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Re: Eurovan Gasoline Fumes when Hot & High - Recap

 

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On May 7, 2023, at 2:25 PM, rmartin1962@... wrote:

This video is helpful in understanding evap system operation. https://youtu.be/y4heTf4rz7A

The video begins by describing the pre-1998 systems, which are simpler than our vans, and missing quite a few parts.

However, at 24.5 minutes it introduces the?Onboard Refueling Vapor Recovery (ORVR) system.
Link: ?Link https://youtu.be/y4heTf4rz7A?t=1483

Staring in 1998, the ORVR system adds some new parts:

Filler Breather Bottle
Pressure Holding Valve
Various tubes to connect

My rough transcription from the video:

During normal operation, the ORVR works the same as previous systems. ?Fuel vapors are collected in both bottles, then routed through the breather valve, then to the rollover valve, then on to the pressure-holding valve (PHV). ?The pressure-holding valve controls the amount of fuel tank pressure by keeping a small amount of pressure on the fuel in the fuel tank, so that fewer vapors are formed. ?When the tank pressure gets high enough, the PHV opens, allowing vapors to reach the evap canister. ? The PHV also allows air from the evap canister vent into the fuel tank to relieve the vacuum created in the fuel tank as fuel is pumped to the engine.

When the evap purge (N-80) is open, the PHV will close, preventing fuel vapor from being drawn directly out of the tank.

During refueling, the nozzle from the gas pump pushes aside the fuel tank filler flap, which pushes on the breather valve, closing the path from the operating breather bottle, trapping air in the breather bottle and and the top of fuel tank, to allow for expansion. ?At the same time, the larger vent line from the filler breather bottle is opened. ?Vapors from refueling will be forced from the tank, into the filler breather bottle, and on to the evap canister.

Based on this added complexity, I can imagine a few failure modes:

A. what if the breather valve doesn't open, or doesn't open fully??
This could cause the symptoms seen by Gary and Don: fumes from the tank would be blocked or restricted in reaching the evap canister. ?Bending the metal part in the filler neck so that the gas cap more fully opens the breather valve would be the solution.

B. what if the pressure-holding valve does not open at the right pressure, or does not open fully?
This might cause similar symptoms, as the path to the evap canister would be restricted or blocked. ? Fixing this would probably require dropping the fuel tank?

C. what if the valve to the filler breather bottle does not close? ?
I'm less sure about this scenario. ?The filler breather bottle pathway is normally closed, so having this one fail open would actually create an additional path from the tank to the evap canister. ?This would seem to be the opposite of what we are seeing. ?However, this additional path also bypasses the pressure-holding-valve, which could leave the tank at a lower pressure, which could lead to increased fume generation overall, which might be expected to make the symptoms worse? ?
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