Gasoline Fumes when Hot & High

[xEVC]

For years, a number of us have been having issues where our Eurovans will vent copious amounts of gasoline fumes when driving at Altitude in Hot Weather.

We've been discussing this primarily over on Groups.io here: https://groups.io/g/eurovanupdate/topic/113184884

The fume venting problem is related to, but separate from, issues with being unable to fill up the gas tank.

I was having both problems, and after a complete rebuild of the Evap/N80 system, including retrofit of a GM vapor canister, the "unable to fill" problem is completely solved for me.

But the "hot & high" fume venting problem remains, though only happening for me in extreme conditions.

For example, in June I completed a 2000+ mile road trip up & down the west coast with zero problems.

But more recently, this happened:

Fill up with 91 octane at 4000' altitude, drove 60 miles. Temps were 95F+.
Drive up a steep grade (~15 miles) to 8000' altitude. Terrible venting of fumes. Fumes are coming from near the gas tank -- not the engine compartment, not the gas cap.

But, the problem is sporadic: The next day, drove back down from 8000' to 4000', back up to 8000', then back to 4000' then back to 8000', and had no fumes.

There is never any CEL or error codes in VCDS.

When I bought the van back over 15 years ago, it never happened. Over the years, it gradually worsened, even though my driving patten is unchanged (same routes, same gas stations, same climate).

Based on these experiences, here is my thinking:
* this is not an N80/Evap purge problem, as 99% of the time everything is normal.
* it's likely a problem one of the several hoses, valves, and lines in the gas tank evap/vent system
* it may be an intermittent problem (e.g. some valve is sticking open or closed) which explains my recent experience where repeated 4000' to 8000' trips gave different results)
* or it may be a problem with some combination of variables (kind of gasoline, temperature of gasoline, how full the tank is, ambient temperature, rate of altitude gain...)
* or it may be that the 1997-2000 Eurovan Evap system was always barely adequate, and changes in gasoline blends over the years (more Ethanol) have pushed it over the edge. Evidence for this: this problem seems most common in the 2000 model, the Evap system was redesigned in the 2001-2003 models, and it's my gut feeling that the problem is less likely when I'm running no ethanol gas.

What I've done:
* replaced all accessible parts (N80, Evap Canister, Gas cap)
* tested the hell out of everything (running VCDS while driving, watching the N80 duty cycle, etc.)
* smoke / leak tested various parts, and everything acts normal (at sea level and 70F temperatures at least)

What's next:

Drop the fuel tank and start replacing parts (valves, hose, etc.) However, none of these parts are available separately, so I'm wondering about simply buying an entire new (used) fuel tank and swapping the entire thing.

Is there a significant model year difference in the fuel tank?

Advice gladly accepted.
_________________
2000 Eurovan Camper (Winnebago)
Upgraded with 16" wheels

[gesoffen]

I've been following your troubleshooting efforts on Groups.io more out of curiosity than necessity.

If you are at the "drop the tank" stage of your troubleshooting efforts, I would consider a pre-emptive step of pressurizing the tank with low pressure air. As a pressure differential seems to be a significant part of this issue, pressurizing the tank in a controlled environment will allow you to check fittings, hoses, and even the tank itself. Leaking or venting air should be easy to hear but you could also use a soap solution and/or a hydrocarbon sniffer to help.

Good luck!
_________________
1973 VW Superbeetle (1302) w/ RAT 2270 T4
2003 VW Eurovan Weekender w/ 2.8L VR6 AXK, DYA 5 Spd Manual Conversion

[xEVC]

I have a smoke test machine and have run some tests, and as far as I can tell everything is normal - the tank holds pressure up to about 0.5 psi, at which point the Pressure Holding Valve opens and allows flow out of the line which goes to the carbon canister.

I'm doing these tests at sea level and ~75F temperatures, which doesn't prove much.

The idea of a hydrocarbon sniffer is an interesting one - when I'm venting, I can't isolate where the fumes are coming from exactly, which makes diagnosis difficult.

Edit to add: I can think of two possible, but different failure modes:

1. if the valve(s) leading from the tank to the carbon canister are sticking shut due to some weird altitude/pressure issue, then vapor pressure should be building up in the tank, until eventually some seal or hose starts leaking. I would expect the fumes to be coming from somewhere on the top of the tank where there are numerous connections.

2. if the valves are not sticking shut, but the gasoline is simply too hot and boiling (perhaps due to ethanol gas having higher RVP), then fumes would be heading to the carbon canister normally, but eventually overwhelming it, which would lead to fumes exiting the carbon canister vent line which eventually vents to inside the left side body frame.
_________________
2000 Eurovan Camper (Winnebago)
Upgraded with 16" wheels

[xEVC]

Here's a diagram of what I'm thinking.

1. If the Pressure Retention Valve (#21, Red Arrow) is sticking shut, then pressure will build up inside the tank, and eventually start leaking out from one of the tank fittings or hoses (red rectangle area) which are mostly located on top of the tank and impossible to get to. The solution here would be to drop the tank, and fix the individual part that's leaking, or else replace it or replace the entire tank.

2. If the PRV is fine, but the gasoline is simply vaporizing too fast, then the carbon canister (#23) will be overwhelmed, and vapors will exit the canister vent line (#5) and eventually pass out the green arrow (#17) which connects with the left side frame. The solution here is less clear - perhaps buying only non-ethanol gasoline in the summertime?

2.2.1 EVAP System, Engine Code AES
1 - Intake manifold
2 - Evaporative Emission (EVAP) Canister Purge Regulator Valve - N80
3 - Test connection
4 - Fuel rail with fuel injectors
5 - Ventilation line
6 - Check-valve
7 - Supply line
8 - Return line
9 - Ventilation line
10 - Transfer Fuel Pump (FP)
11 - Fuel tank
12 - Gravity valve
13 - Ventilation line
14 - Expansion tank
15 - Vent valve
16 - Cap
17 - Air filter for diagnostic pump
18 - Leak Detection Pump (LDP) - V144-
19 - Evaporative Emission (EVAP) Canister Purge Regulator Valve - N115-
20 - Vacuum line
21 - Pressure retention valve
22 - Hose coupling
23 - EVAP canister
_________________
2000 Eurovan Camper (Winnebago)
Upgraded with 16" wheels

[rocknroj]

Nice post xEVC!

Seems you know these systems well.. Perhaps some insight on the problem with my rig,

It is older (1993) and the problem is much more intermittent.

Not sure if my system is the same as your illustration.

It only happens under the following conditions.

Symptoms.. After a long drive to a high altitude campground. Waking up the following morning to some cold temperatures. Upon starting the engine there is a strong smell of fuel. It gets into the cabin and we must roll down the windows. Eventully after driving a few miles, the smell goes away and the symptoms disappear.

No issues filling the tank.

Only happens after a long drive from low to high elevation.

I had tried opening the fuel cap.. No obvious signs of pressure. No leaks or smells apparent in the engine compartment or under the car. No signs of leaks or damage to the vapor canister.
The n80 purge valve seems to be working correctly.
I have not tried to look at the top of the tank.

It only happens under the above circumstances. High altitude, parking after a long drive from a lower elevation. Only the following morning and only after starting the engine. Does not happen with extended stays at altitude.

I think I even tried opening the gas cap to check for pressure build up before starting the car in anticipation of the stink with no difference in behavior.

Of course these conditions are pretty hard to duplicate when one lives at sea level.

Penny for your thoughts.

[xEVC]

Interesting - I would guess your problem is not the same as mine - most of the symptoms are different, the 1993 EVAP system is vastly simpler than the 2000s, and the engine is different too.

You having fumes only on very cold start (at altitude) and the fumes getting into the cabin would make me wonder more about an fuel leak in the engine compartment - maybe the cold and low pressure atmosphere cause the injector o-ring to leak a bit, and the engine radiator fan is blowing the gas fumes around, and they are being sucked into the van via the fresh air vents? I would test this out by making sure the vent fan is off, starting the engine for a few seconds, and then sniffing around to see if there's gas in the engine compartment.

Note: I believe the 12 and 24 valve VR6 engines start up in a mode where they run quite rich and run the SAI pump to try to heat up the catalytic converter. My van smells quite gassy for a minute or so after cold start, at all altitudes, but those fumes are coming only from the tailpipe.
_________________
2000 Eurovan Camper (Winnebago)
Upgraded with 16" wheels

[shirk]

We have a 2001 and just this weekend have experienced this same issue.

This trip we drove from home in Vancouver up to Silver Star above Vernon BC, just as we were getting up near the resort climbing a steepish grade in rather hot weather we noticed a very strong fuel smell in the cabin.

Driving back home ascending out of Kelowna when topping out near the top again in very hot temps we noticed the fuel smell.

Our van doesn't sit for more than a week at a time, very little use during the week but used near every weekend for some road trip.

No issues with previous trips in hot summer weather over any of the mountain passes in BC.

My first step will be to inspect / replace all evap lines under the hood.

[xEVC]

Interesting that you are having a similar problem in your 2001.

Can you figure out where the fumes are coming from? Smelling them in the cabin could suggest they are coming more from the engine compartment rather than around the tank itself?

There's a long thread here about someone with a 2003 who had bad fumes, determined finally to be