Petrol tank making noises

[kwacker]

Now the petrol tank is starting to make some strange noises. It makes thunking noises, like the tank is expanding. There is also quite a vaccume when you take the petrol cap off.

Is there a breather hose that might be blocked?

Kwacker

Thunk!

[Cider Andy]

Tank venting is done electrically. Depending on the level of fuel (or rather air/vapour) in the tank and the ambient temperature it's probably normal. If it's a new occurrence, have a specialist look at the carbon cannister and purge valve.

[GreenV8S]

Don't know if there is supposed to be a breather (I'd have thought so), but that problem seems very common and is usually solved just by not tightening the fuel filler cap fully.

[chassis 33]

The breather goes from the tank, via a roll over valve to the carbon canister, which then vents to the plenum chamber as and when the ECU sees fit...I've never quite worked out what makes the ECU see fit though.

Regards
Iain

[GreenV8S]

If that's all there is, that's the problem. The carbon cannister should be vented to atmosphere. The engine should draw air *backwards* through the carbon cannister when the purge valve is open.

[chassis 33]

Oh, ok, have to say didn't pay vast amounts of attention to the details, after fighting for hours to get the bastard thing finally out!!!

Regards
Iain

[M@H]

kwacker, get the cannister out of the front wing (passenger side, behind a little hatch) give it a bit of a knocking and shake about, then put it back in again.. should solve the problem. At worst, you either leave the cannister off, get a new one, leave the petrol cap a little loose, or the other thing that some people do (which doesn't solve the real problem) is drill a small hole in the filler cap.

The clunking noise is the tank colapsing with the reduced pressure inside from the fuel pumping out to the engine.

Cheers,
Matt

[wedgie]

chassis 33 said:

I've never quite worked out what makes the ECU see fit though.

Think you might have hit the nail on the head here, chassis.

I have the same problem, though it is intermittent, so I suspect the electronic wizardry is what is failing. Hence I am loath to trying to get the carbon can out (as it's probably the least accessible part of the entire car and will be a b@stard of a job) only to find I'm not achieving anything.

Any ideas?

[zumbruk]

M@H said:

kwacker, get the cannister out of the front wing (passenger side, behind a little hatch) give it a bit of a knocking and shake about, then put it back in again.. should solve the problem. At worst, you either leave the cannister off, get a new one, leave the petrol cap a little loose, or the other thing that some people do (which doesn't solve the real problem) is drill a small hole in the filler cap.

Which is an MOT fail, BTW.

[M@H]

zumbruk said:

M@H said:

...or the other thing that some people do (which doesn't solve the real problem) is drill a small hole in the filler cap.

Which is an MOT fail, BTW.

...interesting. Well there must be quite a few Chims about with dodgy MOT's then

[wedgie]

From what I've heard on my other post on this subject, the ECU will cause the the tank to vent at 3000 rpm, which might well explain why I get major vaccuum problems when I have just filled up and had a prolonged spell at low revs (in town etc), ie tiny air space, and no venting.

All the more reason to never go higher than 2nd gear in a 30 limit... "I had to make all that noise to stop my tank imploding, officer"

Also see this: www.pistonheads.co.uk/gassing/topic.asp?t=161934&f=8&h=0

Edited by wedgie on Wednesday 7th June 19:34