Technical Fuel Smell

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Technical Fuel Smell

Cribus

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In case it helps anyone else, I finally seem to have got rid of this smell that would come and go at random. Turns out it was coming from the fuel vapour segregator, which lives in the gap between the nearside rear inner and outer wings.


As standard, pipes from the two valves on the top of the fuel tank take fuel vapour to the segregator (and release tank pressure). From the segregator another pipe takes the vapour away, it goes down through the floor next to the tank and makes its way to the charcoal canister situated under the bonnet, beneath the coolant reservoir (on my 96 car anyway). After trying many other things which included sealing off the charcoal canister and running the vapour exit pipe to atmosphere beneath the rear end of the car (after reading that the canister can be the source of the smell, which it turned out not to be in my case), I finally sealed off and isolated the segregator so the vapour now goes straight from the tank to atmosphere at the rear underside of the car. And the fuel smell in the cabin and boot is finally gone.


So in other words, what happens now is that the two pipes which take fuel vapour from the valves on the top of the tank now go to a T-piece and a third pipe then leads from that down through the floor to the rear of the car where the vapour exits. The original pipes going to and from the segregator are now sealed so that the unit is isolated and does nothing.


What confused me in the beginning was that the smell would usually be present when the car had been parked, and when you started up and drove off the smell would go. But if you then opened a window, the smell would return which made me think that it must be coming from the front of the car, presumably under the bonnet somewhere. But what I think was happening was that when you opened a window the incoming wind would create pressure in the rear of the cabin which would draw out the fuel smell from the tank area behind the seats and bulkhead. Now the smell doesn't appear no matter how much gale blows in from the windows.


I hope that helps some of you who have the smell. There seem to be many possible causes though, I went through other checks and changes before finding this cure for my car. I appreciate that having the fuel vapour exiting to atmosphere isn't ideal, but you really can't smell it even if you crouch down towards the underside of the boot where the vapour leaves the pipe so the amounts involved can't be that great. Whether this setup would be noticed and frowned upon by an MOT man I don't know (luckily we don't have MOT's over here in the IOM). But I wouldn't think that a thin black rubber pipe zip-tied to the boot floor would be likely to catch anyone's eye.


Biggest pain was getting the rear bulkhead out. Undo the screws, grasp the nearside end of the bulkhead at top and bottom and pull it towards the front of the car, especially at the bottom, until you can slide it out of the driver's door. That's after removing the bits of black plastic trim etc at the sides of the bulkhead that are in the way. To create the new vapour pipe circuit behind the bulkhead all I bought was some black fuel pipe (6mm inner diameter to push on to the exiting blue pipes which I snipped) and the plastic T-piece. Since finishing the job I've filled the tank (never done that before!) and checked that the tank is being vented properly by removing the cap every so often to check for pressure hisses, and all is fine. Runs perfectly and no smell.
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Thanks Cribus, not a problem for me yet. Hopefully if it does occur I'll now know the most likely way to sort it now. This is why forums such as this, are so important. Stuart
 
Hi Cribus,
Thanks for the post. The 2 pipes you cut; are they pipe number 3 and 5 on the eprdrawing and you blocked off the other 2 pipes from the segregater canister in the rear wing?
Cheers SteveD
 
Yes I snipped 3 and 5 a few inches away from where they join the tank valves. Pipes 3 and 5 are different diameters on my car. Pipe 3 is thicker and pushes straight on to one arm of a 6mm O/D plastic T-piece. Pipe 5 is thinner and after snipping it I ran new 'push-on' 6mm I/D fuel hose to the T-piece. I then snipped pipe 6 and connected that to the remaining arm of the T-piece with more of the new hose (6mm I/D again) so that fuel vapour goes straight from the two tank vents down through the floor and to the charcoal canister (or not in my case).


To seal the segregator (I couldn't work out how to remove it) there were three stubs of old pipe left connected to it so I simply plugged the ends with bolts of the right diameter screwed in to them. Just to stop any smells from anything left in the segregator.


It's confusing to describe but straightforward in practice. As long as you have a metre or so of the hose and T-piece described (I got both via eBay) and some snippers then it's all do-able (assuming that your cars' pipes etc are the same as mine of course !) With mine it took some force to push the new hose on to the stubs of the old lines which is good of course as there's little chance of them coming adrift.


I suppose I should just cover myself by mentioning that others trying this must do so at their own risk - although none of these lines carry liquid fuel the vapour is still highly flammable of course so please be careful not to cause any sparks etc especially if the smell is already present at the time. I'm not a professional mechanic by any means, all I can say is that the smell is gone in my car and the tank is still venting properly and all seems fine (tempting fate or what?!)
 
Thanks for your info, Cribus. This post is definitely a keeper for the fall when I get all the little pre-winter jobs done.
 
Glad it was of help and I hope it works for other cars. Although I'd already isolated my charcoal canister and run the vapour out the rear, if I was starting out now I'd keep that in the loop as it turned out not to be part of the problem. So I wouldn't mess with that part of the system unless there's clearly something wrong with it.

And to remove the bulkhead, I forgot to mention that obviously the centre storage box and handbrake surround need to be loosened and raised forwards to let the bulkhead out, in addition to removing the plastic trims at each side.
 
The mistake I made in the beginning was to try to pull the bulkhead upwards, not realising that the aim is to slide it out sideways, through the driver's door. To achieve that the bulkhead's nearside edge needs pulling away from its usual position, towards the back of the driver's seat until it can be slid out across the door sill. Surprisingly it was really easy to slide it back in the same way, no bother at all. Getting the screws back in place was a bit awkward here and there because the bulkhead seemed to have bent slightly getting it out, but having a second person pushing it into place would have made it much easier while you get each screw back in.
 
Hi Cribus,
Just to sum up, all you had to do was remove the segregator out of the system. What is this supposed to do anyway? Obvious answer is segregate, but segregate liquid fuel from the fumes. If the vapours now go directly to the charcoal canister will this overload the charcoal canister or fload it with fuel? I guess that the charcoal canister just absorbes the fumes safely and there is no petrol reaching the canister anyway. (Original system belt and braces).
I presume you didn't change the segregator because it was just easier to bypass it. Okay I am probably over thinking it.
Any thoughts?
 
Good question - like you I assume it's meant to intercept any liquid fuel that manages to escape from the tank top valves whilst letting vapour reach the charcoal canister. When I snipped the pipes to and from the segregator there was no hint of any liquid fuel from them. I suppose I'm happier with my setup as I know that any slight liquid fuel that might be able to make its way from the tank valves down the pipe will be expelled rearwards beneath the car rather than perhaps make its way forwards to the canister. So maybe that's a reason to divert the vapour away from the canister as I'd already done, especially as I read posts from a few years ago indicating that the canister can cause problems, maybe with age. There was even a post pointing out that the fire-gutted B's you see in the occasional online image seem to be most fiercely burnt in the area of the canister (but that's also near where the rubber fuel lines join the rail of course, right above a hot engine).

I think replacing the segregator would be a real struggle to do, it's hidden away between the inner and outer wings and is mounted firmly but I couldn't see how or even get a proper grip on it. Not a user-friendly location by any means! Personally I'm happiest having the smell gone and any slight escaping liquid fuel heading rearward rather than towards the engine compartment, it just means doing a bit of work beneath the rear of the car as well as behind the bulkhead. And it means my other half is now finally prepared to sit in my B rather than us having to use her Yaris.
 
Actually thinking about it - if the segregator catches any liquid fuel from the tank valves, what does it do with it ? It's only a small unit and there are just two pipes in (from each valve) and one pipe out, leading to the canister. Perhaps any liquid drips into the base of the segregator, below the outlet and slowly evaporates and the resulting vapour then makes its way to the canister.
 
Yup i don't think thereis anything high tech or a crucial need for the segregator, perhaps over doing the elf and safety with the effect of providing extra problems in the cars old age. SteveD
 
Thanks for this post, I'm suffering the same problem and plan to tackle it this weekend. In answer to some earlier questions as to the purpose of the Fuel Vapour Separator the manual I have states:
"Fuel vapour from the anti-rollover valves reach the separator located on the left rear wheel arch through two ducts. The separator consists of an outer case and closing several perforated plates on which a proportion of the fuel condenses. Condensed fuel returns to the tank three ducts, while vapours leave the central duct to the carbon filter. The two-way ventilation valve located near the charcoal filter allows vapour to flow back to the activated charcoal filter when the pressure in the tank causes the valve open. The valve also allows ventilation air coming from the activated charcoal filter connection to pass to the tank when the latter is under a slight vacuum."

The only part that worries me with this fix that "when the engine is running, the ECU turns on the carbon filter flushing solenoid (located near the charcoal filter). This allows vapour to be taken up by the engine in order to flush the carbon filter."

I'm wondering what effect the fix will have on that solenoid and the ECU and engine performance if it is just passing air through. Am I sounding paranoid?
 
Many thanks, I'm not entirely clear on some of that but it sounds a bit like what I suggested a few posts ago as regards what the segregator does. A bit. To be honest I'm happier with my setup whereby both the segregator and the front canister are isolated and no longer do anything.

I've been driving with the canister isolated for months and it's been running perfectly. Isolating it involved disconnecting the pipe that takes vapour to the canister, at the click-together connector which is just beneath where that pipe goes down through the floor next to the tank and emerges beneath the car, and running a new length of pipe rearward from that connector so that the vapour exits beneath the rear bumper. And under the bonnet I snipped the blue pipe that runs between the intake manifold and the canister and plugged both ends, to isolate the 'out' side of the canister.

And of course isolating the segregator is described above. I've been driving daily with that isolated for a couple of weeks now and again all has been fine. Absolutely no fuel smells even with a full tank, and no pressure build up in the tank. Previously, the smell would be there randomly, on and off just about every day, both in the cabin and boot (there's a passageway between the tank area and the boot, through which the aerial wiring runs, so I assume the smell gets to the boot through there. You'll see it once the bulkhead is out. Oh and you may want to check the inner arches for rust while it's out, mine were fine thankfully).

My setup may be overkill as I don't see how liquid fuel could emerge from the valves on top of the tank in sufficient quantity to reach the canister at the other end of the car, unless perhaps the car rolled over but if those are anti roll-over valves as described in the extract then presumably they close if the car inverts anyway (or should do). I hope you have success, please update to say how you get on !
 
Well, I finally found the source of my fuel smell problem and it wasn't what Cribus had found and solved. When I got to the tank (following the excellent instructions in this post) i noticed fuel leaking from around the pump seal. One very clever previous owner (or mechanic) replaced the fuel pump in the tank but didn't seat the pump squarely on the seal so it was crimped in one spot. They subsequently overtightened one of the stud bolts that hold the pump in place and snapped it off. So I had no seal and one stud missing, hence the over-powering smell - let alone danger.

Quickest solution was to get a tank from Henk at Barchettaparts. It was Godsend and came complete so all I had to do was take out the old one living all the hoses in place and reconnect them. Lucky for me the pump in it worked fine and now I have a spare. Best part is the smell is gone and I haven't had to terminate any of the hoses or use Cribus' suggestion.

Just one thing I did notice. The segregator canister that Cribus disconnected is a sealed unit and I can't for the life of me figure how any vapour could escape from it unless it was cracked or the connectors weren't on tightly. It's a mystery.
 
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Glad to hear your smell is sorted, I don't envy you changing the tank. It just goes to show that no two cars are the same I suppose. The fuel pump seal was one of the first things I checked on mine but all the tank connections and seals, pipes, clips etc were dry as a bone.

Maybe my smell was coming from one of the pipe connections to or from the segregator rather than from the unit itself but I didn't get to examine it closely as I couldn't even work out how to detach it to have a look over it. I've been using my car daily for weeks now and there's not even a hint of petrol smell in either cabin or boot whereas before it was a daily issue.

I'd be interested to hear how others get on, I went right round the houses for months tracking down the cause of the smell in my car.
 
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