Exterior Fuel Smell - Only Occurs With Full Tank

[A4orce84]

Hello Everyone,

Another day another issue with the B6 it seems. #B6Life

All the details on my latest issue are below:
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Car Background:
2004.5 Audi A4 1.8T Quattro with nearly 200K miles. I live in Austin, TX (warm climate) and the car is daily-driven. Just recently changed out thermostat, water-pump, and performed a coolant flush to resolve a coolant leak I had over the winter. Also, replaced alternator and a few other odds and ends recently. Overall, car has been running fine.....for about a month until this new issue started.


The Issue:
I currently have a slight odor of gas in the garage AND in the interior of the car after I fill-up with a FULL tank of gas. It appears to be coming from the rear driver's side area (close to the rear driver's side wheel well area) where I can slightly smell it. The smell starts to fade as I get closer to the 3/4 and 1/2 mark on the fuel gauge (the more I drive the car).

To assist in the troubleshooting, I have noted the following so far:
-Slight gas smell after I fill-up and have a full tank of gas.
-No CEL for gas light.
-Able to fill-up without issue (gas pump does not click-off or stop intermittently).
-Smell fades as it gets close to the 3/4 mark on the fuel gauge.
-N80 Valve replaced in September 2017.
-Fuel Filter replaced in April/May 2016.
-Fuel Pump Seals REPLACED (Drivers and Passenger side) in May 2018.


Possible Cause:
Doing some searching I've found a few posts on the subject. Specifically the following:
1. https://www.audizine.com/forum/showt...when-full-tank
2. http://www.audizine.com/forum/showth...ses-LDP-itself
3. https://www.audizine.com/forum/showt...n-tank-is-full

It sounds like it could be a leak somewhere, but my symptoms above don't really match anything like those connected to the evap system or charcoal canister so far.
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If I can provide any additional details from my end to assist in the troubleshooting process, please let me know. If anyone has any ideas / feedback / thoughts /etc. on what the possible root-cause of the issue is, it would be greatly appreciated!

Thanks,
Asif

[Let it snow]

The first link you posted mentioned a leak at the seal where the fuel pump drops in the tank. Have you investigated that? It is fairly easy to check both top seals on the Quattro tank.

[A4orce84]

The first link you posted mentioned a leak at the seal where the fuel pump drops in the tank. Have you investigated that? It is fairly easy to check both top seals on the Quattro tank.

Not yet! I will soon, but wanted to make my post and get all the information out there first.

[A4orce84]

Hey Everyone,

I just wanted to provide a mini update with this issue! I ended up replacing the driver's side fuel tank seal with a new one, and the gas smell has decreased about 70-80% when I have a full tank of gas currently. However, there is still a very small smell (20-30%) when I have a full tank, and I am unsure what else it could be. Doing the "sniff" test, I feel like the smell is still coming from the driver's side rear door area (near the fuel tank).

Question:
Besides the rear driver's side fuel tank seal, would there be any other items that would lead to the smell of gas when I have a full tank? Again, it is very faint compared to before, but it is still there unfortunately.

Thank you in advance to everyone for your time and help, it is greatly appreciated!

Thanks,
Asif

[alimo20]

As a note of caution - I had to order 3 different seals and re-do the install at least twice to get it right. I wound the seal around the fuel pump lid and then forced it, evenly, to sit 100% flush with the lip of the opening. it was not trivial. I would revisit that if you are continue to get leaks.

besides a crack in the tank or pin hole somewhere I can't think of something else. Is there a UV dye you can use in the fuel system?

[shurur9]

As a note of caution - I had to order 3 different seals and re-do the install at least twice to get it right. I wound the seal around the fuel pump lid and then forced it, evenly, to sit 100% flush with the lip of the opening. it was not trivial. I would revisit that if you are continue to get leaks.

besides a crack in the tank or pin hole somewhere I can't think of something else. Is there a UV dye you can use in the fuel system?

i always had better luck placing the seal at the tank opening and pressing the plastic cover on.
But either way, it can be tricky and certainly not trivial..a definite PITA.

I also buy new gaskets when ever I replace the sender units on either side, as the gaskets seem to get stretched or expanded from being exposed to the gas fumes.


I use coffee grounds inside the car to suck up the gas smell

[A4orce84]

Hello Everyone,

So, both driver's side + passenger side tank seals have been replaced. Both seals have been installed correctly, and there are no issues with how they are seated. However, as, I said in my last post, I am still getting a slight fuel smell from what seems to be the rear driver's side area of the car. It is a much much less smell compared to when the driver's side seal was leaking, but I am still getting a slight smell when I have a full tank of gas.

Question:
What other components of our fuel system would lead to a slight gas smell with a full tank?

Thanks in advance for everyone's time and help, it is super appreciated! =)

[projectvoltron]

I had to replace the entire fuel sending unit on my 05 3.0. The Plastic section at the top had a tiny hairline crack in it and fuel would only come out and stink with a full tank.

Just me .02

[A4orce84]

I had to replace the entire fuel sending unit on my 05 3.0. The Plastic section at the top had a tiny hairline crack in it and fuel would only come out and stink with a full tank.

Just me .02

Is that something that is easy to visually check? (When the tank is not full obviously).

Thanks!

[projectvoltron]

Is that something that is easy to visually check? (When the tank is not full obviously).

Thanks!

Its probably easier with a full tank. I wouldn't have even noticed the crack if when I wiped the white plastic lid dry and seen a little bit of fuel leak out.

It was easy for me to diagnose and surprisingly easy to fix also.

[A4orce84]

Thanks @projectvoltron, will investigate this soon!

So, I realized I need to update a few details with the problem description in my original post. I updated it, but also pasting the main details again below for ease:

Problem Description:
I currently have a slight odor of gas in the garage AND in the interior of the car after I fill-up with a FULL tank of gas. It appears to be coming from the rear driver's side area (close to the rear driver's side wheel) where I can slightly smell it. The smell starts to fade as I get closer to the 3/4 and 1/2 mark on the fuel gauge (the more I drive the car).

To assist in the troubleshooting, I have noted the following so far:
-Slight gas smell after I fill-up and have a full tank of gas.
-No CEL for gas light.
-Able to fill-up without issue (gas pump does not click-off or stop intermittently).
-Smell fades as it gets close to the 3/4 mark on the fuel gauge.
-N80 Valve replaced in September 2017.
-Fuel Filter replaced in April/May 2016.
-Fuel Pump Seals REPLACED (Drivers and Passenger side) in May 2018.

Besides the possibility of a crack in the fuel sending unit, is there any other components areas where a slight gas odor would be emitting from?

Thanks again everyone, all of your time and help is greatly appreciated!

[old guy]

When the engine is turned off the LDP (Leak Detection Pump) located in the drivers side rear wheel well opens up a vent to atmosphere to relieve any pressure build up in the gas tank. The expanding fumes in the gas tank get pushed out through the charcoal canister, scrubbed, and exit through the LDP vent. If the charcoal canister is defective the unscrubbed fumes exit from the LDP vent resulting in the smell of raw gasoline. This video is pretty long but it gives a really good explaination as to how the evaporative emission system works.

[A4orce84]

Thanks Fletcher! If I understand you correctly, wouldn't I have this issue even with a low tank of gas then? Gas fumes are pushed through the charcoal canister and LDP no matter what level of gas that is in the tank, correct? Also, doing some googling, wouldn't a CEL be triggered if the charcoal canister fails? I guess I'm still trying to understand why the car itself thinks everything is fine, when in reality, it is not.

Thoughts?

[old guy]

You will get a CEL if the canister is clogged. When the ECM starts the N80 evap purge cycle it expects to see a slight change in the A/F ratio. It there is no change it assumes no air flow, thus the canister is clogged. What it can't do is to determine the efficiency of the canisters scrubbing ability. As long as it registers a change in A/F it assumes the canister is good.

One possible explanation for your issue: When you fill your tank from empty you displace a lot of air laden with gas fumes through the canister and out through the LDP vent. This loads up the charcoal in the canister. If the charcoal is fully saturated it can no longer scrub any more fumes and thus you get the gas smell from the LDP vent in the rear drivers side wheel well.

Once you begin driving the ECM starts the evap purge cycle. The LDP vent opens, thus allowing the N80 evap purge valve to pull fresh air in through the LDP vent. This air flows through the canister and allows the charcoal to release the stored hydrocarbon fumes. As long as you aren't refilling the tank the scrubbing that occurs when you turn the engine off is considerably less and the partially compromised canister is able to keep up with the fume load.

[A4orce84]

Hello Everyone,

So a few weeks ago Mr. Matt Devo helped me replace the charcoal canister on my car. UNFORTUNATELY, the gas smell still exists on a full-tank with my car and it still appears to be coming from the driver's side rear wheel well area. I've updated the troubleshooting list below with the charcoal canister info:

----
To assist in the troubleshooting, I have noted the following so far:
-Slight gas smell after I fill-up and have a full tank of gas.
-No CEL for gas light.
-Able to fill-up without issue (gas pump does not click-off or stop intermittently).
-Smell fades as it gets close to the 3/4 mark on the fuel gauge.
-N80 Valve replaced in September 2017.
-Fuel Filter replaced in April/May 2016.
-Fuel Pump Seals REPLACED (Drivers and Passenger side) in May 2018.
-Charcoal Canister REPLACED in July 2018.
----

When we replaced the charcoal canister, I did not see any torn lines or anything. It also might be worth mentioning, that last few fill-ups, if I don't fill all the way to a ful-tank (for example if I only put 5-7 gallons in the car) the gas smell does NOT exist. Only when I fill-up to a full tank does the issue rear it's head. At this point, I am at a loss on what the root-cause might be.

If anyone can assist in offering any advice / feedback on where the problem might be, it wold be greatly appreciated. Thanks in advance for everyone's time and help. It is greatly appreciated!

[caluma4x4]

My thoughts from that are the seal on the large locking ring that secures the fuel pump and sender unit to the tank.
Seen one on Youtube and it was one of the small fuel lines with a pin hole in it. I'll see if I can find it and post a link.

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[caluma4x4]

It's on a T4 but could be similar.
https://youtu.be/2z9qGE-ATBA
On another case it was the filler neck hose at the top, that was why it was only apparent with a full tank.


Sent from my ANE-LX1 using Tapatalk

[A4orce84]

Hello Everyone,

So a few weeks ago Mr. Matt Devo helped me replace the leak detection pump (LDP) on my car. UNFORTUNATELY, the gas smell still exists on a full tank and it still appears to be coming from the driver's side rear wheel well area. I will say though the smell had been reduced, but I still have a very faint gas smell in the garage and inside the car.

I've updated the troubleshooting list below with the most up to date information:

----
To assist in the troubleshooting, I have noted the following so far:
-Slight gas smell after I fill-up and have a full tank of gas.
-No CEL for gas light.
-Able to fill-up without issue (gas pump does not click-off or stop intermittently).
-Smell fades as it gets close to the 3/4 mark on the fuel gauge.
-N80 Valve replaced in September 2017.
-Fuel Filter replaced in April/May 2016.
-Fuel Pump Seals REPLACED (Drivers and Passenger side) in May 2018.
-Charcoal Canister REPLACED in July 2018.
-LDP REPLACED in August 2018.
----

When we replaced the LDP, I did not see any torn lines or anything. It also might be worth mentioning, that the last few fill-ups, if I did NOT fill all the way to a full tank (for example if I only put 5-7 gallons in the car) the gas smell does NOT exist. Only when I fill-up to a full tank does the issue rear it's head. At this point, I am at a loss on what the root-cause might be.

Are there other lines / hoses that are known to leak related to the fuel system that I should start checking more closely?

[Ol Dirty Noodle]

Maybe it’s the tank itself?

[A4orce84]

Tuesday Morning Bump, looking for some fresh opinions and ideas! TIA everyone for all your time and help so far!

[EuroxS4]

Check the passenger side seal on the tank make sure it didn’t roll and get cut when it got replaced.



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[A4orce84]

Check the passenger side seal on the tank make sure it didn’t roll and get cut when it got replaced.



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Both seals are installed properly and have no issues currently.

[imnuts]

When you replaced the seals, were the OEM or aftermarket? Any wet or damp looking spots you can see anywhere around the car?

Sent from my Pixel 2 XL

[A4orce84]

When you replaced the seals, were the OEM or aftermarket? Any wet or damp looking spots you can see anywhere around the car?

Sent from my Pixel 2 XL

OEM seals. No wet spots that I can see, just a very fumey gas smell in my garage the morning after filling up to a full tank.

[EuroxS4]

Ok I just remembered something else.check the seal on the gas cap check it for cracks.No faults set?


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[A4orce84]

Ok I just remembered something else.check the seal on the gas cap check it for cracks.No faults set?


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I would think if the seal on the gas cap was bad and had cracks, I would smell the strong fume smell from that area (I do not) and a CEL would be thrown (currently no CEL is going off). The gas smell is definitely coming from the driver's side rear wheel well area (where the LDP is located and was replaced).

Thanks for the good suggestions though, I appreciate it!

[Seerlah]

A suggestion, research if there is a dye that can be added to the fuel tank. That should maybe make diagnosing easier. For example, Motul has an oil that has dye already in it that can be traced with a UV light for oil leaks. Maybe there is something on the market that comes in the form of a fuel addative that works in the same manner?!?!

Gas dries very quickly. Maybe you are not experiencing vapor leakage, but actual fuel leakage that dries quickly and you smell the fumes (vapors). But the fuel dries before you can even spot it.

Edit: Quick Google search shows that it does exist and can be picked up at your local auto store (probably Walmart too).

https://shop.advanceautoparts.com/p/...rchTerm=Uv+dye

https://m.autozone.com/test-scan-and...our/835775_0_0

[EuroxS4]

Well the absolute best way to find a evap leak is smoke testing the evap system.Please note you have to clamp of the ldp pump filter when doing this.you would need a smoke tester for the evap system.Thats how the pros in the business do it.probably the most efficient way to do it.

[shurur9]

still want make my very own smoke machine..plenty DIYs on youtube.

[EuroxS4]

still want make my very own smoke machine..plenty DIYs on youtube.

Always an option whatever works


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[A4orce84]

Hello Everyone,

This fuel smell issue first appeared in the April 2018 time-frame has finally been RESOLVED. I wanted to give a final update and resolution below:

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Update:

So, I took my car to the local shop in town to perform a smoke test to see if they could identify where the leak (smell) was coming from. The shop identified that the driver's side fuel sending unit was the culprit and exhibiting the leak. I bought a used replacement from ebay, and upon pulling everything apart to replace the part, we were greeted with something that looked similar to the following:
https://www.audizine.com/forum/showt...1#post13391946

At this point, I was 99% sure the fuel sending unit was the root-cause that had been contributing to the smell for the past 6+ months. I am happy to report that after a few weeks (and a few fill-ups with a full tank of gas) the issue has NOT returned and I have not had any type of fuel smell!
----------------------------------------------------------------------------------------------------------------

HUGE thanks to Mr. Matt Devo for helping me diagnose the issue correctly and assisting with the repair! And to everyone else on the forums for helping with your suggestions / feedback / advice / etc. on what the issue might have been.

Hopefully, this helps anyone else who might have a similar smell / leak in the future! If anyone has any additional questions, please feel free to reply to this forum thread, and I'll reply when I can.


Thanks,
Asif

[MetalMan]

Thanks for following up. My old, also 2004 USP, had this EXACT issue. The connector area would fill up with gas, and wreak for a while. Could clearly smell it while the car was parked outside too. That was an expensive fix...
This is the picture I took of the crack:

[Timbert]

Here's where mine cracked, this is the passenger side, the pump housing itself, on my B7. Only leaked when the tank was at least 3/4 full and when it was down to 1/8 tank I cleaned and dried it and had to watch it closely as my son filled it at the station. The crack was mostly covered by the rubber boot to the electrical connector for the pump, but the red arrow shows where the fuel was seeping out.

IMG_3552 by Timberto Lopez, on Flickr

[Turbo510]

Had just this problem several months ago. My wife noticed the gas smell first, and it didn't take long to find the gas puddled in the driver's side tank cover, and the associated hairline crack. At first I expected to replace the cover, but it is expensive when new, due to including a tank sender, etc. But I did some checking on how well Epoxy resin resists gasoline, and have successfully solved the leak. So after the fuel level was below the plastic cover, I used my Dremel to scuff the plastic at the crack and a little around it. Then I used industrial-strength Isopropyl alcohol to flush the crack and roughened area. The Epoxy that I used is a slow-setting, high-strength type that we use at work, Cyberbond 5090. However, what you can get at the hardware store would probably be OK; I just wouldn't use the 5-minute stuff.

[shurur9]

My pump unit seal had rolled and fuel gushed out at fill up..

Fixed the gas smell by sprinkling fresh coffee grounds in the carpet and trunk area. Coffee supposedly soaks up gas smell. It may be a bit much for some folks, but worked for me.

You just vacuum it up after a time.

I did two treatments.

[EuroxS4]

I cant say I ever had this issue on my avant. Glad you got it sorted!!

[mrdoofer04]

When the engine is turned off the LDP (Leak Detection Pump) located in the drivers side rear wheel well opens up a vent to atmosphere to relieve any pressure build up in the gas tank. The expanding fumes in the gas tank get pushed out through the charcoal canister, scrubbed, and exit through the LDP vent. If the charcoal canister is defective the unscrubbed fumes exit from the LDP vent resulting in the smell of raw gasoline. This video is pretty long but it gives a really good explaination as to how the evaporative emission system works.

This is exactly what I was thinking about when he mentioned rear driver side wheel well


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[A4orce84]

Nothing like seeing one of your original posts get bumped back up to page-1. It's like being a proud father and seeing your son ride his bike for the first time...

Glad my post was helpful for you guys! =)

[mrdoofer04]

Nothing like seeing one of your original posts get bumped back up to page-1. It's like being a proud father and seeing your son ride his bike for the first time...

Glad my post was helpful for you guys! =)

I’m actually gearing up to start looking into my big turbo stroker B6. Getting fuel smell as well. I deleted the purge and it’s dumping to atmosphere under the car, but wondering if I have the same issues with my filter as well. I am also running a vented catch can so have thought it’s possible that I’m getting blowby vapors. I’ve considered adding a vacuum pump to the catch can system to see if that helps and also relieves some more crankcase pressure as well.


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