348 vapor canister purge valve removal

Well, now at least you don't have to worry about further tank collapse, but if it was my car, I'd be pretty darn curious how it is that there is postive pressure in my gas tank. Where would that come from? The gas is being pulled out via the fuel pumps. The manilfold is drawing vacuum. I don't get it. Did you install a turbo when nobody was looking?

 

Fuel and fuel vapors expand when heated. Hot engines heat up fuel tanks via heat soaking. The expanded vapors rush out when you open the gas cap to a hot fuel tank.

So if vapors rush out when you open your gas cap on a hot engine at a gas station, then all is normal.

But if outside air rushes *in* past your fuel cap instead...then you need to check for a problem with your fuel tank venting (e.g. fuel vapor canister and purge valves).

 

Yes, they do, but the whole point of the "Cannister" is to provide a vent for said vapors. Of course you could just drill a tiny hole in your gas cap, and that is how all cars used to work, but the cannister is supposed to be a better idea. The vapors are supposed to vent through the cannister with the activated charcoal absorbing any gasoline. I can imagine that the cannister would function optimally if it semi-restricted the venting so as to get a good exposure of the fumes to the charcoal, but I would not expect any actually detectable pressure. I mean detectable by a noise when the cap is opened. So my conclusion is that the cannister is due for replacement. After all if pressure is "whooshing" out when you open the tank, so are a lot of fumes. That hardly sounds like the intended outcome of a properly functioning anti-fume system. Otherwise, just plug the hoses going to the valves, and yank the hose going to the tank off the cannister. Voila! just like the good old days when men were men and fumes were for breathing.

I guess I need to shut up and tear mine up to really have a good look at it. Weekend after next. I will report here what I discover.

 

Great work, Ernie!! And a milion thanks, as, yes, I am stuck on the cannister. Thanks to you I can probably now get one for a very reasonable price. I love this site!

 

Yeah buddy!

 

I was just reading on a Jaguar site about a guy who cleaned his canister with brake cleaner, rinsed it out a few times and his idle got smoother. Hmm...

I have a feeling that one or both of my valves are starting to go, as well as my canister is semi-plugged. Looking forward to tearing it all up and seeing the gritty details. I need to get a vacuum pump and guage.

 

There seems to be a bit of confusion about how this system works. Let me clarify. The tank filler cap is sealed. The tank vents through a series of pipes to the valve mounted in the line to the top of the canister. This valve is a 2 way valve which will pressurise the tank to a small positive pressure as fuel heats and expands/vapourises. When the tank reaches the venting pressure it opens and allows excess pressure to vent to the atmosphere via the canister. The actual vent is on the top of the canister. Fuel is absorbed by the charcoal filter. If the pressure in the tank drops below atmospheric, the valve will allow air, from the vent on the top of the canister to go back into the tank to prevent it collapsing. This part of the system, the vent side, is completely automatic and independent of the electric valves. It will allow expansion and contraction while the car is not in use. As long as the charcoal does not become saturated, no fuel will escape to the atmosphere. It also operates automatically when the engine is running.

The other side of the system is operational only when the engine is running and is to regenerate the charcoal filter and remove the fuel absorbed. The 2 electric valves are to control the amount of air passing through the system so as not to upset the mixture. The valves are normally open. The ecu decides when to open and shut them depending on engine conditions. When open, air is drawn from the atmosphere via the vent, not the tank, through the charcoal and into the engine to be burned. This side is independent of the vent from the tank and even if the valves stick open, no vacuum is ever applied to the tank from the manifold. The only symptom would be slightly lean tickover. Provided the charcoal is adequately dried it will be ready to work next time the car is stopped. In my opinion Ernie's problem was a blockage in the vent part of the system, possibly in the canister, more likely the valve. Ernie's dud valve did not cause his tank collapse. It wont have been helping his smooth running though. My guess is removing the canister unstuck the valve by disturbing it.

Hope this helps.

 

For clarity the last sentence of above post should read :

"My guess is removing the canister unstuck the VENT valve by disturbing it."

It occurs to me, if Ernie blew his tank back out through this valve that could have cleared it.

By the way. With low utilisation, The tank will breathe a lot while standing idle. The charcoal will eventually get saturated. There will be insufficient air flow to regenerate the charcoal while the engine is running if only used briefly. The charcoal remains saturated. Fuel smells result.

The solution. Use your car more.

I get fuel smells yet I know there is no leak. I may try leaving a vacuum pump running on the canister for a couple of days to see if it helps. I'll post back here if I get round to trying it.

 

Thanks for that clarification. Your explantion lines up with what I have read about how these systems work in general. The only thing I was unaware of was the 2-way valve to limit varpor transfer to the atmosphere.

So perhaps a good soaking w/ brake cleaner will keep the 2-way valve from getting stuck? I am starting to think that for $200 I should just get a new can w/ a fresh valve. (And then not let 'er sit!! )

Also, perhaps my bit of negative pressure at re-fueling is normal as the 2-way valve is doing its job?

Finally, when the engine is shut off, the electric valves to the manifold are shut, or open? And what are the approximate parameters of when they are open and shut while the engine is running?

The more I try to imagine how the 2-way valve is connected, the more I want to get a new can so I can tear my old one up and see exaclty how it works!

 

Found this floating about the ether...
Image Unavailable, Please Login

 

Hi Randy, You are right. A degree of vacuum is not out of the question if you check it soon after starting or on a cold morning The 2 way valve allows a degree of expansion/contraction before it vents to reduce emissions. Under normal circumstances, by the time you have driven to the gas station the tank is hot enough to be positively pressurised-hence the whoosh on removing the cap. Initially, on starting up, negative pressure will develop as fuel is drawn from the tank - until it heats enough to vapourise fuel. The valve makes sure the tank is not damaged by either positive or negative pressure.

The valve is not in the can. Its in the line between the can and the tank, mounted on a bracket above the wheel arch next to the can.

The electric valves are passively shut when off but a slight vacuum will open them. When energised they are firmly shut. Not sure of the exact parameters Ferrari use to control them but they are usually shut(energised) at idle. The flow of air above tickover is pulse modulated to not upset smooth running of the engine.


Hope this helps
Phil.

edit Re: Putting air in tanks. Potentially hazardous if there is a source of ignition. Years ago when working with alloy fuel tanks we used to weld cracks with fuel still in the tank in after purging it with exhaust gas. I dont think the health and safety police would be too happy with this now!!

 

Great work ernie!
Does the QVs have this little bastard?

 

Thanks Phil! I need to check my "Whoosh". I get it at the gas station, but am not sure if it is positive or negative.

"Slight vacuum" on which side of the solenoid valve? The canister side or the manifold side? (I would guess manifold side, since I still don't see how you could have a vacuum in the canister as it is vented to atmosphere. Unless it was plugged up?)

So, with the 2-way valve between the tank and the can, I supose that one could clean the can by flushing with brake cleaner, flush the 2-way seperately and then test them both with a vacuum pump for plugged up/non-function.

 

The roll over valve is the one that 348pilot calls the 2 way valve. That is precisely what he is saying Ernie. That said valve must have been stuck - when you blew out your fuel tank with air, you unstuck it. Clearly if that valve was stuck, your fuel pump could crush your tank by pulling fuel out of it.

The purpose of the solenoids is to modulate the enrichment of the fuel-air charge that happens when fuel laden air from the canister is drawn in the intake manifold. The way this works is that the solenoids only open when two things are true, 1. The engine is off idle. 2. The engine is not wide open, i.e. it is operating in closed-loop mode. Why condition 2? Because as long as the engine is operating in closed-loop mode, the O2 sensor will detect any additional fuel being pulled from the EVAP canister, and, in real time, adjust the mixture accordingly.

Even if they were both stuck wide open you would not get any large vacuum in the tank unless your charcoal canister was pretty severely plugged. I strongly doubt that was or is the case, but I suppose it could be true. Point being, if you are still convinced that the faulty valves were to blame for the tank deformation, you would be well advised to check your EVAP tank for plugged condition. No?

On the other hand, what parts wizard amongst us has a line on a reasonably priced roll-over, anti turn-over, or 2-way valve? Whatever you call it, that little bugger could wreck some real havoc if it was stuck...

 

Here. http://www.delorean.com/store/p-6703-roll-over-valve.aspx

You have to "dust" it off a bit...

 

Great thread Ernie, and important thread. My canister is whacked and needing replacment, but I am CERTAINLY going to put an in-line filter on the canister's exhaust port as those granuals do [ ] get into the intake ports on the engine. Better check that out before damage occurs there too.

 

What makes you say its bad?

 

Seems to have nothing inside it, vacant/empty.

 

My postings on this canister and related is just more for general knowledge: so, you mention the ECU makes adjustments.

Being such, would removing or replacing the canister with an inline gas filter [I know, but this is just my idea] cause the ECU to be making incorrect adjustments?

I'm thinking it would be ok.