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Doing the reverse drive south on 395, I filled up with no-ethanol 91 octane at the WalMart Supercenter in Gardnerville NV, and started the climb into the sierras with about the same conditions as the northbound trip: 90F+ temperatures, tank about 1-2 gallons below full. ? Absolutely no fumes or pressure this time, checked at 6000' and 8000' elevations. ? Gas temperature was about 115F, which is not quite as high as the 120F on the northbound trip.

On Jul 20, 2023, at 9:33 AM, monicact@... wrote:

To muddy (or hopefully maybe) clear the waters a little more:

I had my test of the spring breather bend/new gas cap last Sunday. Short version- it was mixed.

Longer version-

It's finally hot in Truckee/Tahoe. Drove around Truckee noonish with no problems (on mostly empty tank), no pressure build up. Put 6 gallons in tank for trip to Reno. No problems at all, including no pressure, in drive to Reno and driving around Reno which was very hot, and included a lot of parked with the engine running (dog). Leave Reno and fill tank, with Premium, at a Chevron, on the outside side of town. Again, after all that hot, hot driving around Reno when stopping to fill up, there was no pressurization. Then we pull the 80 back to Truckee with no missing/stumbling make 1 stop in Truckee and at the 2nd stop I smell heavy gas odor and have small engine miss/skip. Stop and tons of pressure in tank. I rebend the filler spring (not sure how far to bend it and am cautious about F'ing it up), Next couple days driving around are mixed- a little gas smell and a little pressure and very slight engine skip. It was fine yesterday on drive half way around Tahoe.

That's all I got, but I don't have anything consistent to point to except maybe the gas make-up and/or quality (which I have not been noting), combined with heat, and maybe at 4000' elevation. And maybe having a full tank.

David

On Thursday, July 20, 2023 at 08:19:59 AM PDT, Michael Diehr <md03@...> wrote:

More musings...

David and my experiences run in parallel:

- both driving 2000 EVCs up the 395

- filling up in small towns with Premium 91 octane

- having tremendous fume release with heat + altitude

- pressure is taking literally minutes to release all the fumes

But some notable differences

- David is reporting drivability issues: "Had a really hard time pulling up Sherwin summit on 395 and again up to Convict Lake."? My van drives fine.?

- David is having problems at 4000' elevation: "When I stopped for gas in Bishop the tank released pressure for about 10 minutes".? My van is fine at 4000' but I did have problems at 6000' and 7500' when hot (but not at 8200' when the gasoline was cold)

- My van has a brand new GM vapor canister retrofit, David's is presumably stock.

- My van has a brand new N80 and all lines are clear (not sure about David's)

- After venting, my van will immediately create more pressure with the engine running which stops when the engine is off (I don't think David tested this).

How to make sense of this:

- the root cause is the same - "bad" gasoline (E10, or perhaps E10 in a winter blend) + heat + altitude is boiling the gas on the round trip to the fuel pump, leading to a tremendous amount of vapor.

- in David's van, with the stock Vapor canister, the system gets quickly overwhelmed so he's venting at 4000'

- in my van, the new GM vapor canister does a better job, but eventually gets overwhelmed and vents at 6000'

- something is causing the N80 system to not work well, so not enough vapor is getting purged

Theory:

Gas is boiling on the round trip via the fuel pump.? We are both having some ECU issue, such as MAF or Oxygen sensor issues.? The van thinks the mixture is too rich, and therefore is keeping the N80 mostly closed.? So even though the N80 system is in good mechanical condition, it's not being commanded to work properly, and not enough vapor is getting purged.

I have a VCDS in the van - is there any way to test this theory?