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Griffter
Monza


Joined: 22 May 2016
Posts: 236



PostPosted: Sat Oct 13, 2018 8:44 am    Post subject: Reply with quote

Blimey. I assume the tank is plastic, not metal?
 
  
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maldren
Österreich


Joined: 07 Oct 2016
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PostPosted: Sat Oct 13, 2018 8:52 am    Post subject: Reply with quote

My guess is galvanised steel, sheet steel collapses easily with a vacuum.
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2003 996.2 C2 Coupe Arctic Silver
 
  
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infrasilver
Fast & Furious
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Joined: 04 Oct 2010
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2001 Porsche 996 Targa

PostPosted: Sat Oct 13, 2018 11:30 am    Post subject: Reply with quote

It is some dense plastic material, I have thought about trying fo reshape it with either with compressed air or another way I heard of, filling with boiling water and knocking it back to shape with a wooden drift. I have another tank to fit anyway so will see if it goes back to shape once the car is back together just as it may help someone else make the decision, to buy a new one or repair.
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infrasilver
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PostPosted: Sun Oct 14, 2018 1:10 pm    Post subject: Reply with quote

A picture for comparison before I fit the new tank.


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infrasilver
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PostPosted: Thu Oct 18, 2018 10:22 pm    Post subject: Reply with quote

So with what seems like a good few hours over a few days I have eventually replaced the fuel tank and fitted the new fuel filler vent valve (Bleeder) and all other parts required. It was a bigger job than expected with having to remove the coolant and pipes and also drop the subframe. I'm currently at the stage of putting all the coolant back in the system and I have also now traced this elusive vent pipe from the top of the carbon canister at last.



It runs under the car with the purge valve pipe and the fuel feed pipe.



Where the other two pipes carry on to the engine this pipe ends above the gearbox mount and is mounted to the underside of the chassis and is vented to atmosphere, so the system isn't as fully sealed as thought.

I still need to blow air through this pipe to make sure it is not blocked.



The issue is though, how is this system replacing the fuel in the tank that's been used with air to stop any vacuum issues again? It should work fine as this is how it comes from the factory?

I have everything new, as new and tested but the one way check valve (pictured below) that runs from the fuel filler vent valve to the bottom of the carbon canister is the thing that I can't work out.



With it being a check valve it only flows one way (down) and that is to let air out of the tank when filling up, this does not let any air into the tank. As this check valve is between the carbon canister and tank the pipe that vents to atmosphere can't bring air back to the tank due to this valve being tank vent only?

So I have today removed the working check valve and pipe and replaced it with one that doesn't work properly ie the diaphragm is broken (allows air either way) and hopefully this will allow air to pass freely when the fuel cap is fitted, in turn opening the fuel filler vent valve? This should take air back through the carbon canister from the newly discovered vent pipe. Although this way the tank doesn't pressurise and may cause altitude issues again?

Its all hard to explain unless you have seen what goes where so I have amended my original diagram to show how the system is although the check valve is allowing air both directions instead of just out.


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alex yates
Brands Hatch
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Joined: 06 Mar 2014
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Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Thu Oct 18, 2018 11:03 pm    Post subject: Reply with quote

alex yates wrote:
I'd check how much it takes to fill it. Could have an imploding fuel tank.


Wink
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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5723
Location: Brighton


PostPosted: Fri Jan 04, 2019 7:03 pm    Post subject: Reply with quote

Had a chat with the guys at work today and we think we have got our heads around how this system works ...

The open vent pipe you found would be to vent any excess vapors but mainly to be a breather for the carbon canister ... in other words you cant get something into a canister unless air can come out .

This pipe will NOT stop the tank from collapsing .

The pipe with the valve / damper on it ...

The damper is probably pressure related and is there to stop vapours entering the entire line upto the engine , if this blocks and resticts tank venting then the petrol tank Will collapse .. we have seen it before.

This pipe basically runs upto the purge valve on the engine and its this part of the system that stops tank collapse .

When the ignition is first switched on it opens the purge valve there by venting the fuel tank and allowing fresh air into the carbon canister .

Engine started and the purge valve is closed and stays this way until the engine is at temp .. this will create a vacumn in the fuel tank and we guess help the carbon canister suck up the vapour .

The tank vent occurs for about 300 seconds then switches off for 100 seconds .. in the off position the car will adapt fuel trims etc for the best running of the engine ( car adapts to worn or knackered components ).

Every time it tank vents then it will release any vacumn in the fuel tank.


Soo .. as this pipe is the only way to stop a tank collapse then it must be the problem ..

The pipe with the valve being the main culprit .

After that its the pipe to the engine and the purge valve itself.

My thinking on this .. if the pipe has been replaced then we are left with the purge valve .. this has also been replaced so we are left with the pipe from the canister to the engine ..

Be it partially blocked ( crushed ) or an internal blockage ... it wont allow the volume of air through the tank needs to stop a large vacumn build up over time .

The only other possible cause is the dme .. if it doesnt open the purge valve when it should then the tank will collapse.


Phew ! got there in the end.
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Chris_in_the_UK
Estoril


Joined: 19 Mar 2014
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PostPosted: Fri Jan 04, 2019 8:12 pm    Post subject: Reply with quote

^^^^^

Which might be the 'hesitation' problem Chris is experiencing?
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deMort
Zolder


Joined: 21 Mar 2015
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PostPosted: Fri Jan 04, 2019 8:19 pm    Post subject: Reply with quote

He has " modified " this valve / damper .. which seems to be causeing the car to run lean .. im not sure if the purge valve is functioning correctly as it shouldnt do this but im afraid im guessing .. i have the car in front of me when i work on them normally .. on here its just an educated guess and if its an unusual problem then i cant really help .

I think swopping the fuel pump back to the original one is a good start for that hesitation fault .. although it could be conicidence and something else has failed.

Its a difficult one and something i can only give advise on but to be honest i would need a lot more info ( tester values ) and probably have to have the car for a while to fix it .
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Locosaki
Spa-Francorchamps


Joined: 03 Jul 2016
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PostPosted: Fri Jan 04, 2019 8:45 pm    Post subject: Reply with quote

With mine when I had the faulty purge valve I’d drive for around an hour or so then I’d get a buzzing from the fuel cap area I also found the car would crank over without starting, it took a while for me to work this out but I eventually realised if I opened the fuel cap the car would start no problem.

My car did throw up a fault for evap system though, I worked my way through things checking evap pipework for blockages with compressed air, lastly I removed the purge valve and put power to it and nothing happened and it was open circuit with the multi meter if I remember correctly, I sourced a used one (wasn’t Porsche valve) put power to it and it clicked open where the old one didn’t, fitted this to car and no more faults for the evap system and the buzzing and sluggish starting are done with now too.
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Griffter
Monza


Joined: 22 May 2016
Posts: 236



PostPosted: Sat Jan 05, 2019 10:09 am    Post subject: Reply with quote

deMort, not to contradict you but rather to try to add to your post, I thought the carbon canister was to filter vapour venting to atmosphere rather than air entering the tank?
For example when the tank is half empty, on a hot day the vapour will expand and increase the pressure in the tank. The vent valve and canister allow the vapour to vent to atmosphere but the carbon reduces the HC in the vented vapour.
Perhaps the vent/canister works in both directions?
Or I may be wrong!
 
  
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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5723
Location: Brighton


PostPosted: Sat Jan 05, 2019 5:01 pm    Post subject: Reply with quote

Griffter you are more than welcome to contradict me any time you want Smile i certainly dont know everything .. all i can ever do is give my opinion the same as everyone else .

i dont know the system 100 % but have figured most of it out and to be honest i was trying to bump this thread and get a few more comments so that perhaps we can figure out whats causeing the tank collapse .. Infrasilver has modified a pipe atm ...

So in my eyes we still havent got to the bottom of this .. and i would like to .

The carbon canister is indeed there to catch fuel vapours .. one for save the planet but mainly its a dam waste of a burnable fuel to just dump it.

Its just a canister with activated carbon granules as far as im aware .. fuel vapour will be collected in these granuals and when needed be drawn into the engine.

The part i was struggleing with is that dam pipe thats open to atmosphere .. you would think that this pipe would stop a tank collapse but the diaphram pipe had been replaced and thats the only part i can see that would block ANY air getting into the tank other than removeing the filler cap ...

yet it still collapsed .. this and Locosaki post above yours .. his was similar and the vent valve on the engine was causeing it makes me think that although this pipe is open perhaps it cant give the volumn of air to the tank that is needed .

As fuel is pumped out of the tank then air has to replace it from somewhere .

It may be a combination of this pipe and the valve on the engine that does it .. either way those are the bits that need checking .. we dont have a blockage but a restriction i feel .

Couple of images .. one is the american system but that is different to ours .. we have no pressure sensor or shut off valve ..

The other is the canister internals .. again we have no shut off valve there.
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infrasilver
Fast & Furious
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Joined: 04 Oct 2010
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2001 Porsche 996 Targa

PostPosted: Sat Jan 05, 2019 5:50 pm    Post subject: Reply with quote

Sorry for the slow response the last couple of days, we have had pet death at home so I haven't been in the garage at all to even look at the hesitancy or this EVAP system again.

The thing we really need to establish is how air gets back into the tank and there are only two ways it can as far as I'm aware, the first being the tank vent pipe running from the bleeder valve on the filler tube to the bottom of the canister and the filler pipe bleeder valve itself. The vent valve is one way only so cannot get air into the tank, only take air away, like when you are filling the tank with fuel. The bleeder valve can be the only other way?

The purge valve at the engine again only takes fuel vapour from the tank/carbon canister to burn. Anything past the carbon canister cannot return air back to the tank due to the factory vent valve.

This is why I'm using an old pipe where the diaphragm has broken, allowing air to pass both ways, just to relieve the vacuum when the tank is getting empty. This should let air back into the tank through the carbon canister from the pipe open to atmosphere that exits under the gearbox. I'm still not sure what part the open pipe plays in this system, its just an open pipe from the top of the carbon canister??

Its all not correct and how it was designed but seems to be holding the tank together but won't get it thorough an MOT, I just swap the pipe over at MOT time as I did a few weeks ago.

But as you do deMort, I would like to fathom out what the problem is.
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infrasilver
Fast & Furious
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PostPosted: Sat Jan 05, 2019 5:52 pm    Post subject: Reply with quote

Just to add, I do have an old carbon canister, I will cut it open at my next opportunity and take a pic.
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deMort
Zolder


Joined: 21 Mar 2015
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PostPosted: Sat Jan 05, 2019 8:30 pm    Post subject: Reply with quote

Chris .. i am truly sorry for your loss .. it is heart breaking .

Ill not continue this until you have moved on .

I have a theory but it goes against what you think so its best if we give it a bit of time untill you are ready .

Once again .. i am truly sorry .
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infrasilver
Fast & Furious
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Joined: 04 Oct 2010
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2001 Porsche 996 Targa

PostPosted: Sat Jan 05, 2019 8:54 pm    Post subject: Reply with quote

It is a sad loss but he had 15 great years but I'm also happy to crack on with this. These things happen as most of us know but it's also good to keep the mind busy.
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alex yates
Brands Hatch
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Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Sat Jan 05, 2019 10:53 pm    Post subject: Reply with quote

My condolences Chris, dreading the day I lose my 4 legged best mate.


On a side note, I reckon it's deffo a fuel delivery issue.
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deMort
Zolder


Joined: 21 Mar 2015
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PostPosted: Sun Jan 06, 2019 7:18 pm    Post subject: Reply with quote

Fair enough young man.

Imho you have several faults atm , when you get the durametric hooked up then i can try and work through things with you .

For now the tank fault ..

Image below that i have edited ..

My opinion .. No.7 is called a Vacuum limiting valve .. so thats what it does .. i dont feel its a one way valve but i think its a vacuum valve that opens when there is excessive vacuum build up in the tank .. this will then allow air to enter ther tank either from the canister pipe that vents to atmosphere or the engine purge valve .. or perhaps even both .

Also think of just how much vacuum it would take to colapse a fuel tank .. that plastic is harder than steel .. its designed to withstand a serious car crash .

There are no other pipes on the tank or filler tube .. so the diagram we have is it .

There is nothing in the fuel filler cap that has a vent , its not like a coolant cap which can release with pressure as far as im aware anyways ... the cap seals the filler tube .

If it was me .. i would replace no.7 with a brand new pipe , i would check that valve on the filler neck .. which as far as im aware is there to help fill the car up with fuel .. it allows air to escape the tank whilst fuel goes in ...

There is a lever under the fuel cap so that when the cap is removed it opens this valve .

I would check the pipes covered by the circles for any blockage .

You have a work around atm but im not happy with this .. i doubt you are either .. my concern is that the car is running lean .. because this is on the tank venting side the car will not adapt to this ( no adaption whilst venting ) .. a lean running engine can cause valve issues over a long period .. they burn out basically due to excess heat on a lean burn .

have a read and see what you think as at the end of the day this is just my assumption .. but also please bare in mind .. the only 2 times i have herd of this fault have both been due to no.7 .


I wish i did know how every part on every Porsche works and indeed how every system works .. but im afraid theres not a person in the world that knows that .. we just try and work things out as we go .
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infrasilver
Fast & Furious
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PostPosted: Sun Jan 06, 2019 8:31 pm    Post subject: Reply with quote

deMort wrote:

My opinion .. No.7 is called a Vacuum limiting valve .. so thats what it does .. i dont feel its a one way valve but i think its a vacuum valve that opens when there is excessive vacuum build up in the tank .. this will then allow air to enter ther tank either from the canister pipe that vents to atmosphere or the engine purge valve .. or perhaps even both .

Also think of just how much vacuum it would take to colapse a fuel tank .. that plastic is harder than steel .. its designed to withstand a serious car crash .

If it was me .. i would replace no.7 with a brand new pipe


I agree, if that does indeed flow air back to the tank to release the vacuum it will be the thing to change next, the clue is in the name Rolling Eyes

This valve on the pipe does have an arrow moulded into it pointing away from the tank which usually shows the direction of flow on most cars parts I have seen before and does test only one way but I suppose that depends what pressure it can take in either direction.

I was previously amazed when the tank collapsed that the vent pipe from the tank managed to survive from being collapsed along with the tank. They are very stiff plastic but so is the tank.

I have also traced and checked all the pipework to make sure they are not kinked or blocked so this should be fine.
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Last edited by infrasilver on Sun Jan 06, 2019 10:30 pm; edited 1 time in total
 
  
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deMort
Zolder


Joined: 21 Mar 2015
Posts: 5723
Location: Brighton


PostPosted: Sun Jan 06, 2019 8:48 pm    Post subject: Reply with quote

My concern .. and i mean huge here .. we replace these bits but have no way of checking if it has actually solved the fault .

I certainly dont want to be wrong here .

Another collapsed tank doesnt bear thinking about so a bit of a bodge but something i think i would be doing in this case ..

I have a vacuum / pressure gauge .. a cheap one from Mac tools .. you just fit a rubber pipe to it and plug it into what ever you want to measure ..

I would drill a hole in the fuel cap .. fit the pipe / gauge along with plenty of silicone to seal it .. fuel flap open and the gauge taped to the flap along with tapeing the flap to the wing.

I would then drive the car 20 miles to make sure there is no vacuum build up showing on the gauge ..

A bodge but it should show if there is still a fault .

A fuel filler cap is cheap .. a tank isnt .
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