Thanks Mountainman, how would we go about checking the venting system, never did this before.

 

No idea. I've never done it. I think one is in the filler pipe, and the other is on the tank. They have valves and lead to a charcoal canister. I've seen people use their mouth to blow through the lines to check them. That's all I know.

 

the tank vents thru the evap cannister, vent solenoid and vent filter during filling and when the pump is running. when filling air is pushed out the vent line. when the fuel pump pumping fuel...air is drawn into the tank to keep it from collapsing. since you don't have a filling problem...I assume it must also be clear for air to enter when running. since you don't have a check engine light I assume the evap monitors are running and passing.

if you had a pressure or vacuum issue; I think you would hear something when the cap is removed...ie vacuum or pressure release.

 

vapours need to vent even when not filling, right. If the ambient temperature rises, the gasoline vapor pressure will increase in the tank too. (we've all seen jerry cans balloon out on hot days)

 

Years back when I lived in the city during one of those useless by-yearly Ontario mandatory Emission tests , I was told I needed a new gas cap to pass the test and the mechanic took the time to explain to me how the system works in my '03 Astro

Up to the Astro all my previous GMs have all been and still are all carburated so I had no idea that the Astro system is pressurized
in order to prevent fumes from escaping into the atmosphere

I was forced to spend $30 on a brand new and nice looking cap that did not come with the short plastic tab
that my original has that keeps it attached to the gas door while I'm refuelling

Passed the test and when I got home I put back the original cap , keeping the new cap to install only on the day of my
next Emission test ....ehehe

Useless Emission test ?

When we moved to northern Ontario I discovered that those tests are NOT mandatory in low populated areas in Ontario
but only for city slickers that live in one end of the city and go to work on the totally opposite end every day of the year ....ehehe

It kind of seems obvious that the after market 'third party' new caps used by the OP are probably restricted in the venting hole
creating negative pressure on the system
If it's possible to see the small venting hole in the cap it might be possible to enlarge it so that pressure does not build up
while the van is running , and if the trick works I would be very interested in some feed back

Thank you ...... Vinny in northern Ontario Canada

 

Thanks Vinman for the suggestion, you don't sound too sad to have left the city behind you, we left a long long time ago BUT turns out we were just on the borderline of having to get the E Test done (5 miles up the road it was not required - go figure). Not sure what to say about this gas cap problem because it seems to be OK now, a bit hard to get off sometimes but we live with it. Our last van was an 03 Safari AWD, had a lot of problems there with the AWD but finally just disconnected it. Good old vans!

 

vehicles with modern evaporative system (yes a 2003 is modern) do not vent thru the cap...they vent thru the evap cannister. if it vented thru the cap hydro carbons would escape to atmosphere defeating the purpose of the evaporative emission system.

 

North Bay altitude is far enough from T.O. , we get to spend our winters in the forest behind the house
I took a look at that new cap I've never used and I think it's got a thin film of white
lithium grease on the upper threads
Lubing it will make it easier to remove .....ehehehe

Cheers ...... Vinny

 

Thanks Vinny, gonna try the lube