When my car (89 350 Iroc) is hot 225 and up. I get a strong gas smell coming out of the left rear wheel well at idle. With the windows closed it will get into the interior and just smells like cr#$. The canister purge is working. I checked it with my Helms GM manual. The ECM is commanding as it should. I have a new "pressure relief" on the tank. It's a small white flying saucer looking thing mounted to the frame rail. I have noticed that if the car idles long enough I will get a loud "pshhh" as vapor releases from this valve. Why am I building so much pressure?
GW

 

You may need a new canister. If it is full of liquid fuel then it is done. It certianly won't accept any more fuel at that point, and is only capable of accepting so many vapors in the first place.

 

i had the samething happening to my gta but on my car it was a rip in the seal for the gas cap. if the car is tpi the return with build pressure and if that seal is ripped then you will smell fuel when the tank starts to pressurize.

 

If it was the seal, you should have the smell all the time.. Plus, your tanks pressure would be escaping through that. I guess thats a possibility.

However, I've come to a conclusion as to what the problem is. At least I think. The muffler under the tank can get hot enough to where not even the heat shield is adequate for protection. Basically, your system is functioning fine, but the muffler is heating it up to where the pressure raises. When this happens, it has to escape somewhere. The relief valve is there to get fresh air into the tank so it wont colapse. However, if the tank builds too much pressure, it vents it out, its a security feature. Now, if you were to move your muffler somewhere else, or just not run one to begin with, chances are that your tank wont have problems. This a chronic third gen problem. I know of two cars that had it in person, and a lot more that had the same issue on the net.

Also, chances are that everything is good on the tank, its just getting to hot and over pressurized. IMO.

Mine's doing the same thing.
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Oh, one more thing

Check to see if the line that goes to the canister is not plugged up. Mine was.

Didn't solve the problem, but it shed light on why I passed emissions.

 

Amendment to this, the problem is getting worse. The car just has to idle for a sustained amount of time and I get the fuel smell. It no longer occurs just when it's hot. My canister, purge valve, pressure relief valve are all new and functioning correctly. I thought about the heat problem last year and built two additional heat shields to attach to the stock one. I do think that the pressure build up is too high in the tank. Some time ago, about a year, when this problem first appeared I abruptly open the fuel cap while idling and liquid fuel sprayed out a foot or so and the engine quit. Put the cap back on and she ran fine, hasn't happened since. I still open the fuel cap slowly though. I haven't checked the line to the tank from the canister but I will. My understanding is that these tanks only should pressurize to 1 or 2 lbs psi. Is that correct?

 

Fuel tank vent valve is located on the drvr rear of the car. It lets air in to displace used fuel, might want to check it out, the do the same thing when failing.

later
Jeremy

 

Thats a lot of pressure. I've been trying to figure out exactly how exactly does the fuel pressure relief works on our cars. Too many conflicting reports.

 

The fuel tank vent valve (behind driver wheel well) was replaced with a new GM part. The fuel tank pressure control valve that is mounted near the charcoal canister is supposed to release pressure at 5kPa. It is supposed to release tank vapors into the canister which later can be purged when the engine is up to temperature and above idle. I'm going to crawl under the car today and check a few things. Sure hope I don't have a tank leak.

 

I can hear and smell the vent valve release underneath the car but I will check this out today, thanks
GW

 

Today's update
Fuel cap is good, the O ring is intact. Double checked the pressure relief valve per the diagnostics in the Helms manual and it is operating correctly. Disconnected the fuel tank to pressure relief valve line where it connects to the fuel tank and at the valve in the engine compartment. Blew through this and it is clear. The rubber hose connecting to the tank is clear and in good shape.
Connected a rubber hose to the hard line that goes into the fuel tank. I can blow through this but I can hear the air escaping. I can't see where, but it sounds external. This should vent directly into the tank with no external sounds. I'm thinking something is leaking up top of the tank.
Doesn't follow though with a high pressure problem...?
GW

 

Hmm... Well, did you check the bottom of the filler neck?? Thats where they usually develop the leaks. Especially the later models.

Still, if the vent is venting pressure out (which it should hold, its what its designed to do) than its highly impossible that you would have a leak.

I took the valve off on mine, and just used a carb fuel filter. Sure enough, the tank did not pressurize. I am not sure how pin hole sized leak would react to the pressure. It should be releasing it, and even if it does, its still waay too much pressure in the tank hence the valve releasing it.

You had the tank out?? Did you go through it to check for holes?? Did you think about the air escaping through the filler hole (because you did not have the cap on, or it was loose??). I am having the same problem, been trying to figure it out for a year. I just decided to go with a fuel filter for the time being so that too much pressure doesn't build up. I have the gas smell coming out still. Its by no means a smart thing to do (but I am not smart either). LOL.

I am glad someone else is trying to figure this out. i've been working quite a bit last few weeks, so I hadn't had the time to figure out the problem. So, I hope you stick with it, and we can get to the bottom of this.

 

Well I'm trying. I've been on it for some time. I was going to take the tank out and look things over but I noticed that the muffler shop welded everything together and I wanted to drive the car tonight. I don't see any noticable fuel traces from a leak. I did replace the small 6" rubber hose that connects the tank line to the canister hard line, it had a few cracks. I still smell fuel though.
It's got to be a tank issue, there is just not that much to the system and everything else is checking out. I'll post back with the next steps. Things that make you go hmmm....

 

I've looked under my car and found nothing to point me to the problem. I've noticed that one of the brackets that holds the fuel lines is really hot. It was dark and my flash light quit on me, but I had noticed that the bracket went over to the transmission, and was really hot. I'll check things over again once I have some sunlight tomorrow.

 

The 2 usual culprits:

Joint where filler neck meets tank is broken
Rubber hose pieces connecting hard lines to tank rotted

Odds are near 100% that it's one of those 2 things.

The tank is supposed to have pressure in it; that's not "the problem", by itself. In fact alot of cars will light the "check engine" light if the tank FAILS to hold pressure. You're wasting your time trying to make it NOT hold pressure, because if everything is working right, it WILL build up pressure of its own accord.

It's also possible that the tank has a hole in it; usually they get holes in the very lowest places, by rusting from the insde. Having a little water get in there and stay for a long time will eat right through the metal.

 

Yes, the tank will hold pressure, but too much pressure will result in fuel going places it shouldnt.

I went under my car today, after a long/hard run in 100 degree heat. Sure enough it smelled awful. I went under looking for problems (with a fire extinguisher and I think I've come up with a potential problem.

The muffler under the tank is really heating up the tank. My tank was so hot that I could barely touch it, and I can hear the fuel boiling inside. I was amazed and pissed at the same time. This is edelbrock 3inch cat back and it was so hot that I wanted to cut it off immidiately.

Also, I checked all the hoses and found where the smell was coming from. It was coming from the UFO looking relief valve. Now, i've removed that valve and used a fuel filter in its place because my relief valve would not let fresh air in the tank. It will vent it out, but the spring was messed up and it only worked the release way. I have ordered one from GM parts direct, but they just shipped it today . It took them couple of weeks. Special order item I guess.

Anyway, there was almost raw fuel in the fuel filter. It was moist but it didn't build up fuel. My guess is that the gas is boiling and once it moves to somewhere not so hot it turns into gas again... explaining the gas in the filter.

Is there a one way release valve. I am thinking of finding a valve that only lets air go one way. So that the tank has a supply of fresh air coming as the vacum sucks the fuel into the engine. This way it wont vent outside and it will keep the tank working the way it should.

 

Yup,

I got the muffler wrapped in exhaust wrap. Also wrapped the I pipe that goes over the rear end. Drove it around, and so far, so good. It was night though, so it was a bit cooler 79 degrees. LOL. She drove fine, and no smell yet. Keeping the fingers crossed.

 

TTT

So far, drove the car in 100 degree weather for about half an hour and no gas fumes. (Fingers crossed).

Tonight I am going through the lines to make sure they are all cool and are not getting heated up by exhaust and such. I think that might be the part of the problem.

 

So far, I smell exhaust, no fuel. Its been doing fine. Tomorrow I got the afternoon off, so I'll take pics of what I did and what I think the problem might be.

 

I replaced the short rubber line that is clamped between the hard lines out of the fuel pickup unit and the hard line that runs to the canister. This apparently did have some sort of a leak as I could not get it to hold vacuum.
This took care of the major smell. I still get a pressure release sound out of the "burp valve I'll call it" when outside temps are in the 100 degree range and I'm sitting at an idle, though it's not as strong. I have another line coming, the one with the brass fittings, to replace. I'm just going to replace it because it's not too expensive.

I'm thinking as another person trying to help did that the muffler is now heating up the tank and creating the pressure release. I had leaks and thus smell but the pressure is excessive. I may change my exhaust system and move the muffler behind the cat. I'll probably use a single chambered muffler such as what is offered by Classic Exhaust. I'll be able to wrap the exhaust pipes as they pass near the tank with header wrap then.
What do you think?
GW

 

Xlwhellraiser I'm sorry I didn't see that you did this. Hmmm... perhaps it will work.

I also want to thank all of you for the help so far!!! sometimes some of these problems are so hard to solve, such as this and rough start up idle.

by the way, newbie question, what does TTT mean?

 

To The Top.

Yeah, i get a bit of smell, but that is to be expected because I only have a fuel filter there and no pressure is held. Now, I got a brand new "burp valve" LOL. If you suck on it from the tank side you should be able to keep sucking air albeit a bit hard (hence pressure). Now, on my previous one I can suck air for a bit and than it gets really hard and stops. (Please keep a clean mind while I am describing this ).

I will replace the valve a bit later, take some pics of what I did and post them up.

I checked the muffler and it still was hot, but not as hot as it was before. Still, I don't like it because heat rises and pisses my tank off. I've read somewhere that L69 (the HO carburated 305's) were stoped because of the upgraded exhaust boiled the fuel. I am not sure if this is true or not, but it seems like a viable option. Plus 100 degree heat is not good for our pressurized tanks anyways. Not that it should make it reak of gas, but it creates more pressure.

I'll get back to ya with this.
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before I forget.

To check your canister, just unbolt it and flip it upside down or give it a shaking. You should be able to hear "sand like" substance swoshing around. If its not than the canister is full of fuel/saturated with fuel.


Whenever I am at a junk yard I make a habit of snatching one of the canisters off of a car. I check it first than I stash them. Now I have about 10 or so just waiting to work on my car. This might be a good idea for ya just in case you did get it saturated.

 

I replaced the burp valve and drove the car around tonight. NO gas smell. I am pretty sure that with the new valve and exhaust wrapping the muffler the pressure has become a bit more controlable.

I still have to drive it on a hot/hotttt day to see what it does. So far, we are doing great.

 

Drove it today for 2 hours. No gas smells. I can smell the charcoal canister a bit, and I believe that its working again.

So far the new valve, exhaust wrapping the muffler and neighboring exhaust worked good.

My camera needs new batteries and I havent had time to get 'em. Once I do I'll post pics, although its pretty self explanatory.

 

Update.

IT DIDN'T WORK.

Today I was semi hard on it and flying on the highway, next thing you know I park it and wshhhhhhhhhhhhhhhh. I open the fuel filler door and the tank was hot hot. I can feel the heat coming from the fillerneck. I am kinda pissed about this. It makes absolutely no sense. So, I am thinking about cutting the exhaust and routing it some other way with cherry bombs on the end. I've never had a tank that was heating up like that. Even with exhaust wrap it still heated up.

Now, I ask you what else could make the tank hot???

 

UPDATE

Went under the car touching. Sure enough the tank was hot. The heat shield between the muffler and the tank was really hot. Even after I wrapped the muffler.

Than I feel the panhard bar (the one that comes close to the tank) and that thing was hot too. Touched the rear end and WOW it was HOT. It should be hot, but I don't know if it should be this hot.

Anyway, the tank was hot and I think its the exhaust. I'll see if I can shield the tank with anything to keep the heat away from it.

 

I still have the problem too. Though it's better. I went to a shop to discuss moving my muffler forward to just behind the cat using a glass pack or a single chambered. Dang I was hoping your wrapping would solve it so I could do it .
It's $500 to do this using the muffler shops products, they recommended a Magnaflow glass pack. They recommend Magnaflow everything, that's all they sell. If I bring them anything else there is zero warranty. I would then wrap the exhaust tubing all in and around the gas tank. Rear ends do get pretty hot. I can barely touch mine if it has been run a while. That's why NASCAR runs rear end coolers but we shouldn't need it. It's got to be the muffler location and our really hot days combined.

Still wondering if I want to change the exhaust, I don't want an extremely loud car. My 18 year old drives it, it's really his. If he has friends in it with him about a quarter of the time the local cops pull him over for stupid reasons. I'm worried about making excessive noise another excuse for cops to bother him. You know he and his friends got pulled over the other day just because the cop wanted to see if any of them are on probation. They weren't speeding, nothing. These are A and B students with no history of trouble at all. That's why I got him an IROC for graduation. He's responsible, sorry I guess this could be considered hijacking, ranting because he got pulled over again in it to see if he and his friends had their belts on. He driving the suburban now because it makes him nervous to drive it.