|06-04-2015 09:42 PM|
Gonna check that pretty quick......................don't think it has been many years ago but I cannot say when other than that. When in doubt, test, and test again.............hitting 92 or 93 this w/e in temps.
The system does have to hold pressure but I assumed the test was for not for such since looking here lately I have found nothing that says a specific test for it. May have just not tripped over it though. What I have found validates the vacuum idea and I always as well wondered about the pressure test as in, if the PCM wants to do one, just how does it artificially raise the pressure in the tank? I always had an issue with that before, just didn't pursue it out. Stupid me never thought about how easy it is to raise vacuum, simply close off system and let the fuel pump do it.
On an aside, made a smoke machine for the inevitable day, worked fine but the oil worked its' way into the heating element to burn and short it out, mods for that coming up.
|06-04-2015 03:43 PM|
Seems like ORVR handles most/all refuel vapors very well and is only stressed or maxed out during diurnal (siiting) periods.
|06-04-2015 11:21 AM|
|sailor||"Going in that direction" could show another reason for the capless fill system on the MkIII version, with tight fit to the nozzle. That one DOES have a vent to ground between the outside of the cap & the inner seal, proven when it drips with top up attempts. A way to prevent liquid fuel coming out the fill hole when that happens.|
|06-04-2015 04:03 AM|
What's the second reason?
'No it is not...'
My response there was in relation to the operation there too simply described as both ends open with no control there, THAT would be a vacuum leak.....
Crow eating time for me.
Ever since they have put electrical solenoid valves on the canister itself I have assumed they had to be closed and that is WRONG. I wondered if they were open then just WHY did they add the solenoid as it then does nothing??? That all was based on a further assumption (mistake) that the PCM evap system leak test was based on pressure and now I've found it is based on VACUUM which changes everything. The solenoid would then be normally open instead of closed. It only gets closed when PCM commands it for system leak testing, and open the rest of the time.
Look below the first pic to the 'evap canister purge valve no flow test' and the procedure there. That is a VACUUM test...........the PCM also does it on the fly.
My bad and I apologize to all, and thanks to Marde for pushing me far enough to dig further on the subject. My understanding expanded as well.
Still, I view most of the vapor at gas fillup as traveling up that vent pipe rather than going through the canister, the vent has less resistance than canister and much of the vapor is made while sluicing down the filler tube. As long as the bottom of tube door is emitting fuel into the tank it will be emitting vapors out as well, the pressure differential there. Like said before you can visibly see the vapor pouring out of the filler area and onto the ground, getting rid of the gas station vacuum requirement actually will be increasing HC emissions unless the newer systems actually becomes so good they can pass air through canister as fast as that vent pipe. They should be DROPPING the vent pipe on later models and making the filler tube fit the gas pump nozzle tighter, that will stop that and force ALL vapors to go to the canister. Sounds like they are going in that direction...........
|06-03-2015 04:21 PM|
Also, on a similar note, the PCM commands the Canister Vent Solenoid to close during; "seals the EVAP system for the Inspection and Maintenance (I/M 240) test and OBDII leak and pressure tests."
"OBDII leak and pressure tests" are the automatic tests being done by the PCM for Evap Monitor and ditto for PCM checking for evap gross leaks.
As previously stated/guessed, I believe my PZEV has additional controls that would prevent the canister from breathing-to-atmosphere when parked. Also, remember that there other control valves discussed little or not at all during this thread. Ref pic I posted on page-2. I might later go see if I can find a functional diagram and a How-Does-It-Work on the Focus PZEV system.
|06-03-2015 08:21 AM|
The service manual emphasizes several times that it is very easy to break the vent solenoid.
That pic and description are overly simplified, the operation as described would be a running vacuum leak.
Now after looking I'm even getting confused, the ORVR diagrams I'm finding show the canister VENT solenoid as normally open and why do you need a solenoid if the thing stays open?? Easier to be an emission leak that way too. Also, the ORVR diagram shown in the '02 Focus wagon service manual clearly shows pieces of equipment in the ORVR system that my car does not have. It does not show the filler vent pipe either.
'...charcoal absorbs some of the HCs.'
It better be absorbing a lot more than just 'some'. They failed cars here for 20 PPM and so small an amount as to be zero.
|06-03-2015 07:43 AM|
I believe this picture is a good representation of how it works.
When fueling, the gasses go through the canister and out the open vent. As the gasses pass through, the charcoal absorbs some of the HCs. When the car is running, the engine pulls a vacuum, drawing outside air through the canister. The hydrocarbons are released and get burned in the engine. My guess is that charcoal particles make it into the valve, eventually clogging it. I had an old dodge pick up with a slant six where I had to occasionally take apart the 1 bbl carb and clean out the charcoal that got sucked in from the canister which was under the hood.
I see the valve mounted on the end of the canister. Can someone explain how I can release the clips to remove it without breaking them? Looks like that is an issue.
|06-03-2015 07:36 AM|
Pressure differential and resultant equalization will make gaseous matter move around in even a 100% sealed container.............when it heats up or cools down the vapors move. Like said they or fuel cap can open under vacuum so cooling down can flow air one way there.
'Also, if the vapors do travel into the canister during refuel, where is the vapor/air-flow going during this process if it is NOT exposed to an environmental vent?'
I do not acknowledge that really, most of it goes out the filler neck, you can see it easily. At least on the older models. I do not see how the canister even if clogged can make a problem with that relatively huge vent pipe running beside the filler tube. If open it is a much easier and freer flowing vent to depressurize the filling process. The canister being full of charcoal has more resistance. Now if the car does not HAVE that extra pipe a problem there. Even so they will try to vent out of the filler pipe itself, the gas pump nozzle does not seal that off to backward flow. The problem is fully developed when the fuel going in is enough volume and sprayed in to not allow air to work its' way around the incoming fuel. You can often simply move the 'clock' of the gas nozzle around to find a position that even works then, just no one has the patience to think about that. If you stream the fuel in just right it clings to wall of filler pipe and allows a pretty good amount of room for air to bypass it going the other way.
Aquarium charcoal is activated charcoal. Some early '70s Ford charcoal canisters WERE quite literally sealed coffee cans with charcoal inside them. I took AMC plastic ones and yanked the old charcoal and recharged the can and used them for years. The air vent filter was changed for open cell foam and worked fine. You CAN clean charcoal and reactivate it afterwards by heating it to force out anything in the pores of it and then reuse it as well. Simple but don't expect to be told, they would much rather sell you the $100 canister.
|06-03-2015 04:13 AM|
Let's just forget the details of how the ORVR system works, how effective the system works, and move onto finding the guys that wrote that document and getting them to fess-up;
H. Lynn Dail, Environmental Scientist
State and Local Programs Group
Air Quality Policy Division
Glenn W. Passavant, Senior Mechanical Environmental Engineer
Assessment and Standards Division
Office of Transportation and Air Quality
U. S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
Before I go... The OP (and future viewers) had a symptom that resulted in a fueling shut-off condition. Any chance at all this was caused by a clogged canister or a vent valve/solenoid being stuck? Also, if the vapors do travel into the canister during refuel, where is the vapor/air-flow going during this process if it is NOT exposed to an environmental vent?
|06-03-2015 01:52 AM|
They have turned around to put the vent back in the canister where it was gone before. They may have started ORVR in '97 but no way did they use the bigger canisters then, I don't have it in '02. It takes a LOT of charcoal to cover day in/day out emissions from sitting, tried to tell you. I can see rebuild kits for the canisters coming up, you can use simple aquarium filter charcoal for it all day long. BTDT. Cheap. Reckon that bigger canister will cost $300 at Ford?
Note the mentioning of previous charcoal canisters being way too small......Whad I tellya? Look at how much fuel evaps to clog the canister. That partial glassful is enough to do it with small ones. I also doubt highly the current 75% number of cars on the road equipped with the system in 2012; faultily counting only new cars probably. The EPA, LOL.
One day is all the earlier canisters held worth of fuel vapor.
I have not seen any canisters that big yet but that means nothing, I know mine are no way big enough. The explanation is there about how they must get MUCH bigger. The supply hose HAD to be bigger as well, it was a restriction on the smaller units and no way can handle a fillup at speed. Note there is also a new check valve at bottom of main filler tube to stick shut now too. One more thing to make them not fill up right. They will probably be dropping the vent hose to filler neck. There will still be emissions at fillup since the very act of fuel sluicing down the filler tube before the check valve aerates it to separate some HC, some WILL backflow out the filler pipe during fillup. I see nothing that replaces the station vacuum suck at fill neck there. The vapor pathway to and through the canister will have to be a 6 lane freeway to stop that.
And NO WAY will I be calling the air that comes out of the canister 'purified' like the vid does. That seems to say you can breathe it. Too many people will constantly try to overfill the systems when gas prices drop and then mess the canisters up. No way to account for the human effect like always. Of course, the check valve at bottom of filler pipe if sprung right will close to stop overfilling since once fuel is behind it it will cease coming open from fuel weight alone. That stackup and backsplash alone would be a hazardous spill.
Change........it never stops.
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