开云体育On Apr 4, 2023, at 11:24 AM, Duane <txpigeon@...> wrote: The idea that the EVAP system is malfunctioning is very logical and I'm not ruling it out, but I am leaning towards other explanations. Pressure release / vent failure? Pressure increases the boiling temperature for all liquids - so if the gasoline in the tank is boiling, it's actually not under enough pressure. (Or, it's just way too hot)? The EVAP system has a LDP (leak detection pump), and although it's vacuum operated, it tests for leaks by holding a positive pressure. ? In my van there are no LDP codes in normal operation, but I've accidentally triggered the "small leak" and "large leak" codes when I was messing around, which leads me to believe the LDP is working, and my system is tight. I believe in the Eurovan the LDP is dual purpose, and is also the vent. ?From the same guide:?
I'm not clear what happens if the system gets over pressured - does the LDP vent have some sort of safety blowoff valve? ?Could that blowoff valve have failed somehow? ? Capacity Logically, the evap system does not have infinite capacity to deal with vapor. For example, the evap guide you referenced says: A 1% concentration of fuel vapor from the EVAP Canister can vary the air/fuel mixture by as much as 20%. This can have a drastic effect on engine driveability and vehicle emissions. I think it's quite possible that this system has a limit, and there is some combination of heat, altitude, and gasoline volatility which could overwhelm the system, so the purge can't keep up, and eventually the pressure is released, even if the system is 100% functional as designed. ?? Under this theory, VW designed the 1997-2000 evap system to handle "normal" conditions, but gasoline changes in the last decade were not something they planned for. As I say, I'm not sure of any of this, just trying to get more data and see what theories fit the evidence... |
