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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Sun Jan 06, 2019 9:40 pm    Post subject: Reply with quote

I think I have a spare fuel cap somewhere anyway so this is no issue, will order the vac gauge and update later in the week.
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Jan 08, 2019 5:22 pm    Post subject: Reply with quote

So while I am waiting for parts to arrive and the Vacuum gauge I got busy breaking stuff.

I found an old fuel cap so drilled that through in readiness for the Vac gauge to be bonded in place.



The next thing to get attacked was the vent valve pipe. I cut both ends off it to reveal what is inside without damaging the internals so I can closely inspect it.

The arrow I have previously mentioned showing direction away from the tank.



Now I have split this valve I can't really see how it lets air back into the tank, although the tiny holes may be able to do this as they go between both sides. I understand the US pipe is called the Vacuum Limiting Valve but here in the UK it is called a Vent Pipe.

Air being pushed from the tank lifts the diaphragm to release it into the Carbon Canister. If air was being drawn through it or there was any vacuum from the tank I can only see that it would create a tighter seal on the diaphragm not letting any air back to the tank.





The diaphragm seals against the centre hole.



And while I had the hacksaw out I cut the Carbon Canister to reveal what was inside.

It was obviously full of carbon particles.



The filter screen at the bottom goes to the fuel tank and the second one at the bottom goes to the engine purge valve. there is a foam filter at the base for this pipe. The top also has a large foam filter and this pipe exits to the open ended pipe under the gearbox.



I'm not sure this helps us understand this system much more but at least we can now see what is inside.
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alex yates
Le Mans
Le Mans


Joined: 06 Mar 2014
Posts: 15567
Location: The Ribble Valley, Lancashire

2000 Porsche 996 Carrera 4

PostPosted: Tue Jan 08, 2019 5:49 pm    Post subject: Reply with quote

I always thought there was going to be a big footprint in there Confused Grin
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2000 Manual 996 C4 Arctic Silver Convertible


 
  
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kurlykris
Indianapolis


Joined: 30 Jun 2014
Posts: 2329
Location: Warwickshire


PostPosted: Tue Jan 08, 2019 5:59 pm    Post subject: Reply with quote

How did all that gravel get in there Question Get Me Coat
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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6178
Location: Brighton


PostPosted: Tue Jan 08, 2019 7:46 pm    Post subject: Reply with quote

Thats facinateing to actually see inside these items .. ive never cut either appart so have only refered to the Porsche images till now .

Im not really any the wiser on how this valve works .. the small holes .. i dont see the point of them if its just a one way valve ( thats not normal ) but im afraid at the end of the day im going with my usual logic ..

I can see no other way of air entering the tank other than via no.7 .

If the fuel cap had some sort of pressure release then it would be that .. but it doesnt and the fuel filler tube is sealed by the fuel cap .

Im afraid i can only go with what i would do .. replace no.7 and fit a vacuum gauge so that it can be monitored.

Sometimes i do sit here and realise .. im telling you guys to do this and replace that .. i am in effect spending your money ..

Sometimes i sit here thinking i dont really know the system .. im working on what i would do or what i can work out and perhaps it would be better if i just didnt say anything .. dont get involved so to speak ..

I dont like to do that .. i will try to help even if like this thread .. im not totally sure of how the system works but i know it needs to be fixed so im doing what i can .

It still worrys me though .
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Jan 08, 2019 9:06 pm    Post subject: Reply with quote

deMort wrote:
If the fuel cap had some sort of pressure release then it would be that .. but it doesnt and the fuel filler tube is sealed by the fuel cap .


Funny you should say that, when I was drilling the fuel cap a spring came out of it, (which I thought was strange) I wiggled the inner and outer of the cap and it does seem to be in two parts, although the movement was very minimal. Question


deMort wrote:
Sometimes i do sit here and realise .. im telling you guys to do this and replace that .. i am in effect spending your money ..


I don't think anyone would worry about spending money on parts from your advice, the cost of any labour they would incur would soon outweigh that.
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Mac996t
Nürburgring


Joined: 26 Mar 2011
Posts: 480


2004 Porsche 996 Turbo

PostPosted: Wed Jan 09, 2019 1:33 am    Post subject: Reply with quote

The gray valve you’ve dis assembled, that reveals a lot. In your previous posts you say this valve only flows in the direction of the arrow allowing air to flow from the tank to the canister but not letting anything flow in the other direction.

Looking at your pics it looks to me like there actually is a route for air to go in the opposite direction. I think this is what the two groups of four small holes are for. They allow a small flow in the other direction by lifting the small orange diaphragms. If you blow through the valve it may seem like it’s only one way because in one direction (from tank to canister) it flows a lot quite easily. I bet if you blow in the other direction there will be a flow but only a small one, not much but enough to equalise the pressure in the tank as the fuel level slowly drops!!!

I think this is the answer to the mystery of how the pressure is equalised as the fuel level drops

Also looking at the design of the valve it will flow in the direction of the arrow when there’s more pressure in the tank than in the canister allowing vapours the flow to the canister eg on a hot day when the fuel tank heats up.

What's not so obvious is that if there’s a vacuum applied to the canister the valve will shut and prevent this vacuum from reaching the fuel tank even though that flow would be in the direction of the arrow too, so in this respect it behaves differently to a normal one way valve.

What do you reckon any of this make sense?!!

Mac
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Wed Jan 09, 2019 4:09 am    Post subject: Reply with quote

I think that is the missing piece of the jigsaw. The small holes must let air back the other way back to the tank. The 2 x 4 holes did have little diaphragms on them but I couldn't work that out at the time because they got damaged when I cut it apart but what you have said makes sense now.

So deMort is correct that this is the route the air must take. I will try to do a diagram later of how it flows. It must pull the air from the open ended pipe at the top of the Canister but as it has to go through the large foam filter and carbon particles it doesn't draw any air unless it does actually need it and the two bottom pipes that go from tank to engine have little restriction between them so that is the easiest direction of flow until the vacuum takes over.

Fingers crossed when the new valve/ pipe arrives and is fitted that it cures this. I'll still attach the vac gauge to see what is happening though.

That arrow has been a red herring all along, I don't see the point in that being there Mad
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Last edited by infrasilver on Fri Jan 18, 2019 9:58 pm; edited 1 time in total
 
  
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Jan 15, 2019 6:20 pm    Post subject: Reply with quote

I set my rig up that deMort suggested, using a vac/pressure gauge connected to an old fuel filler cap and sealed to act like a normal cap would by sealing the filler tube.





I had the gauge taped to the windscreen so that I could see what was happening while driving.

I also set my Gopro up as I couldn't look 100% of the time while driving.



I covered 40 miles on all kinds of roads, motorway, dual carriageway and local roads. I also used around 10 litres of fuel so this would have made a decent space in the tank to have to fill with air again.

Unfortunately after all this set up, the gauge didn't move at all during the whole 40 mile journey. I think this is a good thing and hopefully suggests everything is working as it should?

I will monitor the fuel cap when opening it to see if air is sucked in at all, this will only show up on a long run though.
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Last edited by infrasilver on Tue Jan 15, 2019 9:10 pm; edited 1 time in total
 
  
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911munKy
Montreal


Joined: 26 Nov 2014
Posts: 518



PostPosted: Tue Jan 15, 2019 8:52 pm    Post subject: Reply with quote

“the gauge did move at all”

should that be Didn’t?

Sounds like good news after a challenging journey, congratulations.
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Tue Jan 15, 2019 9:11 pm    Post subject: Reply with quote

911munKy wrote:
“the gauge did move at all”

should that be Didn’t?

Sounds like good news after a challenging journey, congratulations.


Edited to say "didnt move"

Yes, hopefully good news
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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6178
Location: Brighton


PostPosted: Fri Jan 18, 2019 9:51 pm    Post subject: Reply with quote

Sorry for the delay .. not been very well this week so not been online since Monday ..

Just make sure the fuel cap / vacuum gauge is properly sealed .. other than that you seem to have no vacuum buildup and hence you dont have a fault anymore.
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infrasilver
Fast & Furious
Fast & Furious


Joined: 04 Oct 2010
Posts: 8146
Location: East Midlands

2001 Porsche 996 Targa

PostPosted: Fri Jan 18, 2019 9:56 pm    Post subject: Reply with quote

deMort wrote:
Sorry for the delay .. not been very well this week so not been online since Monday ..

Just make sure the fuel cap / vacuum gauge is properly sealed .. other than that you seem to have no vacuum buildup and hence you dont have a fault anymore.


No problem at all kind sir.

I made sure the seal on the cap was tight and the pipe to the gauge was too.

I did half expect to see the gauge move in either direction, sucking or blowing when the valve opened either way but it didn't budge so hopefully that is the end of it? Need to take it out for a long run at some point soon just to confirm.

Get well soon.
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deMort
Long Beach


Joined: 21 Mar 2015
Posts: 6178
Location: Brighton


PostPosted: Fri Jan 18, 2019 10:02 pm    Post subject: Reply with quote

logically there should be no vacuum buildup hence the gauge would remain at zero...

Considering just how strong the fuel tank is then i would guess at a negative 5 bar or more to collapse one ..

I did a conversion to a vacuum for this .. it made no sense to me ! so i stuck with negative bar .. you know what i mean Smile
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