Fuel leak in boot (trunk)

[simonknee]

Hi all,

I changed my knackered, boot mounted, Burlen fuel pump for a Facet (1.5- 4psi) square jobby as part of the overhaul.

On first run there was a splendid leak from the outlet union. From the pump side not the hose side. I tightened this up b'stard tight and later added plumbing tape as well. I can no longer see any fuel weep. I replaced all the hoses. I also removed the fuel reg for now. So all I have is tank-hose-filter-pump-union-hose-engine bay. (the filter is the one that goes straight on the pump)

After I turn off the engine and open the boot there is no fuel smell. However next morning the boot will definitely smell of fuel. I imagine it is still this union but how do I tell since there is never any visible liquid.

Could there be residual pressure left in the after the engine is turned of but the pump runs on for a second and that this is forcing it's way out. Maybe it's a faulty unit.

What I need it a good way to diagnose where this is coming from. Does anybody have any tips.

[oldelanman]

Try powering the pump without starting the engine. This will pressurise the system and you may then be able to spot if there is a leak. Spraying the union with foot powder might also help to show it up.

Regards,

[simonknee]

I've done the first but I think it is too slow a leak. I like the foot powder trick though.

If it is the screw thread of the union into the facet what can I use to promote a better seal.

[Heuer]

I had a similar problem. Turned out to be a cracked seam on the tank - they are very fragile.

[oldelanman]

If it is the screw thread of the union into the facet what can I use to promote a better seal.

Hi Simon,
I believe the thread in the Facet pump is nptf which is a dryseal taper thread and, in theory at least, should not require any sealant to achieve a pressure tight joint. If your joint is still leaking you could try a liquid sealant - Loctite do several, check out their website.

Regards,

[simonknee]

I believe the thread in the Facet pump is nptf which is a dryseal taper thread and, in theory at least, should not require any sealant to achieve a pressure tight joint.

Had to google ntpf to find out what it meant. Interesting I never new this existed. So assuming the facet is nptf and that the first time I used it I had no teflon tape then the fact it needed to be b'stard tight to stop an obvious weeping perhaps means that the unit was faulty in the first place?? Or does it mean I need a bigger spanner???

When you suggest loctite do you mean one of their threadlockers? I have a bottle of ThreadLocker 243 which the tech specs from loctite say:

Gasoline Resistance (Aged under conditions indicated and tested @ 22 ?C.)
% of initial strength
100 h 100%
500 h 100%
1000 h 95%
5000 h 95%

Looks good but I know little about this stuff.

However I have been searching on the use of ptfe tape and I think there is some nonsense written about it. Whilst is does not dissolve in gasoline repeated insertion and removal of the joint could result in little threads of ptfe getting stripped off then pushed down into the fuel line. Hopefully the filter will catch it but these are not desirable.

[simonknee]

Hmm, this still does not make sense. I have turned on the pump and left it running with the engine off. You would have thought that getting up close with your nose would reveal a smell but no, nothing at all.

It is only after leaving the car for a couple of hours AFTER you have been driving that you get a build up of petrol fume in the boot. I cannot understand why this would be.

[Elan45]

Simon,

Shortly after restoring my Elan SS, we made the trip to the LOG in Vermont that year. When we arrived, I noticed a petrol smell that I isolated to a crack in the fuel tank around one of the mounting studs. We were in New England for over a week and at least once a day the tank had to come out for application of a steptic pencil to slow the leak. After we returned home, the tank was repaired by brazing and it was fine, so your smell could be coming from something other than the pump and its connections.

Roger in Ohio

[simonknee]

I think you may be right. I good investigation of the tank revealed some kind of repair gunk at the bottom of the filler neck. It had been painted over but was starting to lift. I prised it all off and the welding underneath looks OK but I have applied a blodge of epoxy metal putty to the area. I'll know tomorrow morning whether this helps at all...

[oldelanman]

Had to google ntpf to find out what it meant. Interesting I never new this existed. So assuming the facet is nptf and that the first time I used it I had no teflon tape then the fact it needed to be b'stard tight to stop an obvious weeping perhaps means that the unit was faulty in the first place?? Or does it mean I need a bigger spanner???

When you suggest loctite do you mean one of their threadlockers? I have a bottle of ThreadLocker 243 which the tech specs from loctite say:

Simon,

This may be irrelevant in light of your last post - you just beat me to the submit button !

It could be that the thread on your union does not match that in the pump. npt is also a taper thread which looks the same as nptf but the threads are slightly different. The two are compatible and will screw together but will not form a fluid tight joint without using a sealant. Where did the fitting come from - was it supplied with the pump? By the way I'm no expert on threads I'm just Googling around like you ! Loctite 243 should be OK as they say it's suitable for use on carburetors and oil pressure switches. I'm sure you know this but whatever you use apply it to the male thread only so it doesn't get into the pump or fuel lines.

Another thought - have you checked the clamps are tight on you fuel filler neck rubber tube ?

Regards,

[simonknee]

You wouldn't believe how tight my clamps are!!!

brass unions came with the pump...

http://www.fastroadcars.co.uk/shop/inde ... oductId=66 (pic doesn't show unions)

Don't know how I would tell an npt from an nptf with an appropiate thread gauge

[simonknee]

Ah I did not read properly... I've never check the fuel filler clamps ...

[simonknee]

Still smelly

So today I shall take my nose carefully round the seams of the tank (those I can get at anyway). Since it takes hours for the smell to build up I am hopeful it is in a dry area rather than wet.

Question? are petrol fumes denser or lighter than air?

[lotuselanS3]

Hello Maybe I?m wrong but could it be that the smell comes from the hose that?s between the Tank filler neck and the Filler? Thats a common problem on Cobras. By the way my Elan is also smelling and to be honest I gave up on this problem long time ago. But this threat make me think of it again.
cheers
Stephan

[simonknee]

Yeah! Found something

Following my nose led my to the union of tank and first hose. Faint but definitely petrol. Pulled off hose and cleaned the tank pipe as there was some paint on it. Inspected hose and the fabric braid under the metal braid seemed to be a little damp. This was probably just spillage when I took it off right? Wrong! About 2 cm back under the braid there was a small puncture in the rubber hose!!! This is new hose so I did this somehow during assembly.

Braided hose is great but you can't see the condition of the rubber underneath.