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Broken down, cut out. Fuel tank collapsed, bent sender

I have eventually got the fuel tank out and on the deck, it was a bit of a nightmare and very tight trying to get it out from between the subframe rear rails.

Once I got the plastic covers, cross braces and tank skid plate off I could see how much the tank was gurning, I would guess it's half its original capacity now.

The base should be flat.
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After dropping the subframe, steering rack and 6 coolant hoses I dropped the tank off its cradle.

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This was the nightmare bit, the tank wouldn't fit between the subframe rails so a big foot and a lot of kicking eventually saved me dropping the whole subrame and suspension off the front.

How I will get a full size tank back in is anyone's guess.

So with the tank off I could see places I have never seen before and treated a little bit of surface rust and the seams with POR15.

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I also noticed my power steering pipes were a bit crusty near the end joints so these got cleaned up and more POR15 coated on them. I also did the brake pipe that runs across the front of the steering rack as this looks a nightmare to get to to with everything still in place.

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And the tank out.
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The new tank arrived today so will start refitting everything over the weekend, got a used one for £33 rather than pay the OPC price of £2000!
 
£2k :eek: :floor:

Taking the piss.
 
Have you figured out where the 3rd pipe from the canister goes to? Is it just ambient? If it is, should it have a little filter on it?

Have you considered a new fuel cap for the replacement cap? Can't remember if I asked you that previously.
 
Ghianightmare said:
Have you figured out where the 3rd pipe from the canister goes to? Is it just ambient? If it is, should it have a little filter on it?

Have you considered a new fuel cap for the replacement cap? Can't remember if I asked you that previously.

I have so far traced the pipe to the rear of the car where there is another connection under the car and then goes up to what looks like the rear of the engine, so I'm now assuming it goes to the engine but as the car is still on the ground at the rearI can't trace any further at the moment.

The fuel caps only usually cause problems if they don't seal when the rubber seal degrades and cracks, mine seems like it seals very well.
 
Have you tried an airline to see if you can blow the old tank back to shape?
 
My guess is galvanised steel, sheet steel collapses easily with a vacuum.
 
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.
 
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.

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

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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.
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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.

43598463900_8ddf5756cb_c.jpg


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.

44691256584_ff72d5d217_c.jpg
 
alex yates said:
I'd check how much it takes to fill it. Could have an imploding fuel tank.

:wink:
 
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.
 
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 .
 
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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