Evap leak at breather on filler neck? Might have to dig deeper...

[RickHaleParker]

Great info! I'll try that today and see what I can find. It's gotta be one of the hoses above the tank that's leaking, since there is nothing else that I can find wrong here.

If you cannot find a leak in the tank system with smoke. Hook a vacuum pump to the same hose and see if it will hold a vacuum.
Don't forget to craw out from under and check for smoke at the gas cap.
My Smoke machine has a pressure gauge on it that measures back pressure. Does yours ?

[bmdubya1198]

No, I just have a pickle jar with a soldering iron epoxied to the lid, cover a sock in mineral oil and smoke! Janky but effective.
No leaks to be found anywhere in he system with smoke. This hose from the canister to get tank looks like it was pinched a little bit, but not enough to affect anything. Then again, who knows... these cars can be picky.

[RickHaleParker]

No, I just have a pickle jar with a soldering iron epoxied to the lid, cover a sock in mineral oil and smoke! Janky but effective.

You should of found something by now. That indicates there is something wrong with your test conditions.

Add a air pump to your smoke machine. To pick up and move the smoke. That way you have a higher air pressure on the inside of the leak. If the air pressure is the same on both sides of a leak it, the smoke will not pass through the leak. You need a pressure differential to force it through.

Everything flows from high density to low density. No work get done without a force. Elementary physics.

Keep in mind you may need to displace gallons of air in the tank before you will see smoke at one of the highest points.

[bmdubya1198]

I use a hand air pump on the smoke tester, and I can see smoke clearly pushing out when I disconnect that quick connect hose to the left that attaches to the canister hose. I didn't notice anything coming from the gas cap when I removed it, but I believe that's due to the fact that there's a check valve at the bottom of the filler neck. Or fuel may be blocking it due to the angle the tank is sitting... I can re-test for that theory.

It would be hard to pressurize it beyond that due to my setup.

[bmdubya1198]

Well, got the bright idea to pull the filler neck to replace the gasket, and when I did that, smoke started pouring out. I can confirm there are NO leaks. I don't know that the pressure sensor is bad, but who knows... this is getting annoying. I need to try to move canister to tank hose a little bit so it doesn't press against the body, but I'd like to see how it's routed on my S70. Unfortunately the weather is miserable right now, and it's a challenge to get outside and check that.
Anyway, I replaced the gasket on the filler neck anyway since I had it on the shelf, so that's halfway done. It's not easy to balance this tank alone and try to push the neck back in.

Update... I checked the S70 and the hose is routed exactly how I have it on the V70R. All I can think is that the tank expanded while it was sitting due to the gas fumes. Only reason it would be hitting the body.

[bmdubya1198]

Alright, everything is back together and it still fails the test. I continued through fault tracing on VIDA, and got to the point to apply pressure to the tank via the purge valve hose, after clamping off the J-hose to the close valve. Typically this test is supposed to be performed with a regulated 7 kpa, and I had to compromise because I don't have a pressure regulator that can go that low. Instead I used a hand pump and a vacuum gauge tee'd in. I tested it and it is totally sealed.
Once I hooked it up, the pressure did not hold. I believe this is because it takes time to build pressure in the fuel tank, since VIDA says to let it build pressure for 5 minutes. I didn't pump it for long, and when I pulled the hose off, there were strong gas fumes coming from the hose. So it's definitely building pressure, just not sure how quickly it should be able to do so.

[bmdubya1198]

Double checked for any block in the canister, we're good there. I cannot pull vacuum from any of the 3 ports. I'm going to double check the purge valve to canister hose, which I suspect COULD be the problem. I don't know what else it could be.

Interestingly, I can't find anything wrong visually on this graph, which I took yesterday after getting the car back together. The pressure seems to build, then bleed off quickly once the purge valve opens. I guess it's too quickly for the ECU.
I ran the same test on my S70, and it was a little different. Due to the scale differences, it looks different visually, but they seems to be similar data-wise. The CP and close valves are opening at different times on the V70, whereas the CP valve opens sooner on the S70. I don't know what this is supposed to mean.

V70R Test

test with other gas cap.png (31.81 KiB) Viewed 1397 times

S70 Test

S70 leak diagnostic.png (31.64 KiB) Viewed 1397 times

[bmdubya1198]

A user messaged me about a possible solution to this, and I realized I never posted a solution. I wish I had a solid answer as to what fixed the code, but this is just a guess. I believe the solution in this case was the purge valve, as that was the last thing I ended up replacing just to try to eliminate it as a cause. Turns out it may have been the cause.
As of today, the code has not returned.

[rrres]

Good update! My 99 had an intermittent P0455, which would clear after a couple of days or so. I tested the purge valve by jumping it with battery power and blowing or sucking on the corresponding port. It always passed that "bench" test. Then one day, the p0455 went on and would not go away. I made a homemade smoker and was ready to smoke the evap system...then I found a later model v70 at a junkyard that looked like the hoses coming off of the purge valve had been recently refreshed...The purge valve also looked new-ish so I grabbed it. Installed it and the P0455 hasn't returned. Not sure what was really happening but the "bench" test was making the old purge valve work during the test but in actual driving conditions, the purge valve was failing. (maybe something to do with weak voltage while running versus direct battery power during bench test)