Evap leak help please!
11-18-2014, 10:17 PM
#11
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OK, so here's what I'm thinking.
When the test begins, the LDP pressurizes the evap system, and the N80 closes, which traps the pressure between the LDP and the N80. Between these two parts are the charcoal canister, the fuel filler neck, the gas tank, the roll over valve, and all the lines running between them.
If I block off the line going from the charcoal canister to the filler neck, the test passes. This means that the LDP, the charcoal canister, and everything between them are fine.
With both lines to the N80 valve capped off, the test still fails. If there was a leak between the manifold and the LDP, it wouldn't be seen by the test, correct?
This isolates the leak to the filler neck, the gas tank, and the line running to the N80 valve.
There are 2 lines running from the back of the filler neck to what I assume is the gas tank. There's also a line running off the side of the charcoal canister, I believe this one goes to the N80 valve. Since it didn't leak when the canister was tested, I think this line is good as well.
This leaves just the filler neck and the gas tank. There's a strong smell of gasoline whenever the test runs, so I'm almost positive some part of the filler neck is leaking. What bothers me is that I pressure tested it off the car and the only part that leaked was the gas cap at around 1 PSI. I'm hoping that the pressure test generates more than that and the cap is the reason for the leak.
One strange thing I did notice is that when pressure and vacuum testing the 2 check valves between the N80 and the manifold, it wouldn't hold vacuum or pressure. I'm assuming those check valves are there to prevent pressure from flowing backwards from the manifold to the N80 under boost, in which case they should hold vacuum when tested correct? Either way, I don't see them causing the small evap leak, since the pressure should only stay between the LDP and the N80.
Sorry for the long rant, just thinking out loud and seeing if there are any flaws in my logic.
When the test begins, the LDP pressurizes the evap system, and the N80 closes, which traps the pressure between the LDP and the N80. Between these two parts are the charcoal canister, the fuel filler neck, the gas tank, the roll over valve, and all the lines running between them.
If I block off the line going from the charcoal canister to the filler neck, the test passes. This means that the LDP, the charcoal canister, and everything between them are fine.
With both lines to the N80 valve capped off, the test still fails. If there was a leak between the manifold and the LDP, it wouldn't be seen by the test, correct?
This isolates the leak to the filler neck, the gas tank, and the line running to the N80 valve.
There are 2 lines running from the back of the filler neck to what I assume is the gas tank. There's also a line running off the side of the charcoal canister, I believe this one goes to the N80 valve. Since it didn't leak when the canister was tested, I think this line is good as well.
This leaves just the filler neck and the gas tank. There's a strong smell of gasoline whenever the test runs, so I'm almost positive some part of the filler neck is leaking. What bothers me is that I pressure tested it off the car and the only part that leaked was the gas cap at around 1 PSI. I'm hoping that the pressure test generates more than that and the cap is the reason for the leak.
One strange thing I did notice is that when pressure and vacuum testing the 2 check valves between the N80 and the manifold, it wouldn't hold vacuum or pressure. I'm assuming those check valves are there to prevent pressure from flowing backwards from the manifold to the N80 under boost, in which case they should hold vacuum when tested correct? Either way, I don't see them causing the small evap leak, since the pressure should only stay between the LDP and the N80.
Sorry for the long rant, just thinking out loud and seeing if there are any flaws in my logic.
11-19-2014, 08:51 AM
#12
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I really hope it's not the same issue seen here:
quattroworld.com Forums: EVAP System: Large Leak Detected - SOLVED
Originally I didn't think it would be the tank since the smell was near the filler neck, but apparently that can happen from a tank leak as well.
Does anyone know where the N80 valve gets it's source line from? There are a lot of lines down there, and I can't account for all of them.
Would there be any safety issues if I installed a check valve on the line going from the charcoal canister to the filler neck, then plumbed the N80 straight to the charcoal canister? I'm thinking this would allow pressure from the filler and gas neck to flow into the charcoal canister as needed, but would block those parts off from the LDP test. The N80 would then get it's vapors directly from the charcoal canister and shouldn't throw an error.
This would be a temporary fix until I have time to repair the tank.
quattroworld.com Forums: EVAP System: Large Leak Detected - SOLVED
Originally I didn't think it would be the tank since the smell was near the filler neck, but apparently that can happen from a tank leak as well.
Does anyone know where the N80 valve gets it's source line from? There are a lot of lines down there, and I can't account for all of them.
Would there be any safety issues if I installed a check valve on the line going from the charcoal canister to the filler neck, then plumbed the N80 straight to the charcoal canister? I'm thinking this would allow pressure from the filler and gas neck to flow into the charcoal canister as needed, but would block those parts off from the LDP test. The N80 would then get it's vapors directly from the charcoal canister and shouldn't throw an error.
This would be a temporary fix until I have time to repair the tank.
Last edited by crono35; 11-19-2014 at 09:08 AM.
11-19-2014, 10:06 AM
#13
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I really hope it's not the same issue seen here:
quattroworld.com Forums: EVAP System: Large Leak Detected - SOLVED
Originally I didn't think it would be the tank since the smell was near the filler neck, but apparently that can happen from a tank leak as well.
Does anyone know where the N80 valve gets it's source line from? There are a lot of lines down there, and I can't account for all of them.
Would there be any safety issues if I installed a check valve on the line going from the charcoal canister to the filler neck, then plumbed the N80 straight to the charcoal canister? I'm thinking this would allow pressure from the filler and gas neck to flow into the charcoal canister as needed, but would block those parts off from the LDP test. The N80 would then get it's vapors directly from the charcoal canister and shouldn't throw an error.
This would be a temporary fix until I have time to repair the tank.
quattroworld.com Forums: EVAP System: Large Leak Detected - SOLVED
Originally I didn't think it would be the tank since the smell was near the filler neck, but apparently that can happen from a tank leak as well.
Does anyone know where the N80 valve gets it's source line from? There are a lot of lines down there, and I can't account for all of them.
Would there be any safety issues if I installed a check valve on the line going from the charcoal canister to the filler neck, then plumbed the N80 straight to the charcoal canister? I'm thinking this would allow pressure from the filler and gas neck to flow into the charcoal canister as needed, but would block those parts off from the LDP test. The N80 would then get it's vapors directly from the charcoal canister and shouldn't throw an error.
This would be a temporary fix until I have time to repair the tank.
11-19-2014, 12:02 PM
#14
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I'm not sure- I tried calling a dealer and asking and was put on hold for a long time, after which I haven't tried again.
I think i'm actually getting very close to the source. I replaced the gas cap and it definitely holds better now; after the test, when I remove the cap, there's an audible hiss where there wasn't one before. However there is another part leaking where all the hoses are on the filler neck. If i run the group 71 test then shut the car off after everything is pressurized, I can hear a leak in that general area. I think it was always leaking before, but the fact that I had the wrong cap on (1.8T cap off an a4) was masking the smaller leak.
I plan to pressurize the tank on the car to further narrow down the leak.
I think i'm actually getting very close to the source. I replaced the gas cap and it definitely holds better now; after the test, when I remove the cap, there's an audible hiss where there wasn't one before. However there is another part leaking where all the hoses are on the filler neck. If i run the group 71 test then shut the car off after everything is pressurized, I can hear a leak in that general area. I think it was always leaking before, but the fact that I had the wrong cap on (1.8T cap off an a4) was masking the smaller leak.
I plan to pressurize the tank on the car to further narrow down the leak.
11-19-2014, 01:08 PM
#15
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FYI, I found the leak. I had used some pep boys hose clamps on the line that attaches to the front of the filler neck. This wasn't holding. I think the plastic behind it is too thin to clamp down on... I'll try replacing this line with a similar sized rubber line.
With both side of that line plugged, the test passes. I am SO thankful it's not the tank.
With both side of that line plugged, the test passes. I am SO thankful it's not the tank.
11-20-2014, 05:59 AM
#16
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FYI, I found the leak. I had used some pep boys hose clamps on the line that attaches to the front of the filler neck. This wasn't holding. I think the plastic behind it is too thin to clamp down on... I'll try replacing this line with a similar sized rubber line.
With both side of that line plugged, the test passes. I am SO thankful it's not the tank.
With both side of that line plugged, the test passes. I am SO thankful it's not the tank.
Good luck!
11-20-2014, 07:34 AM
#17
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I fixed the line, but found that where the nipple attaches to the tank is leaking a bit. Not enough to fail the test though, so I'll fix that at a later date.
11-20-2014, 09:30 AM
#18
AudiWorld Super User
Don't use the audi-approved fix…I've read that it fails over time. There is a special adhesive and filler compound available from Tech-Bond IIRC for the HDPE(?) fuel tank.
11-20-2014, 01:16 PM
#19
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Yeah, I read that thread all the way through... I'll order some shortly. Luckily this leak is accessible with the filler neck still installed, but I don't know if gravity will be an issue.
