EVAP system circumvention go or no go?

[Van Deütsch]

'84 Vanagon:
In a loooooonngg process of troubleshooting and elimination, I bypassed (disconnected) and plugged my charcoal canister and all associated hoses. I made sure those hoses that were running into the air box and back to the throttle body and plenum were plugged. I did this a while back while trying to figure out if the fuel tank had too high of a vacuum from the engine sucking through the carbon canister competing with the fuel pump sucking the other way. It sounded logical at the time....

Anyways does anyone know if this would affect the engine at all? As far as I can think of it is just a system to contain and send back to the engine evaporated fuel for emissions compliance. I am wondering if there is something I am missing here. Is that tiny little bit of air that flows through the pinhole restrictor in the vacuum tube to the throttle body required?? At this point it is just completely eliminated. I'll be re-instating again before I go to smog it. Any comments appreciated.

[Dogpilot]

It can, according to VW service bulletins cause rough running and bucking symptoms. Also, if the vent is plugged or the control valve does not work properly you will get a vacuum going in the tank and then the system pressure will drop.

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Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

[Van Deütsch]

At idle and HIGH vacuum, the throttle body vacuum line operates the valve into the closed position and eliminates the charcoal cannister circuit. At high speed and LOW vacuum the valve opens and the cannister vapors go to the plenum. That's my understanding. I can see if it were malfunctioning that it might affect driveability.
If it somehow opened the valve at idle, you'd have a vacuum leak symptom.

Since I've basically removed it, I am assuming it would not affect anything. I guess I'm looking for confirmation of that. I thought I may have overlooked something simple. I made sure the tank does have a generous vent via the hose that went to the cannister being open. It should now have no effect on the fuel tank or the vacuum lines and any running condition of the engine?

Hey Dogpilot -Are you and A&P tech? I'm in A&P school in Los Angeles.

THANK YOU FOR POSTING THOSE DIAGS.!

[Dogpilot]

To be honest, I have done what you describe, plugging the lines and such. It had no effect on the overall drivability. What does have an effect is a situation if the vent is plugged and the tank gets a vacuum. One of the drivability tests is to drive about without the gas cap for a while, since it takes time to suck all the air out of the tank. This does affect the way the engine responds, your fuel pressure starts to drop as a vacuum increases in the tank. Other than that, no, it is not a big issue.

I am an A&P and an IA, besides all the flying ratings. I own a large Repair Station and do heavy structurial repair and we are the field service reps for Turbopower's turbine engines (my mechs put on their shirts when we do their work). You are in a field that is shrinking. We have trouble finding labor all the time as people are retiring out of the industry. The skill of bending metal is becoming lost.
_________________
Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

[tencentlife]

[Dogpilot]

You know that weird running issue I had that turned out to be the spark plug wire. In the course of all that, I naturally called GoWesty, since my engine is on warrenty, to see if they, experts working on these all the time, could give me some other leads to test. One of the items he mentioned, and has actually seen was a vacuum being pulled in the tank. Ergo why he told me to drive around with the cap off.

On a lighter note, we just reskinned a Cessna 210 wing that buckeled from vacuum being pulled on the integral fuel tank from a wasp filling up the vent line. Only cost about $30,000 to fix. We also had to repair a Twin Otter aux tank system that had the same thing, not as much damage. It is funny, if you have a vent line blockage, the fuel pump suddenly becomes some kind of wonder device and pulls a nearly perfect vacuum. When in normal operations it barely puts out enough to start hot. The PT6 pump can actually pull such a good vacuum, it causes gasses to come out of solution in the fuel, causing engine cut outs from the gasses in the line.

In my case I noted no difference cap on or off. There is actually a VW service bulletin on this saying 'it effects drivability.' They do not elaborate.
_________________
Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

[tencentlife]

Yeah, "affects driveability" was always their catch-all for "we don't know what the F is up".

[Dogpilot]

Cavitation is also correct, however, this can happen all the way down the lines. Since jet fuel is actually an odd blend of kerosene and gasoline in varying percentages depending on the climate and use. It is one of the partial pressure things, the cavitation occurs at the pump gear or impeller face by localized low pressure areas (reducing the boiling point, as you said).

Some vent lines are screened some are not. There is a lightning strike issue with some of the vent lines, so they are not screened. On Twin Otters, for example, they have a guard that looks like half a soda can for lighting protection, and no screen. Screens also have a nasty tendancy to ice up and subsequently close off.

Weird insect story. On take off, I centered a small flying ant with the Pitot Tube (the airspeed indicator input). My airspeed went to zero at rotation. A disturbing time for this to happen. So I went around and landed. We looked in the pitot, and there looking back at us was the bug, still living. We fished him out with a small piece of safety wire and rocked on.
_________________
Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

[Van Deütsch]

Thanks all for the redux on the tank venting questions I had. It confirmed what I thought, basically not much effect unless cannister vent plugged with system hooked up or raw gas in cannister. I did not know there was a vent to the atmosphere on the bottom of the cannister. Makes sense though.
And yes, I get confused with which port on the TB gets vacuum on what side of the butterfly.

In regards to gas going to vapour at low pressure, I fought for a long time to get rid of a bubble of air in the clear tubing i had inline in front of the fuel pump. Never really solved that and it bugged me.

I'm actually in the sheet metal portion of training now and can't get enough lab time to satisfy me. I'd spend days there if they'd let me. I'm a sailplane pilot and absolute soaring nut. I find working on aircraft completely absorbing and a blast and approach it with a "craftsman" mentality and obligation to quality. Unfortunately, most all of the students in the program I attend I would not let work on my toilet much less my aircraft.

[Dogpilot]

If you think it is bad in school, try interviewing some of these blivits. Good sheet metal guys are born, not trained. They look at something like this and go "Oh Boy!"

_________________
Geology with a Syncro rocks!
86 Syncro Westy AKA "The Bughunter"
98 Disco I
08 Range Rover SC
08 VW Rabbit S
1951 O-1G

[tds3pete]

My charcoal cannister (79 2.0) had suffered some kind of "event" with the PO which left it scorched and my tail light housing melted.

I removed the system, left the tank venting to ambient, plugged all other lines, and see no effect on performance.
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'58 Westy camper-come and gone
'73 Westy-bought new in Holland,now gone
'86 Syncro weekender-come and gone
'79 Westy...Oscar
'95 Eurovan Camper/5 spd...Marsha Mellow

[tencentlife]

There shouldn't be any effect on engine performance, one way or another.

Emissions controls got a bad name with most folks as expensive, power-robbing additions imposed by EPA, and there was some truth in that, but EEC was the unknown emission control that has a very positive effect on smog formation, but is cheap, low or no-maintenance, and causes no power or mileage penalty whatsoever. It's just collecting and holding in an activated carbon matrix the fuel evaporate, rather than venting it to the atmosphere. When working, its effect on mixture is imperceptible, unless it's not working properly and is opening at idle, in which case idle mixture and steadiness can be affected. Also, under the same circumstances, hot restarting can become difficult. Most troubles any of us have with the system are the fault of the wear in our old throttle bodies, not any inherent flaw in the EEC system itself.

So if you unhook it, you'll see no effect on performance, and the same goes if it's hooked up and working properly. But if it's vented to atmosphere, you can feel good that you're making your own little contribution to more smog in your town.

[dhermanesq]

We basically took off all the evap stuff on this '87 westy and in my humble opinion, it worked better than before! I think though that Shelly had some other stuff going on with that piece-o-crap. BTW, no offense, but this thing was beyond any resto. There was sooooo much wrong and soooo much rust. It sho 'nuff fun to drive though. Good times.
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1993 VW Eurovan 5-Speed
1995 Mercedes S600 v12 (Rides again!)
2001 Passat V6-30v