24 replies to this topic

[DrDomm]

I got black flagged (twice) at a track day on Tuesday for fuel leaking out of the filler door.  I only started with half a tank of fuel.  When we opened the cap it seems that the tank is pressurized.  My car has always done this, but not like this.  Check out the video.  Any thoughts?

 

http://youtu.be/aKZCyEq8Ung

[NPiekarski]

Does your car have a modified fuel filler neck?

[HoneyBadger - BrianW]

There is a pressure control valve on the top of the tank. I would bet yours is bad. LInky:https://mazdamotorsp...ectionId=4200A#

[davew]

Items that can cause this;

1- gas cap

2- Small fuel lines going to filler neck not looped

3- roll over check valve in bottom of fuel filler neck stuck open or missing

4- charcoal cannister gone bad (possibly from 1-2 or 3)

5- stuck check valve for evap system

6- modified evap system, put back to stock

 

Dave

[DrDomm]

Hmmmm...well, I have a few things to look at I guess.  Thanks.

 

Modified fuel filler neck?  Yes, I believe so...per GCR.

 

But what's the deal with the gas cap?  That seems like the easiest fix.

[Jim Boemler]

We had one car that had an exhaust coupling come loose, which left exhaust being directed toward the fuel tank.  It ended up blowing the cap off the tank, very loudly.  Obviously VERY dangerous!  It would at least be worth a check on your car.

[davew]

The allowed modification of the fuel filler neck is to remove the unleaded fuel restrictor under the cap. This will have no effect.

 

At the bottom of the filler neck is a plastic trap door doohickey. These have a tendancy to stick causing slow fuel fill. Some people remove them, but this also allows fuel slosh to get up into the filler neck.

 

On 99s only, there are 4 hoses that go to the filler neck from the gas tank. The main fuel filler hose (2" diameter) the breather (1 inch diameter) and 2 small 1/4" hoses. The 2 small hoses should be looped back onto each other. Hose one should go from the nipple on the filler neck to the other nipple on the filler neck. The second hose should go from the nipple coming out of the tank area and go to the other nipple from the tank area. This is also allowed. Note that this applies only to 1999 cars, NA and 2000+ do not have these hoses.

 

Dave

[Ron Alan]

The allowed modification of the fuel filler neck is to remove the unleaded fuel restrictor under the cap. This will have no effect.

 

At the bottom of the filler neck is a plastic trap door doohickey. These have a tendancy to stick causing slow fuel fill. Some people remove them, but this also allows fuel slosh to get up into the filler neck.

 

On 99s only, there are 4 hoses that go to the filler neck from the gas tank. The main fuel filler hose (2" diameter) the breather (1 inch diameter) and 2 small 1/4" hoses. The 2 small hoses should be looped back onto each other. Hose one should go from the nipple on the filler neck to the other nipple on the filler neck. The second hose should go from the nipple coming out of the tank area and go to the other nipple from the tank area. This is also allowed. Note that this applies only to 1999 cars, NA and 2000+ do not have these hoses.

 

Dave

A picture says a thousand words...got one Dave??

[FTodaro]

The allowed modification of the fuel filler neck is to remove the unleaded fuel restrictor under the cap. This will have no effect.

 

At the bottom of the filler neck is a plastic trap door doohickey. These have a tendancy to stick causing slow fuel fill. Some people remove them, but this also allows fuel slosh to get up into the filler neck.

 

On 99s only, there are 4 hoses that go to the filler neck from the gas tank. The main fuel filler hose (2" diameter) the breather (1 inch diameter) and 2 small 1/4" hoses. The 2 small hoses should be looped back onto each other. Hose one should go from the nipple on the filler neck to the other nipple on the filler neck. The second hose should go from the nipple coming out of the tank area and go to the other nipple from the tank area. This is also allowed. Note that this applies only to 1999 cars, NA and 2000+ do not have these hoses.

 

Dave

Not to mention that little Doohickey in the filler neck would keep gas from running all over you if the car rolled over. vary easy to disassemble the filler neck and check the check valve. Worth spending some time to make sure its functioning correctly. Did I mention that risk of fire is what I fear the most?

[ChrisA]

I got black flagged (twice) at a track day on Tuesday for fuel leaking out of the filler door.  I only started with half a tank of fuel.  When we opened the cap it seems that the tank is pressurized.  My car has always done this, but not like this.  Check out the video.  Any thoughts?

 

http://youtu.be/aKZCyEq8Ung

Are you certain the sound is from air being pushed out when you loosen the cap and not from it being sucked in? If pushed out, there should have been a pervasive smell of gas fumes. If you have a non-vented gas cap or a faulty one, the tank can create a vacuum from either the fuel & air condensing from a temp drop or from fuel use. The cap should be designed to allow the tank to breath in when needed and the evap system to allow it to breath out when needed.

[DrDomm]

Are you certain the sound is from air being pushed out when you loosen the cap and not from it being sucked in? If pushed out, there should have been a pervasive smell of gas fumes. If you have a non-vented gas cap or a faulty one, the tank can create a vacuum from either the fuel & air condensing from a temp drop or from fuel use. The cap should be designed to allow the tank to breath in when needed and the evap system to allow it to breath out when needed.

 

Yeah, I'm sure...part of the problem was fuel leaking OUT of the cap/door.  

 

Dave, thanks.  I will look at the hoses this weekend.

[RazerX]

The allowed modification of the fuel filler neck is to remove the unleaded fuel restrictor under the cap. This will have no effect.

 

At the bottom of the filler neck is a plastic trap door doohickey. These have a tendancy to stick causing slow fuel fill. Some people remove them, but this also allows fuel slosh to get up into the filler neck.

 

On 99s only, there are 4 hoses that go to the filler neck from the gas tank. The main fuel filler hose (2" diameter) the breather (1 inch diameter) and 2 small 1/4" hoses. The 2 small hoses should be looped back onto each other. Hose one should go from the nipple on the filler neck to the other nipple on the filler neck. The second hose should go from the nipple coming out of the tank area and go to the other nipple from the tank area. This is also allowed. Note that this applies only to 1999 cars, NA and 2000+ do not have these hoses.

 

Dave

Dave, what do the 2 1/4" hose do (i.e. where do they go?)  

[Johnny D]

Dave, what do the 2 1/4" hose do (i.e. where do they go?)  

 

He asks the best questions.

J~

[RazerX]

Easy Johnny....

 

I don't have a fuel diagram handy and just wonder what the function of the two 1/4" vent lines are for.  Given they are not on subsequent 01,02 year models they must have been replaced or done away with.  It is an engineering disease, we often want to know why....

 

sheesh...

[davew]

First, this only applies to 1999 model cars. Not applicable to 2000 or newer. nor to 90-97s

The 2 lines that come out from the gas tank area do NOT go directly to the tank. they are part of the evaporative emmisions system. What I think happens is when you have fuel slosh going up into the filler neck on cornering, some of that fuel goes into these evap lines. Which would normally only have fuel vapors in them. When liquid fuel gets in the lines, it eventually gets into the charcoal cannister near the right rear wheel. Eventually the canister fills with fuel and the tank can not properly vent and/or the fuel leaks out of the cannister. If the canister fills completely, the fuel will get into the canister under the hood behind the right headlamp. This will cause the engine to run poorly.

Looping the hoses eliminates any possibility of fuel getting into the canister this way. Yet the system still functions properly. getting liquid fuel in the canister will ruin the canister. It should be packed with granular charcoal. If it rattles the canister is junk.

Dave

[RazerX]

Thanks Dave.  Understood.  

 

is the rattle test valid for both the rear and front canisters?

[ChrisA]

The front canister (on a 99) is just a vapor store tank, I don't believe there is anything in it, but I've never cut one open either, so...

[davew]

The front canister (on a 99) is just a vapor store tank, I don't believe there is anything in it, but I've never cut one open either, so...

 

Correct, the front is simple an empty catch can

[Johnny D]

Easy Johnny....

 

I don't have a fuel diagram handy and just wonder what the function of the two 1/4" vent lines are for.  Given they are not on subsequent 01,02 year models they must have been replaced or done away with.  It is an engineering disease, we often want to know why....

 

sheesh...

 

It's all good. Glad your asking, Dave and the guys give great answers, we all learn, and it leeads to others things.

I'm a Mech Designer, see objects in my head in 3D.

 

I don't think I'm counting but..

 

Cam Shimmed

Wheel lock removed.

Alignment string

Clutch bypass

 

If you're fixing as you go, you should have a nice piece.

Keep it up!! See you at the track.

 

That goes for you lurkers out there too.

J~

[RazerX]

My car is a constant project.   I have a fair bit of mechanical experience but I am open to learning all the time.  And there are some very experienced Zen masters here who share information.  

 

Since our last time on track i have swapped rear uprights, 4 shocks, diff, rear subframe, brake line, rerouted fuel 1/4" fuel lines per Dave, currently putting a sleeve on my crank to stop the massive leak caused by a crevice on the crank.  None of it was damaged from the weekend.  Nor will it make me faster but i have been battling something not be square or right in the car.  Hopefully I will get a more consistent setup and tweak from there.