Gas leak from tank line to carbon cannister

[sevvy]

Hi, Ive got a 1981 seville 6.4l in Australia, just bought car at auction. Gas leaking at cannister, I removed it plugged vac & carb lines left the tank line open. 4 min drive & gas is pumping out the line from tank. Tank level is nearly empty, there is pressure in tank when you remove cap. Have read a lot of forums on other vehicles with this prob, some ppl have tank lines swapped, could it be something else?? Any suggestions or anyone else dealt with this prob???

[The Tassie Devil(le)]

Welcome to Cadillac ownership.

Now you need to get a Shop Manual, as you will find you will be seeking information all the time.   If you don't have one, I have one here that I will sell to you for AU$50.00, plus postage from Tasmania.

Bruce.

[sevvy]

Thanks , It came with a Haynes & a heap of service spare parts

[35-709]

GET THE REAL CADILLAC SHOP MANUAL!!  Give the Haynes away or throw it out.

[TJ Hopland]

Haynes manuals can be handy if your parking spot isn't level, you may even be able to use 2 or 3 of em. 

Sounds like something isn't right.    The tank is theoretically sealed so all the venting is done through the canister.   Tank should have 3 fittings like most of the 70's and 80's did.   The largest one 3/8" is the fuel supply which in this case is under pressure from the in tank pump.  Its only like 13 psi so nothing too crazy.  The 1/4 is the return line from the regulator which is in the throttle body.  The 5/16 is the vent which runs to where ever the control solenoids are,  I can't remember if in 81 they are on the top of the canister or if they are up on the engine. 

Somewhere there are computer controlled solenoids that control what is happening with the venting.    When the engine is running engine vacuum is connected to the canister as is the tank.    The tank isn't under vacuum because the bottom of the canister is open so the engine vacuum is just sucking some fresh air past the charcoal and picking up any stored vapors along the way.   The tank can also 'breathe' at this point so it should not be under pressure or vacuum.  It can draw air in as the fuel level goes down through the canister or if the fuel expands with heat can expel air and vapors into the charcoal where it will be picked up by the engine.

There are conditions where it shuts off the vacuum from the engine and some have multiple levels of vacuum so they may open wider when you first start up then switch to a more minimal setting for cruising.   I don't remember what happens when you shut the car off.  I think one of the solenoids acts as a pressure relief valve so if pressure builds in the tank at some point it will allow it to vent where the vapors in theory get trapped by the charcoal and the 'air' gets expelled out the bottom of the canister. 

If something isn't right in the plumbing or with the solenoids the vent valve to the tank may not be getting opened when it should or is getting vacuum applied all the time.   Later systems got more complex  and they actually maintain either pressure or vacuum on the tank at all times and actually monitor it,   442 isn't just an Oldsmobile, its the nagging trouble code when the system isn't happy.   These systems are not that fancy so getting them working properly really should not be that difficult. 

I think the fittings at the tank are all different sizes so it would be difficult to mix them up but who knows it may be possible.    Typically the vent is in a baffle right at the top of the sending unit so the tank would have to be overfilled to get fuel into it    The return line is usually lower,  it may not be at the bottom but its at least 1/2 way down so if they did somehow swap them plus screwed up the plumbing up from so the tank got under pressure it certainly could force fuel down that line.   Having the return on the vent may not be noticeable except for maybe some noise of fuel dribbling if the pump was fairly quiet.   

[The Tassie Devil(le)]

Haynes manuals can be handy if your parking spot isn't level, you may even be able to use 2 or 3 of em.   

Love it.   Now, all I have to do is remember it.

Bruce.

[sevvy]

Plugged the leaking line for now & the car is running so much better, tank pressure seems about the same after driving although a hot day it may be different, had a look at the tank lines the return & vapour lines look close to same size & there was some old masking tape on them as tho they were marked & removed at some point. The pics I looked at online one line was 1/4 a lot smaller but mine doesn't appear to be without dropping the tank anyway. Im going to swap the other 2 lines as an experiment if I can this week. Still as you said it still shouldn't reach the return line with low fuel unless its a modified item, which as were in Australia maybe it was a modified off a different model??

[The Tassie Devil(le)]

If it was a RHD conversion, then the markings were probably done so that everything could be put back together following the reinstallation of all the parts.

There would be nothing different for Australia, unless someone had actually removed some of the anti-pollution stuff.

Bruce.

[sevvy]

It is RHD done by Chapel engineering so I believe from new & its all stock

[TJ Hopland]

Hopefully they didn't label them drivers side and passenger side and then do the conversion. 

Its possible the EFI changed the line sizes slightly but I thought I had worked on a later 80's that was still those 3 sizes.

[sevvy]

Swapped the 2 lines, they are slightly dif sizes but was possible, thought it had fixed it, as without the canister attached no fuel came out line. Refitted canister & 5 min drive fuel leaking again