i read this on another forum on how to test for leaks in EVAP system . Although i belive the smog machines use nitrogen for safety reasons but why cant i use compressed air like this guy ...............

I want to do this because i failed the smog evap test , and also when i put gas in the pump shuts off every 2 seconds.

Hello fellow Californian. Isn't the new test the pits? My shop reguarly has to run the test two or even three times to get good results. The evap system is a bunch of hoses and your charcoal canister. The system collects vapors so they don't choke us all. The most likely culprit is the vac hose that goes back to your tank from the charcoal canister. However there is a way to troubleshoot this yourself. Since I go through this regularly, I took an old, Stant fuel cap, the kind with the plastic threads that go in the filler neck. I broke off the top leaving just the bottom part of the cap. Drill out the center and tap it for pipe thread. I think mine is 1/4" NPT. I put a hose barb in there and attached a piece of vacuum hose to that. When installed it leaves this hose dangling by the side of the car. I can pressurize the system with my compressor, cap it, then slide underneath and check for leaks. Hoses get old and split. Even charcoal canisters can crack. Vacuum elbows perish, etc.

[This message has been edited by bsculptor (edited 06-13-2008).]

NO!

All you should need is a hand pump. More than a couple PSI and you'll almost certainly damage something. Worse you could spray fuel all over the place. This kind of work needs to be done far away from anything that makes sparks.

Also... exactly how was the test done...

Fiero must have the vent line to the canister clamped when this test is done. If that clamp is not applied properly, it won't pass.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top of every forum page...)

To expand on late last night.....

If you use a compressor and a really long hose... A compressor regulator often has a really hard time getting to the low PSI you need. You only need a couple PSI as noted.

Even if you don't spray liquid fuel... you will vent allot of vapor during testing if there is a leak. Fuel vapor can become explosive very easily and with the right weather conditions can do this even outdoors. This has to be done with plenty of ventilation.

For a start, get a new gas cap. Use Stant. The gas cap is a very common fail item on EVAP testing so just eliminate that right away. Save the old one in case you want to make the above adapter.

The fastest test is to disconnect the vent line from the EVAP canister. Its the big line. Get your hands on a hand or foot pump and valve stem. You can cut the stem from an old inner tube or trim down one from a car tire to fit in the line. Clamp the stem in and connect the hand pump.

If you get a pump with a gauge that screws in this will be allot easier. (Many foot pumps are like this.) Replace the original gauge with one that only reads 5-10 PSI max. (You may need some adapters to do that.) See if the tank will take 2-3 PSI, not more than 4-5 PSI, and hold it when connected as I just described. If it holds, then the EVAP test was probably performed incorrectly or the gas cap was what failed. (Here in DE they tell you if it was the cap or tank. They're tested separately. Some places maybe don't list them separately or don't test the cap...)

If it does leak down... Just in case the check valve in your pump leaks... clamp the line on the pump after inflating the tank. If the check valve leaks, no uncommon, the gauge reading should drop right off. Leave the line clamped and let the system stand 10-15 minutes. Unclamp the line and take a reading. It should be the same as when you clamped the line.

Also... watch out for temperature. If the tank temperature changes very much then it could skew your readings. It shouldn't change very much in a few minutes but if you've pulled into a a hot driveway or just driven, it could be something to cause you a headache. This is best done with the car "cold."

The EVAP canister body CANNOT be tested for leaks on the car. There is nothing stopping air/vapor movement thru it beyond the charcoal inside. If the case has cracked it is usually not hard to find. The canister valve can be tested on the car but if that is bad you usually also have the symptoms of a vacuum leak. (I think there are more notes on this in my cave.)

All Fiero should pass a properly preformed EVAP pressure test on the tank. Both tank designs are sealed and should be venting only thru the canister.

Performing it correctly usually isn't very difficult. If they fail to properly clamp the vent line, use the wrong test adapter, or don't get a good seal on the test adapter then it can be rather annoying. In DE I can watch them do the test, which makes it fairly easy to see when there is a problem. I also remove the vent grate for very easy access to the canister. (I replaced the screws with the wing type used on the right grate just for this reason.) The clamp they should be using is long enough to reach under the grate but removing it pretty much eliminates any chance for error. (It can be a little awkward to reach even with the long clamp.)

[This message has been edited by theogre (edited 06-14-2008).]

quote Originally posted by theogre: To expand on late last night..... If you use a compressor and a really long hose... A compressor regulator often has a really hard time getting to the low PSI you need. You only need a couple PSI as noted. Even if you don't spray liquid fuel... you will vent allot of vapor during testing if there is a leak. Fuel vapor can become explosive very easily and with the right weather conditions can do this even outdoors. This has to be done with plenty of ventilation. For a start, get a new gas cap. Use Stant. The gas cap is a very common fail item on EVAP testing so just eliminate that right away. Save the old one in case you want to make the above adapter. The fastest test is to disconnect the vent line from the EVAP canister. Its the big line. Get your hands on a hand or foot pump and valve stem. You can cut the stem from an old inner tube or trim down one from a car tire to fit in the line. Clamp the stem in and connect the hand pump. If you get a pump with a gauge that screws in this will be allot easier. (Many foot pumps are like this.) Replace the original gauge with one that only reads 5-10 PSI max. (You may need some adapters to do that.) See if the tank will take 2-3 PSI, not more than 4-5 PSI, and hold it when connected as I just described. If it holds, then the EVAP test was probably performed incorrectly or the gas cap was what failed. (Here in DE they tell you if it was the cap or tank. They're tested separately. Some places maybe don't list them separately or don't test the cap...) If it does leak down... Just in case the check valve in your pump leaks... clamp the line on the pump after inflating the tank. If the check valve leaks, no uncommon, the gauge reading should drop right off. Leave the line clamped and let the system stand 10-15 minutes. Unclamp the line and take a reading. It should be the same as when you clamped the line. Also... watch out for temperature. If the tank temperature changes very much then it could skew your readings. It shouldn't change very much in a few minutes but if you've pulled into a a hot driveway or just driven, it could be something to cause you a headache. This is best done with the car "cold." The EVAP canister body CANNOT be tested for leaks on the car. There is nothing stopping air/vapor movement thru it beyond the charcoal inside. If the case has cracked it is usually not hard to find. The canister valve can be tested on the car but if that is bad you usually also have the symptoms of a vacuum leak. (I think there are more notes on this in my cave.) All Fiero should pass a properly preformed EVAP pressure test on the tank. Both tank designs are sealed and should be venting only thru the canister. Performing it correctly usually isn't very difficult. If they fail to properly clamp the vent line, use the wrong test adapter, or don't get a good seal on the test adapter then it can be rather annoying. In DE I can watch them do the test, which makes it fairly easy to see when there is a problem. I also remove the vent grate for very easy access to the canister. (I replaced the screws with the wing type used on the right grate just for this reason.) The clamp they should be using is long enough to reach under the grate but removing it pretty much eliminates any chance for error. (It can be a little awkward to reach even with the long clamp.)

Thanks for your info, it will be a great help. This is my whole story ,

I went to the smog test , everything went fine . Until i get to the Evap test. The pressure line he uses goes through my filler pipe , so my gas cap is not even used during the test.
Once he started , There was gas leaking from what it looked like around the filler pipe/vent tube. I backed up the car and it stopped . (I have never seen gas leak on my car until he put the pressure from evap test.
We stopped the test and went next door and looked under the car , but we could not see where it was coming from. (gas evaporated pretty quick)
So we tried it again , and it failed the test . (no gas came out this time)
But before i even went to get my car smogged , i noticed everytime i went to fill up the tank , the pump clicks off as if the tank was full. every 2 seconds it did this . (takes me forever to even get a half a tank)

So i am thinking there is a few problems .
I replaced the evap canister and put in some new tubes.
I am going to replace the filler pipe and vent tube.
After this i am going to go try and fill up on gas to see if it changed anything . if not , i am going to do what you suggest .

Thanks for not letting me blow up myself with my air compressor and gas !

Yikes! Stop Driving It!

The EVAP canister won't cause you problems filling the tank. Tank Fill problems are often blocked/pinched hose(s) that runs from the tank to the fill door. You could have trash in the tank but usually it's a line problem. (This assumes that it happens at multiple stations/pumps. It's not uncommon for the problem to be the fill nozzle if it only happens occasionally.)

As I remember... Haven't looked in awhile... There are 5 hoses on the tank.

1. Fuel Fill
2. Fill Vent
3. Fuel Out
4. Fuel Return
5. EVAP Vent

# 1 & 2 are on the back of the tank proper. The others are on the fuel pump assembly.

If you blew fuel during the test... I would guess you've got a pretty full tank. You could have a rot hole in the tank or the lines.

Problem is that if you blew fuel during a minor test... you're probably also blowing fuel while driving. You really need to fix this before driving the car any or you could easily find yourself a rolling fireball. Fuel leaks near hot exhaust is a sure recipe for disaster.

Hello Fellow Californian!
Yeah,...I failed too but we found that the metal tube from the fuel tank to the canister was cracked, Of course, this was discovered after REMOVING THE TANK (and then, while you're there, replaced the fuel pump components).
Hey,.....shi* happens!
Remember, these cars are dated and things crack, rot, and eventually break.
I still love my car,.........anybody want to buy it??