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The canister itself is a passive device; what cause the codes and other issues are either failed valves that control the vapor flow to and from the canister, or blocked lines that prevent the vapor flow, or lines that become disconnected and cause vacuum leaks into the intake system.

The canister is a charcoal filled chamber that absorbs and stores fuel vapor from the tank and then vents it into the intake system to be burned when appropriate. All the rest of the hardware just moves the vapors around.

As for your fuel pump, yes it could be an issue, but can be tested using an appropriate gauge connected to the test port on the fuel rail. Some times these fuel pumps “come adrift” from their mounting inside the fuel tank and cause no end of problems, but are also very difficult to diagnose because the fuel pressure looks normal with the car stationary.

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Old 04-10-2012, 12:14 PM
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Thanks JFP for the codes explanation. What I'm trying to wrap my head around. Is why the vapor canister or associated lines would cause the car to be hard to start when at normal operating temps. And sits for awhile. Are they causing a vapor lock of some sort. Like the old days. Had a VW bug that would do that oddly, enough.
The engine has died in the past while driving (been awhile though), that would indicate the fuel pump possibly. Turd on here just had that problem, because his had come lose from the mounting base.
I really appreciate your time in giving response's to these questions. And all your advice in the past as well as everyone that has helped me with my questions on this site.
When I post issues that I'm having. My hope is to also help others with there problems as well. If they have similar ones with there's. As an X-Admin on an R/C site. That is just the way I think interaction on sites like this should be handled.
Randy
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Old 04-10-2012, 02:00 PM
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The fuel system in the Boxster has no external vents (it is “closed loop”); as such, it is possible for the fuel tank to develop internal pressure or vacuum if the EVAP system is not working correctly, depending upon what the fault is. The car does not like this when it happens, it can run poorly, stall, or refuse to start. The trick is fixing it has always been to make sure the fuel delivery system (pump, etc.) is working correctly, and then find and eliminate the source of the venting problem.

Next time your car won’t start, remove the gas cap, observing if the is pressure or vacuum (either one will “hiss”, so you need to be observant). If the tank is strongly pressurized, it is not venting into the engine through the EVAP control system.
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Old 04-10-2012, 03:23 PM
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JFP. Thanks for the explanation. Makes sense. The next time it won't start will be under one of two conditions. Me trying to get the tank down to a level to remove the fuel pump safely. Or after the new fuel pump I ordered today is installed. But more than likely. Before it's installed. But I'll check that hissing thing. Although I have in the past. But I may have not been listening close enough?

I went with my gut feeling and ordered the fuel pump. I've done that at least twice before. And I'm still married to one of them. Although, she is in a neck and neck race as far as the expense's to keep happy!!!

Randy
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Old 04-10-2012, 05:26 PM
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[QUOTE=JFP in PA;6678513]The canister itself is a passive device; what cause the codes and other issues are either failed valves that control the vapor flow to and from the canister, or blocked lines that prevent the vapor flow, or lines that become disconnected and cause vacuum leaks into the intake system.

The canister is a charcoal filled chamber that absorbs and stores fuel vapor from the tank and then vents it into the intake system to be burned when appropriate. All the rest of the hardware just moves the vapors around.

QUOTE]

So JFP. When it gives us the code.

P0446:
Shutoff valve activated charcoal filter (function) below limit value

Does that mean that the vapor has turned to a liquid or the charcoal filter is clogged to the point it won't operate correctly? I think that is what you mean. Like an air filter that gets clogged full of dirt. Just checking and it may help others on here to understand what it does. Not trying to over think things. Or bug you. But I love knowledge of how things operate and why.
I tend to research the crap out of everything. Well except my first wife.
Hope all is well in PA.
Randy

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Old 04-18-2012, 02:18 PM
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Hmmm, Found this on the wonderful net. Thanks Google.


What is a Carbon Canister?
Carbon Canisters are devices found in automobiles designed to decrease the amount of air pollution the vehicle creates while at the same time increasing its fuel efficiency. Even when the vehicle's engine is turned off, hydrocarbons are produced. This occurs in the form of fuel vapor rising in the fuel tank. Carbon Canisters trap that vapor rather than allow it to escape the fuel tank, feeding it back into the engine.

Structure
Carbon Canisters are rectangular shaped boxes that sit apart from the fuel tank next to the throttle in most vehicles. There is an input port and an output port, with the two ports side by side. There are three chambers inside the canister, running in sequence from the intake to the outtake. The interior of the canister is filled with charcoal or carbon pellets. The input of the canister connects to the gas tank's vent port, while the output connects to the purge valve in the side of the vehicle's intake manifold.

How does a Carbon Canister Work?
When the vehicle is shut off, there is a pressure imbalance within the fuel tank caused by fuel being siphoned out, but no air being let back in to take up the empty space. The lower pressure in the gas tank promotes a greater rate of evaporation, letting some of the fuel become a gas. Eventually the tank's internal pressure equalizes, at which point the gas leaves the tank through the vent port and goes into the carbon canister. It's trapped there by the properties of the carbon within the canister, keeping it from escaping into the air. When the vehicle's engine starts, the sudden suction created along the intake manifold opens up the purge valve and pulls all the gaseous fuel out of the canister and burns it in the engine. The canister goes unused until the car is turned off again.



Read more: How Does a Carbon Canister Work? | eHow.com How Does a Carbon Canister Work? | eHow.com
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Old 04-18-2012, 02:22 PM
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[QUOTE=randy_k;6696166]
Quote:
Originally Posted by JFP in PA View Post
The canister itself is a passive device; what cause the codes and other issues are either failed valves that control the vapor flow to and from the canister, or blocked lines that prevent the vapor flow, or lines that become disconnected and cause vacuum leaks into the intake system.

The canister is a charcoal filled chamber that absorbs and stores fuel vapor from the tank and then vents it into the intake system to be burned when appropriate. All the rest of the hardware just moves the vapors around.

QUOTE]

So JFP. When it gives us the code.

P0446:
Shutoff valve activated charcoal filter (function) below limit value

Does that mean that the vapor has turned to a liquid or the charcoal filter is clogged to the point it won't operate correctly? I think that is what you mean. Like an air filter that gets clogged full of dirt. Just checking and it may help others on here to understand what it does. Not trying to over think things. Or bug you. But I love knowledge of how things operate and why.
I tend to research the crap out of everything. Well except my first wife.
Hope all is well in PA.
Randy

Randy
OK, letís see if we can clear up any confusion.

The EVAP canister is a plastic container full of activated charcoal granules (much like the ones used to clean the water in a fish tank filter). Their purpose is to suck up and trap hydrocarbon vapors from the fuel tank and hold them until the system opens the purge line and sucks them into the intake system to be burnt. This process eliminates any hydrocarbon release from the fuel system to the atmosphere. The EVAP canister does not see liquid fuel; it is a vapor only unit.

The canister shutoff valve closes to seal the purge air line to the EVAP canister while the system is running the fuel tank leak test (a pressure test to verify that the fuel system is totally sealed from the atmosphere). When the system is running the pressure test, if either the purge air line is blocked, the shutoff valve has malfunctioned, or the resistance to airflow in the EVAP canister has become too high (due to contamination or the charcoal breaking down and clogging the passages), the car will throw the P0446 code.

Diagnostic procedure is to check the purge air line and canister purge valve for blockage or malfunction; if blocked, blow it clear or replace it. If the line and valve are OK, the EVAP canister has to be changed out, it is not serviceable.
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Old 04-18-2012, 02:47 PM
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Randy, I think you said you have a Durametric.

For anyone else that knows, I'm curious what's supposed to happen when you click "fuel eveporative valve." Meaning, is there a way Randy can check to see if his valve is opening and closing correctly?

I've activated mine tonight, to see if I could hear a sound, like the clicking that's heard when you activate the IACV. But, nothing. Either that valve is super quiet, or mine's not working either. It should be the valve that's connected to the top of the charcoal canister, right?


Old 04-18-2012, 07:18 PM
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Keith, I believe the connection at the top is what tells the DME that it's over it's below limit value. By looking at it. See pic below.



The 986 PTE shows the purge valve at the manifold. And so does the Bentley manual. But from other things I have read. It's electronically controlled on the other cars I have seen info on. But there are no electric connections on it at the manifold. I can find. So the only thing I can think of. Is when the car sits. There is a vacuum created in the canister that pulls the purge valve closed at the manifold. Which makes since. Since like JFP pointed out. It's a closed system. If the purge valve sticks open. Then the DME sees crap it doesn't like and sends the engine into a tizzy. Which could be caused by the canister not working and releasing pressure in the wrong direction. It won't suck anymore in from the line that goes to the manifold.

Since it seems like the DME on these things makes all the wrong decisions. Or should I say. One's that I don't understand? One more reason to refer to it as she.

The one in the pic is one I found off of a totalled 986 with half the miles on it than mine for $49.00 bucks. At this point. I'm about outa bucks to spend on it. And naturally. After some research. MY 99 can have three different ones. Ranging anywhere from $147.00 to $247.00 Guess which one was on mine???
I'll blow the line clear, (purge line). Put this one on and see what happens after I'll clear the codes.
New fuel pump will be here tomorrow. And down the rocky road I go. Anyone up for a "Diary of a Charcoal Canister" thread

But hey. At least my tires are new.

Are we having fun yet??? Randy
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Old 04-18-2012, 08:04 PM
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Quote:
Originally Posted by bar10dah View Post
Randy, I think you said you have a Durametric.

For anyone else that knows, I'm curious what's supposed to happen when you click "fuel eveporative valve." Meaning, is there a way Randy can check to see if his valve is opening and closing correctly?

I've activated mine tonight, to see if I could hear a sound, like the clicking that's heard when you activate the IACV. But, nothing. Either that valve is super quiet, or mine's not working either. It should be the valve that's connected to the top of the charcoal canister, right?


Keith, I havn't even tried to activate half the things on the Durametric. As I have no idea what good they would do setting still. Engine off.
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Old 04-18-2012, 08:06 PM
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And thanks JFP for your time and education.

Randy
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Old 04-18-2012, 08:09 PM
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Quote:
Originally Posted by randy_k View Post
Keith, I believe the connection at the top is what tells the DME that it's over it's below limit value. By looking at it.
The top connection (red arrow) is what I took off and blew compressed air through several months ago, which appeared to clear my P0446 code. From post 13 in this thread, it appears to be the line marked #3 in that diagram.

The electrical connection underneath that (blue arrow) is what I think is the purge air valve, and marked #6 in that diagram. Anyone know of a way to test it? Since I had my right front fender liner out today to replace my radiator fan resistor, I activated the "fuel evaporative valve" in Durametric, but this valve didn't make any noise. Either it's super quiet, or it's broken.



Since I had Durametric out, checked for pending codes, sure enough, I had P0446 again! So, I blew compressed air through that upper line again. I also removed the connection at the bottom of the charcoal canister (the one towards the front of the car, appears to be ) and blew compressed air through that one. When I removed the air tool, I could hear air rushing back out. So I blew air through again, then when I removed the air tool, I put my finger over the opening in the line. Appears the air I blew into the line built up within the line and blew back out. Like, the line had inhaled and then exhaled. Is that normal for that line?

Let me know if I'm wrong here. I'll update as corrections need to be made. I'm basing all this on the not so clear diagram (it's hard to trace those lines!) and the explanations from JPF in this thread. Appears vapors from the fuel tank enter the EVAP system through the red lines, through #5 the pressure sensor and travel to the bottom rearmost connection of the charcoal canister. Then the vapors leave the canister through the bottom frontmost connection and travel up to the filler neck colored green, passing through #9 the vacuum control valve, and onto #7 the operating purge valve. From there the vapors follow the route of the gray line, into #1 the purge valve, and ultimately to #8 the intake manifold, where the vapors get burned in the normal combustion cycle. #3 purge air, appears to just be a vent for the charcoal canister?



So Randy, guess I'm back in the same boat as you. Gotta figure out why we're getting these P0446 codes...
Old 04-22-2012, 05:38 PM
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Kieth. Well I put a new fuel pump on it yesterday and that used charcoal canister. Canister was a mistake. But oh well. Should have waited and bought a new one. In any case, it's as bad as it was if not worse. When I get it up to normal operating temps and turn it off. It doesn't want to start. Right after or 45 minutes after. After hitting the starter and throttling it, feathering the throttle, catching it before it dies a few times. I can get it started. And once I do. It idles just fine and all is good. So, I'm done throwing money at it for now. I don't have anymore to waste on it. Going to put the old canister back on and check the CPS to see if it looks like it did 15 months ago. If it does? Then there's a chance it's the flywheel messing it up. If that's the case. I GIVE!!! It just really irritates me (I have a little stronger language I'd like to use. But out of respect for Wayne's site, I won't) that I had finally got all the gremlins fixed on it and it had run great since last September. And now. It's a hunk of lead with Porsche emblems on it.
Let me know though what you come up with.
Randy
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Old 04-23-2012, 02:21 PM
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Quote:
Originally Posted by bar10dah View Post

So Randy, guess I'm back in the same boat as you. Gotta figure out why we're getting these P0446 codes...
Keith, Did you ever gt that code to clear? (P0446)

Randy
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Old 04-28-2012, 09:48 AM
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I cleared it last weekend, after having blown out the lines. I haven't checked since. It hasn't set a CEL. But, it hadn't set it last weekend either, as it was a pending code. I'll check again this weekend and let you know.

I'm still getting P1124 and P1126, so I wonder if P0446 is linked to my other codes.
Old 04-28-2012, 10:54 AM
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Thanks Keith. I made the mistake of not clearing my codes before I test drove it last weekend. So not much point in checking them again at this point. I haven't touched or started it, since I pulled it back in the garage last Saturday either. Busy working and just haven't felt like it. Maybe next weekend??? Or not. I may just wait until I can order a new Charcoal canister and the line with the purge valve in it.
I also have a Honda lawn mower that has decided to be a Porsche. That needs my attention. Good news is. The parts are cheaper for that.
Let me know what you come up with.
Randy
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Old 04-28-2012, 12:04 PM
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Yep, P0446 came back. Blowing compressed air in the lines didn't help.
Old 04-29-2012, 11:14 AM
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Originally Posted by bar10dah View Post
Yep, P0446 came back. Blowing compressed air in the lines didn't help.
Bummer. Like I said. A new canister and line with purge valve are in my future. At that point. I'll have spent all the money it would have taken to buy the paint and supplies I need to repaint the car.

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Old 04-29-2012, 11:20 AM
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Well, went to start it today just to get the door stop out of the shop. It started up pretty quickly ran for about 10 seconds and died and refused to restart. I let it sit for 8 hours and tried to start it and no joy. As Maverick in Top Gun would say. So I'm guessing. (What isn't on these things.) I have something in the fuel tank screwed up from when I changed out the fuel pump. I smell no fuel at all. I'd do a fuel pressure test. But I think I have to have some sort of trickle to the manifold to even get an idea.
I doubt if the purge valve or canister would shut this thing down completely.
So for another few days. I'll push it up to the door to the shop and use it for what it is best suited for now. Keeping the door in a static position. Because the car isn't going anywhere. That's for sure.

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Old 05-04-2012, 06:20 PM
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Also got these codes. Which I know most are meaningless

Bosch Digital Motor Electronics Motronic 5.2.2
Module Identification



Part Number 986.618.621.01
Supplier Part Number 004155073601


Current Fault Codes

P1602:
Supply voltage Open circuit


P0134:
O2 sensor ahead of cat. conv. Cylinder (1-3)


P0154:
O2 sensor ahead of cat. conv. Cylinder (4-6)


P0102:
Mass air flow sensor short circuit/open circuit



The first is because the battery was outa the car. Seen that before as well as the airflow sensor. That's because of the bad running when it did start last time. And the O2 sensors as they are BOTH brand new.
When it gives me a code that reads. DO YOU OWN A SHOTGUN? Then I'll know it's serious about the codes!!!

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Old 05-04-2012, 06:25 PM
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