Can't fill the tank - 80 litres max

[MikkiJayne]

Its certainly concievable it could be that. What I think is happening is that one or more of the tank vent lines (6-9 in that pic) are unable to vent and so the tank fills to the level of the filler neck leaving a large air pocket in the top of it. Its not clear from the diagrams where those lines go, but I think they go in to the large assembly behind the filler neck first, which then has a single line (4) over to the charcoal container. In theory the only open point is 5 which is right on top of the tank.

I won't mind too much if its the charcoal container which is blocked as thats relatively easy to change. I will be a little grumpy if its the thing behind the filler neck as that has pipes everywhere and many rusty fittings. However, I shall be very pleased if its either of those compared to having to swap the whole tank!

I took all this stuff out of Sergey's car relatively intact so I need to get that off the shelf and see how everything goes together.

Its been pointed nose-down overnight so I'll nip up to the workshop (vigorously!) in a bit and see if I can get an extra couple of gallons in there. If so, that would suggest its a partial blockage somewhere which just can't vent as fast as a petrol pump can put fuel in.

[MikkiJayne]

Definitely a venting issue. I parked on a slope at the front of the workshop with the filler neck corner highest and was able to get another 2 gallons in, with the gauge now showing full.

The first gallon went in no problem, but the second took ages as the neck of the fuel can would get submerged in fuel in the filler neck and airlock itself. It waited until the level dropped a bit, got a gulp of air and let some more fuel out, and carried on like that for several minutes.

Following that there was a prolonged gurgling from the tank as the level settled. Pressing the vent in the filler neck changed the gurgling but didn't stop it.

Need to investigate the venting system...

[HPsauce]

The mystery would be what could be partly blocking the system and how did it get there?
And would filling the tank completely, as you have done, then letting the level drop, dislodge, free or open it up?
Sounds like an excuse for more spirited driving...…..

It also seems more likely that it's the central upper breather that is the problem.

[HPsauce]

Originally Posted by MikkiJayne

Its certainly concievable it could be that. What I think is happening is that one or more of the tank vent lines (6-9 in that pic) are unable to vent and so the tank fills to the level of the filler neck leaving a large air pocket in the top of it. Its not clear from the diagrams where those lines go, but I think they go in to the large assembly behind the filler neck first, which then has a single line (4) over to the charcoal container. In theory the only open point is 5 which is right on top of the tank.

How accessible is the charcoal container? Is it possible to disconnect its combined input from the tank vents (4 in the diagram) and see if it then fills normally (just the last 2 gallons from a can)?
That would narrow it down to the charcoal canister or plumbing.

By the way what is line 3? Is that a vent from somewhere else in the fuel system?

[MikkiJayne]

Line 3 goes to the front to the N80 evap valve.

The charcoal can is equally as vexing to get to than the 'expansion chamber' on the other side (which is what Elsawin calls the big lump all the vent pipes feed in to). Arch liner out, then a bunch of hose clamps, although all stainless rather than the sad rusty lumps on the other side. Although, I had the left side arch liner out when I repaired the sill so that's like to come apart more easily than the right side.

It could be disconnected from either side tbh. I might try that before I get out the parts cannon

[HPsauce]

Originally Posted by MikkiJayne

It could be disconnected from either side tbh. I might try that before I get out the parts cannon

That was in line with my thinking, disconnecting a single pipe at one end or the other would hopefully be a lot easier than removing a unit, but just as useful for diagnosis.

Follows my basic diagnosis rule: only change one thing at a time..... (unless you're very very clever)

[MikkiJayne]

These are some pics I took of the pipework. They actually doesn't help at all with understanding how the vent system works, or indeed what the problem might be, but maybe someone else will be inspired...

The vent lines from the top of the tank. The small one is the front right, medium (blue stripe) is the front left and front upper combined, and the large (blue and yellow stripes) is the upper rear.



This is what Elsawin calls the 'expansion unit', shown roughly in the orientation it is in the car. The fitting to the top right of the pic is the top surface and is horizontal. This contains the gravity valve, and feeds to the valve for the vent release in the filler neck. The upper of the hoses to the left is the one which goes to the charcoal can.



In this view you can see that the upper rear tank vent goes straight to the top of the filler neck.



Top three go to the tank, to blue/yellow, black, and blue in top-to-bottom order.



Hose for the charcoal can



This is the pipework from the charcoal can. Top right is the line going forward to the N80 valve. Lower middle is from the filler neck assembly.



Closer view. Right is the pipe to the filler neck. Left is the vent to air from the can. This is a closed system with no openings other than these three pipes.



Given that the main tank vent goes straight to the top of the filler neck I don't see how that can be the cause unless the hose has collapsed. Any filling solution (petrol pump or gallon can) is putting fuel in below where this pipe attaches

If the charcoal can is blocked then that could block the lower tank from venting via the expansion unit, but the top of the expension unit can vent in to the filler neck through the vent valve so its still a mystery.

I think I need to burn some fuel off and then pull the driver's side arch liner out and check all the hoses are intact. If they are then I'll disconnect the charcoal can in there and see what happens.

Alternative suggestions welcome though...

[HPsauce]

That's not logical, captain...…
Either you've misunderstood what you have in front of you. Or it was installed incorrectly, or (something else)….
It doesn't make sense for the top of the tank to vent directly to the filler tube, it surely must go via the charcoal canister?
Surely the whole point of all this complexity is vapour recovery?

Although on second thoughts it must need to vent quickly somehow during filling? I know there are some types of fuel fillers that include vapour capture.

[HPsauce]

Originally Posted by HPsauce

That's not logical, captain...…

Or more likely it is and it's me that's confused.

So I've just been reading up on the general principles around the canister, something I knew nothing about before....
They collect vapour given off by the fuel that might otherwise be vented to the atmosphere at any time, typically through temperature changes while parked.
So they are in line to a pressure release valve and vent de-vapoured air, in this case presumably via the pipe noted as 5 on the earlier diagram. I'd guess the pressure valve is incorporated into the cylinder unit somehow.

When the engine is running and reaches certain conditions another valve opens and air is sucked in through the canister (presumably also via pipe 5) to purge the vapour from the carbon into the engine air intake.

I struggle to see how any of that could cause an airlock blocking 2 gallons of fuel entering the tank.

Though I'm still not clear about pipe 9 and the vent into the filler tube. Most vapour will be coming up pipe 9 so that needs to vent when under pressure via the canister. I guess when the filler cap is open it just passes by the canister and into the filler tube; when not fuelling that will be sealed to the outside so it can somehow route back to the canister.

This contains the gravity valve

what does this do?

I'm wondering if you dare connect an air line (if physically possible) to the vent into the filler tube and blow back down it?