Evap Leak Assistance - Interpreting Smoke Test

[big greasy taco]

I have been chasing an evap leak on one of the M3's. I did a evap system smoke test today to look for the leak. when I pressurized the system I found smoke pouring out of an open hose behind the passenger side rear fender liner, just below the fuel filler tube. Real OEM says that hose is a "vent" and shows nothing connected to it. My understanding was that the system is a closed loop when the gas cap is on, and there should be no leaks anywhere. yet that hose is called a vent and nothing should be connected. Can anyone help me interpret these results?

[George Hill]

Where are you pressurizing from, the gas cap?

You need to pressurize from the vent hose.

OR cap the vent hose and pressurize the line going INTO the purge valve.

There has to be some open to the atmosphere vent otherwise the fuel pump would pull a vacuum on the tank when running.

The DMTL pump closes off the vent line when running its system test.

[big greasy taco]

Not sure why the picture didnt post originally. The circled piece is the vent line smoke is coming out of

[big greasy taco]

Where are you pressurizing from, the gas cap?

You need to pressurize from the vent hose.

OR cap the vent hose and pressurize the line going INTO the purge valve.

There has to be some open to the atmosphere vent otherwise the fuel pump would pull a vacuum on the tank when running.

The DMTL pump closes off the vent line when running its system test.

I was pressurizing from the line going to the purge valve under the intake. The vent line was the only leak i visibly noticed leaking (and there is definitely a leak somewhere as i smell fuel and i get a gas cap loose code)

[George Hill]

I was pressurizing from the line going to the purge valve under the intake. The vent line was the only leak i visibly noticed leaking (and there is definitely a leak somewhere as i smell fuel and i get a gas cap loose code)

At this point I would plug that vent hose and smoke it again. If you can't find a leak then possible your purge valve is the issue.

If you were starting from scratch I would have smoked it from the vent hose that way you haven't disturbed the purge valve location.

[big greasy taco]

At this point I would plug that vent hose and smoke it again. If you can't find a leak then possible your purge valve is the issue.

If you were starting from scratch I would have smoked it from the vent hose that way you haven't disturbed the purge valve location.

the purge valve (under the intake manifold) is new. I replaced that already hoping it was the issue (it wasnt). Is it possible the "leak diagnosis pump" (#13 in the part diagram) is somehow faulty and allowing a leak?

[George Hill]

the purge valve (under the intake manifold) is new. I replaced that already hoping it was the issue (it wasnt). Is it possible the "leak diagnosis pump" (#13 in the part diagram) is somehow faulty and allowing a leak?

New doesn't mean good, seen it plenty of times. BUT purge valves rarely leak in my experience.

I would be surprised if its the DMTL pump, have you run the system test? What were the results?

[big greasy taco]

ok, I sealed off that vent valve and re-smoked the system. Significant amount of smoke coming from above the fuel tank (video link below). I am no expert on EVAP systems, but that doesnt seem like it should be leaking from up there

https://youtube.com/shorts/ntXcS_n9pPQ?si=3E8dsU4OTz1WeQqG

[kaiv]

Pop off the two access panels below the rear seat bench and go from there?

[big greasy taco]

Pop off the two access panels below the rear seat bench and go from there?

Hey Kevin, hope all is well!

That is my next step. I know there are a few vent lines up there, one of them has got to be leaking.

[George Hill]

Yes, as Kaiv noted I'd pop the passenger side cover off and take a look. Has the fuel pump been replaced recently? Sometimes they don't get installed properly and that will cause the leak, but generally it leaks gas too.

The vent lines up there aren't really "serviceable" so unless someone has had the tank out and didn't put it back together correctly you might have had some creature get in there and gnaw on the lines (see that all the time).