awesome thread, lots of good technical info. I'm just starting out with this problem, and I'm a HD mechanic, not auto so I don't know anything about EVAP systems lol..... wondering if anybody has an actual picture/diagram with call outs or numbers that shows all these parts of the fuel and EVAP system? I'm following along the trouble shooting, but visually I don't where each of the components are, or which is which under there. I have a 2003 elantra GT..... anybody have a diagram that would pertain to that car?

 

The vapor system traps gasoline vapors in charcoal, rather than venting it as with cars about 50 years ago and more. The system allows air to be pulled through the charcoal to remove the vapors, and take them to the intake manifold. When you shut the engine off, a small blower puts some pressure in the system to check for leaks in the vapor system. The computer measures the current of the blower to do this. If there is no leak, the current is LOW, if the current is HIGH, there is a leak, and the blower is pumping air. Some problems: the charcoal canister has a foam membrane that can dissolve in liquid gasoline. The charcoal granules get pulled into the system clogging it, which can trigger the check engine light. When it is clogged, it is difficult to fill the tank. Another problem is there is an air filter to let air in and out of the system. It can get clogged with dirt, making it difficult to fill the tank (this was the main problem with my Accent). The liquid separator can get clogged with liquid, not allowing the system to vent.


The DM-TL is the electric blower. Air filter was clogged on mine, and the big box holds the charcoal granules.

 

Here is the hose and electrical diagram.


M is the blower. ECM is the Engine Control Module (computer).

 

Here is the entire system. If Hyundai had not used a foam separator in the canister, most of the problems would be solved because charcoal granules would be held in place. They are about the size of Kitty Litter. If they would have just rotated the canister 90 degrees so the ports point up, the problem would have been solved. They are over $700 at the dealers, HOWEVER there are 3 different brands available at Rockauto.com for $111 to $179 for your car. A lot of people cut the top off with a saw, and put something in its place like felt. A mechanic suggested inserting small gas filters in the lines. The filter is designed completely backwards. There are pieces of filter paper in a plastic box, and the smallest ones are what the fresh air hits first, so they clog quickly. I cut it open and replaced the paper with dacron upholstery padding. I checked, and gasoline does not dissolve it. It is working fine. I also pulled the gas tank to clean the vent line. I should have cut the floor above where the vent line connects to the tank for easy access. The Charcoal canister and everything you see in my first picture is in a black box just forward of the rear bumper an the same side as the gas filler neck. You have to remove a plastic inner fender to get to it, then remove the box. If you have charcoal in the lines, you will have to clean the lines and do something to the charcoal canister. It could also be the filter where the fresh air enters the system. Test the blower and any valves. It will take several cycles of the system to reset the check engine light. You can reset it with a diagnostic tester, but that may cause problems if you need a smog check. I'm having that problem with my Mercury Villager. The solution on the van is a new catalytic converter. Good Luck. If you have any questions, please ask.


Left is the front of the car, and right is back.

 

Just an FYI: I must have pulled 10 charcoal canisters out of cars at Pick Your Part before I found one that did not spill charcoal when I removed the hoses. BTW: What's an HD mechanic?

 

Heavy Duty lol. thanks gary, that gives me a good start. I don't have any check engine lights, and the car runs perfect, just wont take any fuel. Also, which I thought was in-related so I didn't mention before, fuel guage stopped working. I just got the car as a project, replaced head gasket, now engine wise all is good. the car sat for 6 months, so I was just driving it around over a couple weeks to use up the old fuel, fuel guage was working. when it hit low, I went to fuel it up, wont take fuel. so I pulled off some lines, dumped a jerry can full in, guage went up to 1/3. next day, went to drive it again, fuel guage sits at the bottom now. I think in-related myself. I'm gonna drop the tank I think, as I think I need to to access the sending unit anyways. under the rear seat is access to the pump, or is that a sending unit/pump combo?

 

so I think I have two problem, fuel guage and not taking fuel. so far I've pulled the charcoal canister down, separated the air filter. the air filter flows fine, but how freely should air flow through the canister? can force air through, but sure is slow..... as I have two problems, i'm gonna drop the tank, i'm sure I'm going to need to anyways at some point through both these problems

 

sorry, reading that I realize I should make the story a bit clearer. saw this car for sale, little old guy owned from new, only has 89000 kms on it. head gasket went, he parked it, he died, it sat for 6 months. I bought it from the son who knew nothing about it. car is immaculate shape. I replaced head gasket, all is now good. drove it around to use up old fuel, guage was working. went to put fuel in, wouldn't take fuel. then guage quite working, although I know it now has 1/3 tank in it. so I don't know a lot about the history of car, my guess little to no work has ever been needed or done, until head gasket. this thread is full of good diagnostic steps, but under the car I was struggling with the terminology and locations of hoses, valves, blower, motor etc etc...... in the world of heavy equipment/diesel, we don't have to worry about EVAP lol

 

The sender is on the fuel pump housing. From sitting, they can get corroded. With the distance units in km, I'm assuming that you are not in the US, so you may not have an extra problem we have. We deal with 10% alcohol in the gas here. It attracts and holds water, so it corrodes things such as the contacts on the fuel gauge sender. It also can attack plastic and rubber. The fittings on the top of the pump and sender housing was quite brittle and broke, so I bought one at a local salvage yard. BTW the fueling problem and gauge are 2 separate problems. I have an extra canister that I was going to cut open if I needed to. I tried blowing through, and the air flowed easily, and a small shower of charcoal blew out along with it, so that one is bad. If the air filter for the system, next to the carbon canister, is flowing freely, then I'm guessing that the foam separator has deteriorated on yours. This separator is just below the area of the canister where the hose fittings are, if you decide to cut it open. There are 2 baffles just below the hose fittings, and the foam is between the baffles. The canister is assembled from the bottom and the bottom is sealed. I can imagine that all this is quite foreign having worked on diesel systems.

 

yes indeed. lots of things are the same, but lots is WAY different lol...... I pulled the tank down, as I just couldn't make sense of the lines up in there, and very poor access. of course I broke a couple crappy plastic fittings etc etc, so I've ordered those. I pulled out the fill vent valve, it appears to be working. the fuel/liquid separator flows air through it fine, all the lines were fine, and the air filter and valve at the filter all flow freelt. I never actually found any charcoal, not even small bits, in any line anywhere. that's what made me doubt the canister. but with the fill vave, lines, separator and filter/valve all flowing freely, the canister is about all that's left, no? it flows through it, I guess just not enough. reading all the comments about charcoal in the lines everywhere when the canister fails made me think that's the only way it can fail, but I guess it can fail/plug without actually letting any charcoal out?

so if i'm going to cut the canister open, I cut it at the end with the hoses, 1" down from the end?