Excessive fuel tank pressure/vaccuum...

[kylereece22]

Hello all,

I have been searching the forum for information regarding this issue and have found some excellent data. I just wanted to clarify a few things before I get started.
For the past few months the car has had a considerable amount of air either escaping or entering the gas tank via the cap.
After driving I often a small hissing/whistling noise from the cap and when I remove it there is a pronounced "whoosing" or air.

I do not really notice any gas smells though. My question is where is the charcoal canister in this car? Also does anyone have any suggestions regarding this issue?

Thank you!:thankyou:

 

[jimtash]

Lower left front side. Sounds like the canister purge valve is stuck open.

 

[rubydist]

its not clear to me how a purge valve stuck open would cause those symptoms.

it is possible that a purge valve that never opens could cause that, but every time I have seen that there has been a fuel smell either when removing the gas tank cap, or from the engine bay. it is possible that this just started, so the charcoal canister is not yet saturated, so no fuel smell.

I suggest bypassing the purge valve (just take it out of the line and put a connector between the 2 hoses) and see if that changes your symptoms. if it solves it, you can just leave the canister purging all the time. I had at least one car in which I did this and I never had any problems passing emissions tests.

 

[jimtash]

What you're suggesting is why he's experiencing his problems. The purge valve is stuck open to a constant vacuum draw. The system is sealed but not designed to have a continuous vacuum pulled on it. His problem is so much vacuum is being drawn into it that it's escaping from the gas cap seal when the engine shuts off. That's way too much.

 

[rubydist]

Except that is not how it works. Even if the purge valve is stuck open, there is no more than 1" of water vacuum drawn on the tank, because the location where the line enters the throttle body is a small opening.

And, as soon as the engine is turned off, there is exactly 0 draw on the gas tank, because the vacuum is removed and there is no check valve to hold it. It is quite literally impossible to shut off the engine and get to the gas cap while there is still a vacuum pulled on the tank.

Edit,

Oh, and I failed to mention that while the cap holds pressure, it has a check valve that allows air to get sucked into the tank - so that as the gas level goes down, air is allowed in to fill up that space.

 

[kylereece22]

Hey guys,
Thank you very much for the assistance. I think I will try bypassing the purge valve and then if that does not solve it I will look into the other options.

Like I said, I do not notice any smell in or around the car until I actually release the cap, and then I get a slight smell and the end of the cap is wet.

I 'THINK' it is pressure and not vacuum but to be honest I am not sure...

Thank you very much for your help I appreciate it alot!!
:thankyou:

Oh and I forgot to mention I did pass my emissions test recently and the cap is fairly new and was tested on their little cap testing device and it passed no problem...

 

[kylereece22]

Hey all
I am just wanting to confirm the location of this fuel tank purge valve...
Is it the one between the intake and the firewall (just behind the intake).
I think it is but just want to be sure...
Thanks again.

 

[jimtash]

No. The canister is located next the radiator on the left side. The valve comes right off of it and the hose feeds into the front top of the intake right next to the throttle body. What you're describing is the solenoid valve that controls the intake butterflies.

 

[Fordlover96]

To further add to that, the solenoid is about the size of a cigarette lighter and should be on the drivers side, right behind the radiator. Once you get in there, you'll see it.

 

[GEN 3 SHO FAN]

Hi,

I have a trouble with mine (96) and I found your post. I think it's a little related.

When we change the gas tank last summer (too much rust on it) the dealer doesn't sell the good one for me (needs 3 holes on the top) and sold me a 2 holes (97+) we remark it only when all was unbolt... We put the new one, retreiving the sensor on the 3rd hole. That gives me rapidely the code P0453 (Evaporative Emissions Control System Pressure Sensor High Input). Seems to do nothing on road as it is a emission code. Some times later, I remarked that when the motor goes near 4500-5000 rpm he have a big loss of power with hesitations but no misfires (8 new plugs, 4 news rears coils and no code for that). I tought first it was the trans going away but it's shift correctly in others rpm ranges.

Is the regulation of the fuel pressure by the PCM can have effects of that importance ? When near at WOT the pressure in the tank must draw substantialy and if the car think the pressure is high and opens the valve all the time (creating a vacuum to the intake IIRC), can this have a negative effect on the pump trying to send fuel to motor ?

Thanks for your help,

 

[pjtoledo]

Hello all,

I have been searching the forum for information regarding this issue and have found some excellent data. I just wanted to clarify a few things before I get started.
For the past few months the car has had a considerable amount of air either escaping or entering the gas tank via the cap.
After driving I often a small hissing/whistling noise from the cap and when I remove it there is a pronounced "whoosing" or air.

I do not really notice any gas smells though. My question is where is the charcoal canister in this car? Also does anyone have any suggestions regarding this issue?

Thank you!:thankyou:

in the evap/emmissions system there is a small plastic tube/splice in the vacuum line going to the tank, its under the radiator. there is an orifice in that tube to restrict the quantity of air/vapor that passes from the tank to the engine evap stuff. your orafice is clogged and cannot relieve pressure in the tank. clean, but do not enlarge, the tiny hole inside that plastic piece.
at least that's what usually happens on the V6 SHOs

Perry

 

[shobote]

X2 on the above. I ran a pin through it to open the clogged hole, and no more whistling.