Technical Vacuum in petrol tank

[cheapomulti]

I'm hoping some one has solved this little problem before.

Our multipla has started developing a serious vacuum in the fuel tank is there a breather pipe for the tank or air admittance valve ???
or is this a fault with the vapor trap/valve and or pipe work.

the ePER show several pipes and a valve in the top of the tank.... is this a known fault.?

it wouldn't bother me but if i forget to remove the cap now and again to equalize pressures the car starts 'holding back'
Once the caps been off for a few seconds she runs lovely.

I have used Multiecuscan to activate the vapour trap valve under bonnet and its buzzes when activated ... is this what its supposed to do.

any help would be greatly appreciated

 

[pete123]

I have has this problem I had to give the car to a fiat dealer as there is a pipe on top of the tank witch over time becomes blocked with junk all I remember him saying was he had to drop the tank it did happen again 6 months later and I replaced the fuel cap and it never happened again so go with the fuel cap to start as there r breathers In that

 

[cheapomulti]

Thanks Pete
following your post a got my draper borescope out and yes you're correct looks like there is a vent pipe on the top of the tank .... I have to admit I didn't fancy dropping the tank to try to trace & clear the pipe .. So i have modded the filler cap to allow the tank to vent but still make it hard for water/dust to enter the tank ...i.e not by removing the seal at the filler neck but by disassembling the cap and drilling 4 holes in the vertical sides in the outer skin only then fitting a disk of tyvek filter material into the lid (it was left over from a material handling system I built on a previous job)...there are a set of vent holes there already to allow the overpresure valve built into every modern cars filler cap to vent if needed.
Possibly far too over engineered but i was at a loose end till some parts turn up to get the multi back on the road.

any way I 've started her up and no more tank vacuum...hopefully that's the end of that.

 

[cheapomulti]

Oooops

 

[marks152]

Im not wanting to P**s on your fire but yes the tank will now breath but should you have an accident and your car turn over or on its side then now fuel will spill out which helps to BBQ you alive. You should never perform such a dangerous mod unless your not bothered about your life. I would be sensible to fix the fault rather than create another.

 

[Most Easterly Pandas]

basically what i did was to unclip the locking cover from the cap

there are 4 clips just use a small flat screw driver to release them carefully.

then drilled 4 holes between the ratchet and over pressure valve retaining clips

Then i put 4 layers of breathable tyvek filter material cut into rough a donut shape into the top of the lower part of the filler cap

and simply pushed it all together gain ..

I'm sure just drilling the holes would have sufficed but I got carried away.

An illegal modification, will fail the MOT should the cap ever be a testable item. It'll also mess with the evaporative system of the car and enable loss of fuel in the summer, and as above be deadly in an accident.

In addition to this you risk posing a real hazard to other road users, spilling fuel all over the road on bends after brimming your tank on fill up.

Remove the cap and change it for a legit one

 

[cheapomulti]

good point ... new cap on order £5 wasted.....still need to fix the vacuum problem tho...looks like I'll be dropping the tank after all.

 

[cheapomulti]

.OK so new fuel cap fitted and vacuum problem is back ..
I spent some time some time at lunch time and dropped the tank (front bolts only) as well as dropping the filling tube and all vent / vapor pipe work.

Did you know the vent pipe for the tank connects to a small tank mounted at the top of the filling tube (but not connected to the filling tube) , On top of this tank is a valve with a 15mm ball bearing in it , If you want to remove this simply rotate it anti clockwise its on a bayonet fixing ...I assume this is a roll over valve to stop liquid fuel entering the vapor/ purge system should the car roll over or simply operate on a severe incline.

Any way this seems to be a closed system that the purge valve draws from (the valve on top of the vapor /purge tank under bonnet).

I did blow down the vent pipe into the fuel tank and with my ear of the filling pipe (cap removed) you can hear the air entering the tank.... so the vent pipe work was not blocked.
So i took a look at the purge valve under bonnet
With the valve removed I sucked on the pipe(still connected to the valve) that connects to the manifold and vacuum is present at the bottom port that would connect to purge tank(under bonnet) and vapor line from the tank.
This must be allowing the manifold vacuum to put the tank under continuous vacuum.

Or of course the valve is normally open and closed by the ecu ... though i suspect the opposite is true as this would leave the system open to atmosphere all the time the cars not being driven

unless I'm missing some thing obvious .

 

[Adrian Bravo]

Hey, are you sure its not supposed to have a vacume? Because the 1996-2001 Bravo's of the same era are supposed to have a vacume in the tank. Heres page 169 of my manual.

 

[pete123]

The pipe running across little to big tank is for reserves fuel if there is nothing blocked down there the only other way is as u say the fuel lines that run to the rail on the manifold I did see u done some dangerous petrol capping not advisable bit as u say with ball bearing etc I don't think it's cuts the fuel from the pipe and u would be cooked as car rolls sparks fly ill do a bit of homework and come bk to u as I would now suspect something inside the tank as this is a common problem for the 1.6

 

[Most Easterly Pandas]

Hey, are you sure its not supposed to have a vacume? Because the 1996-2001 Bravo's of the same era are supposed to have a vacume in the tank. Heres page 169 of my manual.

I was thinking this, and then thought I was wrong, glad I'm not.

 

[pete123]

Ok how can fiat say that's normal as if it just keeps sucking and can't breath at some point it will weaken the plastic tank or other parts this prob can be related to head gasket believe it or not

 

[Most Easterly Pandas]

Ok how can fiat say that's normal as if it just keeps sucking and can't breath at some point it will weaken the plastic tank or other parts this prob can be related to head gasket believe it or not

There will be a pressure relieve allowing limited air in - if there wasn't the car wouldn't physically run as without air entering the tank to displace used fuel you can't extract fuel.

How do you connect it to HG failure out of interest then? Can't see the connection myself.

 

[pete123]

Was looking around they say its like a warning sign of pressure building up etc before it goes ces under air locks etc inc water petrol diesel I only state what I read and I do a lot of reading when ur a full time mechanic for the older car u need to it also states it in my a.a book that they carry with them and I will post the exact part tomorrow for future reference

 

[cheapomulti]

The pipe running across little to big tank is for reserves fuel if there is nothing blocked down there the only other way is as u say the fuel lines that run to the rail on the manifold I did see u done some dangerous petrol capping not advisable bit as u say with ball bearing etc I don't think it's cuts the fuel from the pipe and u would be cooked as car rolls sparks fly ill do a bit of homework and come bk to u as I would now suspect something inside the tank as this is a common problem for the 1.6

nope not a reserve fuel tank ...its at the very top of the filler pipe but not connected to it (pipe wise) ..the valve with the ball bearing is only connected to the vent pipe from the tank and plugs into the tank which is other wise only connected to the vapor purge system.

 

[cheapomulti]

Hey, are you sure its not supposed to have a vacume? Because the 1996-2001 Bravo's of the same era are supposed to have a vacume in the tank. Heres page 169 of my manual.

I have a very high vacuum build up not positive pressure as stated in the manual you posted.

If it wasn't causing problems i wouldn't be bothered with it ..

 

[cheapomulti]

so the tank I'm on about is circled here...the big red arrow is the pipe leading to the purge valve under the bonnet.

if you ever have the pleasure of taking the entire system out as i did you'll find the the only vent / purge route is via the purge valve/tank (part number 4) under bonnet .
which you can see here.

 

[cheapomulti]

read this guys
http://www.ehow.com/how_10025653_diagnose-purge-valve.html

mine leaks.... badly

I've just contacted my local fiat dealer via email ... couldn't get through on phone...If I don't get a reply I'll phone em Monday.

 

[pete123]

Nice diagrams I'm guessing u dropped the tank etc how did u find out about the purge tank diag kit or just a bit of hunting around

 

[cheapomulti]

Yes I've had the entire tanks system on the floor , plus I had a look on the bimmer forums as a lot of 5 series from early 90's till mid naughties suffered , from bad purge valves causing loads of strange problems. Vag group cars from tbe same time had the same problem ... I have a V twin vacuum pump with reg and guage most commonly used to bleed problematic diesel cars, I used this .... Total vacuum loss in less than 2 seconds .... I,ve since been told that the valve should be closed during idle and only open during hard acceleration to draw fuel fumes from the vapor purge tank....it was also suggested that my purge canister/tank may be blocked causeing the leaking purge valve to suck from the tank instead of sucking absorbed vapours from the purge cannister .... It would be nice to have newer one to swap it out for to confirm this tho.