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Old 20-07-2016   #1
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Fuel Smell

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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Old 20-07-2016   #2
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Re: Fuel Smell

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
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Old 20-07-2016   #3
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Re: Fuel Smell

Really useful post. I too have the petrol smell and in almost the exact circumstances you describe! Steve
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Old 20-07-2016   #4
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Re: Fuel Smell

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
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Old 21-07-2016   #5
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Re: Fuel Smell

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?!)
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Old 21-07-2016   #6
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Re: Fuel Smell

Hi, thanks, good explanation.
SteveD
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Old 23-07-2016   #7
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Re: Fuel Smell

Thanks for your info, Cribus. This post is definitely a keeper for the fall when I get all the little pre-winter jobs done.
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Old 23-07-2016   #8
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Re: Fuel Smell

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.
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Old 23-07-2016   #9
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Re: Fuel Smell

That bulkhead's a lulu to wriggle out, isn't it. I'm not looking forward to putting mine back
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Old 23-07-2016   #10
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Re: Fuel Smell

Quote Originally Posted by gar074 View Post
That bulkhead's a lulu to wriggle out, isn't it. I'm not looking forward to putting mine back
I'm sure Dave-m wrote in an article that he ground/filed a couple of milometers off each side to help in getting it back in out again in the future.
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Old 23-07-2016   #11
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Re: Fuel Smell

Correct, made so much easier, however know g the wriggle procedure helps
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Old 23-07-2016   #12
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Re: Fuel Smell

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.
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Old 23-07-2016   #13
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Re: Fuel Smell

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?
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Old 23-07-2016   #14
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Re: Fuel Smell

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.
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Old 23-07-2016   #15
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Re: Fuel Smell

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.
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