on track? Seems to me that would be a fire hazard but also could cause a slick spot on track. I have seen this before and mentioned it to a racer who just brushed me off with it. Should we be concerned?

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I'm unsure if removing the inlet check valve would cause an issue with my non vented cap if the tank is getting sufficient pressure venting on the other side.

To date, with my new venting setup that went in over the summer, I've no longer had issues with dumping on track, until this past event at MSRH.

Prior to MSRH, I was running a 3/8" hose to the bottom of a steel 1qt catch tank, and a combination of 1psi check valves at the top (one going in, one going out, both go to a breather hose on the back bumper), with a 3rd fitting going to a ball valve that I would open for venting during fueling. I had zero issues with dumping fuel on track (out the hose or cap), but then I took the overflow tank out and went to 1/2" hose as a misguided attempt to fix the fueling issue. According to Sean, I ended up dumping on track during the 30 min race because I had stuffed/overfilled the hell out of the tank and had no overflow. The overflow tank will be going back in before Cresson. I'll also return to having sufficient coiling/looping of hose to prevent a siphon effect...

I don't like dumping fuel on track either, it's a waste of money! Who cares about accidental combustion...

Tilton-it was a pretty good spray that I saw in the same spot you mentioned.

Pranav-sorry I really don't grasp all the catch tank venting stuff you have going on. Don't really know why you are having trouble other than it seems like it all may have been messed with. Don't really see any issues when using the stock tank. Now what I did think I understood is you have a catch tank for GAS mounted somewhere with the breather hose going to the back bumper. I've burned enough hair off my body to know that some gas fumes with a hint of spark are going to blow up-so to me it is concerning that you have a hose full of gas fumes on your back bumper where you might get hit causing a spark or underhood fire from the car behind you. Also, guess its good that Burch isn't smoking cigs while racing anymore.

That being said I have zero idea how the stock tank works for venting or anything but I have a stock plastic tank in the backyard I'll check out this week.

I won't name names but there are plenty of others here that have a straight hose going out back to a breather as well.

My overflow tank with 1psi valves stopped it from from spraying out all over the track and kept the situation pretty well contained for the 2 events I ran it. Only ripped it out for MSRH because I thought it was causing my fueling issue, which it wasn't (I manually flip a big ball valve to make a straight, unrestricted vent which bypasses all that crap when fueling in the pits).

Fumes from a hot tank on a return style fuel system have to go somewhere, they don't just disappear into thin air. Do you know where your tank fumes are going?

Only other solution I could think of is we all start running the factory EVAP hardware again.

The stock system uses the evap to run the fumes into the air intake, buring them. There is an air INLET valve (read as 1 way valve) that is OEM. The one for a 4th gen is a white plastic part at the end of a hose leading up to the tank. This allows air to replace burn fuel to prevent a vacuume being pulled on the tank.

I have this plugged on mine. It is only needed if the OEM evap system is in place. My evap line now runs to along the frame rail to the rear of the chassis. I have a small K&N style filter on the end that is made with a stainless mesh over it. It is a 3/8" line. This is plenty of volume for air in/out. It is high and centered. I also have a ball valve inline to close this vent off while being stored in the garage.

Don't run a vented cap on 4th gens. I have had major spillage w/ them.
I wouldn't knock out the ball at the bottom of the fill neck. My wish it was still there if you find yourself upside down.

I have plans to cut the OEM neck off and using fuel cell filler neck hose and a non-OEM cap to stop the leaks at the fill cap.

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Originally Posted by Pranav

Fumes from a hot tank on a return style fuel system have to go somewhere, they don't just disappear into thin air.

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They don't? Somebody better alert the EPA.

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Originally Posted by BryanL

That being said I have zero idea how the stock tank works for venting or anything but I have a stock plastic tank in the backyard I'll check out this week.

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The LS1 plastic tanks have all kinds of voodoo magic going on that I don't understand, good luck with that.

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Originally Posted by GlennCMC70

I wouldn't knock out the ball at the bottom of the fill neck. My wish it was still there if you find yourself upside down.

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Was there a solution to that car you said earlier was having an issue with the ball valve or should I be looking into replacing the tank?

Currently running a non vented cap, have had no issues with fuel coming out the gas cap since I made that switch.

Nevermind, I get what you were saying Glenn. Going to try play with some stuff when I get back to the garage later this week.

Bryan just for you I'm going to heat the tank up with a blow torch as part of my testing process. Don't wanna idle the car to simulate it, gas isn't cheap.

Now you guys have me thinking because my car really reeks up the trailer. My "vent" is the factory hose zip tied to the filler neck next to the cap. Did the LS1 tank use a rear-mounted evap can?

The evap can on 99-02 fbodys is located on top of the tank.
LT1 cars have it on the driver side behind the rear tire hidden by a plastic shield.

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Originally Posted by GlennCMC70

The evap can on 99-02 fbodys is located on top of the tank.
LT1 cars have it on the driver side behind the rear tire hidden by a plastic shield.

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Are V6 cars the same way? I'm kinda thinking vented cap and vacuum switching valve, so it vents to atmosphere when the ignition is on and stays shut when off, but can still vent via the cap if I leave it in the trailer in the middle of summer.

Finally got in there and took out the check valves, now have a 1/2" hose to a 1/4" NPT fitting at bottom of the catch can, 3/8" hose 1/8" NPT fitting at the top of the can going under/back.

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Originally Posted by Supercharged111

Are V6 cars the same way? I'm kinda thinking vented cap and vacuum switching valve, so it vents to atmosphere when the ignition is on and stays shut when off, but can still vent via the cap if I leave it in the trailer in the middle of summer.

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With a solenoid shutting off on ignition kill, you could end up running into the same issue I did; what Glenn alluded to is what I've been running in to so far. Any slight amount of pressure can cause the fill valve to jam up. With my prior check valve arrangement, the tank always saw between -1 and +1 psi, which is likely why the fill valve kept jamming in the up position, because the it had +1 psi against it.

A simple manual ball valve is the way to go, just flip it for storage.

Hoping to get to TWS this Friday to test it all out...

My fill valve no longer exists, I was just spitballing a way to keep the car from reeking up the trailer so bad.

Are you running a plastic tank or metal? I have the metal, can't remove the fill valve.

Anyways at TWS with the new setup today, I was able to fill a hot tank up to 90% within minutes of getting off track, letting it cool off for a tiny bit let me get that last 10% in.

I'm happy; if I want any better performance for being serious about enduros, a fuel cell would be on order. This will work well for my purposes for now.

I have a metal tank.

I was black flagged during R4 for excessive fuel dumping.

I've got a number or ideas, but before i get into details of what all I've tried so far, what are all of the 4th gen, metal tank guys doing for fuel venting? Please post up, it would be of great help.

If the 98 tanks are any better, I have one at my shop.

My white 98 model has a metal tank but as far as I know it's all stock. I'll look to see. Though I'm worried about my fuel pump-once it's hot it whines more than I do around a campfire. Then this weekend the pressure would bleed down to 0 and I would have to cycle the key several times to get the pressure to come up. I believe there is a check ball somewhere but thought that may also indicate the pump is going out. Would like to just drop a later model pump out of my 02 in it but I think there are some differences? Anyone know?
Glad you made the weekend and didn't have any motor trouble.

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Originally Posted by Pranav

I was black flagged during R4 for excessive fuel dumping.

I've got a number or ideas, but before i get into details of what all I've tried so far, what are all of the 4th gen, metal tank guys doing for fuel venting? Please post up, it would be of great help.

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As you know, but neck is bashed open to fit a big mouth can. As far as the vent goes, it's just an open hose routed up and zip tied next to the cap. It never hisses when I take the cap off and doesn't dump on the track. Stinks the hell out of the trailer, but after seeing your asspain it seems like a small price to pay. With a vented cap, it seems to me I ought to be able to simply fit a vacuum switching valve in the vent hose and have it open whenever ignition power is on.

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Originally Posted by Supercharged111

As you know, but neck is bashed open to fit a big mouth can. As far as the vent goes, it's just an open hose routed up and zip tied next to the cap. It never hisses when I take the cap off and doesn't dump on the track. Stinks the hell out of the trailer, but after seeing your asspain it seems like a small price to pay. With a vented cap, it seems to me I ought to be able to simply fit a vacuum switching valve in the vent hose and have it open whenever ignition power is on.

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From what I gather at this point, I'm running into a combination of three issues; I have a 1/2" hose going down low out of the tank, and the final outlet of the vent sits below the the top of the tank where the vent hose starts; additionally the 1/2" hose starts off from both 5/16 and 3/8 vent fittings tee-d together, which is a no-no.

It seems like the 1/2" hose is pooling up and not allowing any fuel in fluid form to not get sucked back in when the tank cools off, and the output being down low initiates a siphon effect.

The correct way would be to ditch all that, cap the 5/16" port, run a long 3/8" hose up high and make sure the outlet is up high (like your setup).

The other solution would be to acquire and install all the stock EVAP hardware, but I was missing all of that from day 1, built the car from parts...

I would still recommend not running an electric solenoid (what's the short/arc protection internally in the solenoid?), but instead just have a simple ball valve you can flip when you store the car...

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Originally Posted by Pranav

From what I gather at this point, I'm running into a combination of three issues; I have a 1/2" hose going down low out of the tank, and the final outlet of the vent sits below the the top of the tank where the vent hose starts; additionally the 1/2" hose starts off from both 5/16 and 3/8 vent fittings tee-d together, which is a no-no.

It seems like the 1/2" hose is pooling up and not allowing any fuel in fluid form to not get sucked back in when the tank cools off, and the output being down low initiates a siphon effect.

The correct way would be to ditch all that, cap the 5/16" port, run a long 3/8" hose up high and make sure the outlet is up high (like your setup).

The other solution would be to acquire and install all the stock EVAP hardware, but I was missing all of that from day 1, built the car from parts...

I would still recommend not running an electric solenoid (what's the short/arc protection internally in the solenoid?), but instead just have a simple ball valve you can flip when you store the car...

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My car has the stock check valve, vented to the atmosphere with a standard gas cap. Haven't had any issues.

Plugged the 5/16" outlet as recommended, ran what felt like 20ft of 3/8" hose looped up a million times, and ended it up high above both the tank and the filler neck to avoid a siphon effect.

I think I've done enough, this better work.