After driving for a while, opening the gas cap to fill the tank, there's a big suck of air into the tank. Is this normal? Anybody else notice this? I'm using a Stant locking gas cap.

 

Its not a "suck" its a release of pressure that builds up in the tank.

My car always did that when I had intank pumps.

 

When you don't have "the big suck", we may have a problem

 

Its not normal. The gas vapor remover (EVAP) system is not drawing the fumes and pressure out of the tank. If its not a solenoid problem on the right side of the intake, I will guarantee that the plastic vapor line from the EVAP canister is clogged up with charcoal particles from the EVAP canister. This happens when a filter in the cannister tears and releases the particles.

You need to replace the cannister and clean the vapor line out to repair it or bypass the EVAP all together. If you do bypass it, you will need a venting gas cap and be prepared for it to smell gassy like a 60's car.

 

Just to clarify, when I unscrew the fuel cap, air is drawn into the tank around the cap. It’s not a release of pressure out of the tank, it’s like a vacuum.

If I am to understand what’s being said here, the EVAP system is supposed to draw air & vapors out of the tank. If this is the case, OK, it seems to be working as shown by the vacuum the tank has when I open the cap, but how or where is air supposed to go into the tank to replace what the EVAP system is drawing out at the other end?

Thanks boyz....

 

I've never encountered a tank that is vacuum sealed like that :\ All the vehicles I've delt with have pressure built up. My 91 TPI, my 93 LT1, my 64 Ford Army Jeep, 94 Park Ave, 2 90 Suburban and even my DD 90 Carolla. All release pressure :\ So either WRD is incorrect in what he's told us, or all (with the exception of my Jeep) have plugged EVAPs. Now, I'll give it to him that all mine are 94 or older, but that's pretty high odds that EVERY one of them has a bad EVAP system... And yes, they had vented gas caps It's also all dependent on how long between cap removals, if I fill up just a few gallons one day, and then a few more days later, it's not too bad. However, like with my DD, it's around 2 weeks before I fill up again, so it's quite the build up of pressure.

With that said, and me experiencing pressure in many vehicles, I'd say that something is a bit odd with your car Paul. I say that only because you have to factor in not just the expanding vapor from the fuel, but that it is a vacuum being created (as you're adamant it is). So you have something that's pulling LOTS of gas (as in air, not fuel heh) out of your tank. Since we have metal tanks, do you have a 'pwomp' when you open it up, from the metal popping back into place? My Jeep does that, but it's from the opposite effect, since it's being pressurized, it's expanding the tank's sides, and they're then popping IN due to pressure rather than OUT from vacuum.

On the other hand... I do have a vague recollection of high volume pumps doing that, but I don't see a mention of one in your sig. Do you have one, and it's just not listed?

 

my car has done it...So, i just bypassed the EVAP crap, and drilled a 3/16" hole in my gas cap. Problem solved.

 

Ok guys, I’ll look into the EVAP system. Still, I’d like to figure out that if this is supposed to be a closed system and the system draws fumes into the EVAP, how is fresh air supposed to get into the tank to replace what’s being drawn out?

I’ll play with this tomorrow. After I fool with the new headliner. And fix the right window. And fix the rattle in the front. And look into the airbag light. The list never ends, does it?

 

my car does it, my parents camry does it big time, my dads GMC workvan does it, and my moms minivan does it when you open the gas cap. im pretty sure thats normal

 

^ Agreed. I'm no EVAP master, but with it being so hot down here (Florida) it builds pressure in the tank. When you remove the cap that pressure has to go some where. My 95 does it every time I fill it up.

 

Badazz, when you open the cap, it sucks air in?

 

The way i see the EVAP system is, it draws vapors to be reburned, either way, there has to be vaporization somewhere, its in the tank or cap or both, i did notice my tank has a vent line that goes out & just stops in open air, mine too creates pressure, more so if i don't open the cap for a week or so or the fuel is lower, but its more noticable in the summer months, BUT if you are exsperiancing a "vacuum" affect, something is not right & you need to look into it, the pump somehow is pulling in air around it sounds like, & its also possible the venting is not working good causeing the air too not release in the tank, you may want to check the "pickup" line in the tank for a hole, just like a straw with a hole in it, & if the tank isn't venting, the air will stay trapped untill you loosen the cap.

 

I described above precisely what happend to my car and what I did to resolve it. Yes it was a blowing problem. Pull the cap and air would gush OUT of the tank.

If its a sucking problem as described, I would imagine that the EVAP is working and there is a clogged vent not allowing outside air to enter the tank to replace the air being extracted again by the EVAP. The vent is a white looking thing about the size of a golf ball in front of the tank.

 

Hey wrd1972, looks like your explanation is feasable. I'll get under the car and have a good look for the thing. THANKS!

 

So this is it?: Part number: 10245442
http://shbox.com/1/fuel_pump_wiring.jpg

 

Yep thats it. It should let air in but not back out if its working right.