Leak at rear of car ?

[VroomTT]

**Update: Cause found - Cracked Fuel Level Sensor housing. Left side sensor in fuel tank access port on the driver side.**

So I parked my car outside to be able to adjust my garage door and I noticed a little wet patch toward where the back of my S4 would've been.

At first I thought, rear diff, but looking from behind it looked clean, then I poked around the driver side in front of the rear tire and see this...


I also sensed a strong fuel smell(which I had smelled earlier in my garage too), but that may have been from it just having run. I'm a little concerned about it being fuel bc of the strong smell, but I don't want to get ahead of myself...

Anyone know what this might be? Any input is appreciated as always

[Kambesama]

So I parked my car outside to be able to adjust my garage door and I noticed a little wet patch toward where the back of my S4 would've been.

At first I thought, rear diff, but looking from behind it looked clean, then I poked around the driver side in front of the rear tire and see this...


I also sensed a strong fuel smell(which I had smelled earlier in my garage too), but that may have been from it just having run. I'm a little concerned about it being fuel bc of the strong smell, but I don't want to get ahead of myself...

Anyone know what this might be? Any input is appreciated as always

Any previous work done? F.e: Fuel pump?

[VroomTT]

Any previous work done? F.e: Fuel pump?

No, it's the original fuel pump to the best of my knowledge. No work done to the car for a few months (other than the oil change and headlight bulbs which I did myself).

[Kambesama]

No, it's the original fuel pump to the best of my knowledge. No work done to the car for a few months (other than the oil change and headlight bulbs which I did myself).

The signs of it drying up and spreading the way looks like its fuel for sure. I would pull the rear seat cushion and open the covers for the fuel pumps and inspect. Also take note when it smells like fuel or begins to leak. If it happens when its full then something is probably wrong with the fuel pump o-ring.

[Lion Heart]

Maybe try putting a container under it and catching some of the drips (hard I know if it is fuel as it evaporates and so has to drip faster than it evaporates).

Then take it away from the car and smell it. You should know for sure then. Just an idea!

Maybe jack the rear up and get under there and try to spot the source of the leak. In the image it tends to be pointing towards a specific area, so hopefully won't be too hard to spot.

[VroomTT]

I double checked some of the records from the previous owner and the Fuel filter was replaced in Jan 2015 (which was right before I bought the car). "FS-tuning European Autowerks" up in Orlando did the work. That was with 80k miles on the car and it has 92k now. So maybe a botched fuel line near the filter? From the quick research I've done that seems to be common. Could this be caused by overfilling the tank??? I noticed lately since the S4 guzzles gas so much that I tend to try to really top it up... probly shouldn't do that and won't anymore, but could that be a cause?

Add to this, I went to go to work this morning and the battery was completely shot! She's sitting on a charger right now so I an hopefully get to any autozone or a local battery shop up the street to test the alternator and potentially put in a new battery. Also found the record for the battery which was bought in 2013 from AAA by the previous owner.

[VroomTT]

The signs of it drying up and spreading the way looks like its fuel for sure. I would pull the rear seat cushion and open the covers for the fuel pumps and inspect. Also take note when it smells like fuel or begins to leak. If it happens when its full then something is probably wrong with the fuel pump o-ring.

Great idea. Any insight into what I should be looking for? I'll try to dig up some fuel pump threads before going into it.

[VroomTT]

Maybe try putting a container under it and catching some of the drips (hard I know if it is fuel as it evaporates and so has to drip faster than it evaporates).

Then take it away from the car and smell it. You should know for sure then. Just an idea!

Maybe jack the rear up and get under there and try to spot the source of the leak. In the image it tends to be pointing towards a specific area, so hopefully won't be too hard to spot.

Yea, I was thining to back it up onto some ramps I have, but now the battery is dead... terrible timing on that one! The stain on the floor looked more like an oil or clear grease, but looking under the car it does look like fuel. Maybe fuel mixed with road dirt/oil?

I just the idea of leaking gasoline makes my stomach churn. Last thing I need is a hot FI exhaust getting gas on it

[Kambesama]

Personally AAA batteries are the worst ones i've ever seen. Sure they're free depending on your tow plan or insurance but they last only 1 - 2 years from my experience.
Fuel leak wise i'd say look for any lines that could have rubbed or are pinched. Most likely it isn't a fuel line because if it was i'd be leaking way worse. I'm leaning towards it being the fuel pump o-ring. Best way to tell is to do what I mentioned before. Fill tank full and see if it leaks. Also visually inspecting it is very easy too. Any kind of leak will create a clean spot around the area. For fuel especially since it cleans then evaporates. Look for those signs when you open up the rear seat.

[Kambesama]

Forgot to ask if any check engine light is or was on for EVAP codes?

[VroomTT]

Personally AAA batteries are the worst ones i've ever seen. Sure they're free depending on your tow plan or insurance but they last only 1 - 2 years from my experience.
Fuel leak wise i'd say look for any lines that could have rubbed or are pinched. Most likely it isn't a fuel line because if it was i'd be leaking way worse. I'm leaning towards it being the fuel pump o-ring. Best way to tell is to do what I mentioned before. Fill tank full and see if it leaks. Also visually inspecting it is very easy too. Any kind of leak will create a clean spot around the area. For fuel especially since it cleans then evaporates. Look for those signs when you open up the rear seat.

Yea, it was a completely shot battery and luckily the alternator is fine. I replaced it with an interstate battery I got a good deal on, damn those things are heavy!

Now that she's running I'm going to start looking into the fuel leak. I'll start by pulling off the rear seat and checking that out then report back.

[BCsniper]

Just give it a taste

[VroomTT]

Yup, popped off the seat and both covers. Passenger side was dry but super dusty, driver side was wet with fuel. There was a proper puddle of fuel inside there so that's def gotta be the source of the leak(and it's the same side). I cleaned it up a bit and the line/connector seemed okay. It was admittedly difficult to see though, and it was so bloody hot in my garage I had to stop for a minute.

Uploading pics now and will post up in a sec.

[VroomTT]

It's hard to see in this pic, but there if fuel pooled towards the right side where the electrical connector is. The hose and nipple connection seemed fine at first glance.



I'll need to get a shot of it cleaned off too.

Open to advice. Thanks guys!

[Lucca M]

if you have second person to see whats going on, have that person watch the fuel pump when you crank the car. im 90% sure they installed the rubber gasket surrounding the fuel pump assembly wrong or ripped it. those fittings are usually pretty strong, so my bet is on incorrectly seated pump. pop the ring out and see if the gasket is sitting ok or not, and just replace it if needed.

[Kambesama]

Yup, popped off the seat and both covers. Passenger side was dry but super dusty, driver side was wet with fuel. There was a proper puddle of fuel inside there so that's def gotta be the source of the leak(and it's the same side). I cleaned it up a bit and the line/connector seemed okay. It was admittedly difficult to see though, and it was so bloody hot in my garage I had to stop for a minute.

Uploading pics now and will post up in a sec.

Nice find! Hopefully you can trace it to its exact location. Another thing i've seen but its not with our cars tho. Some BMW can burn the fuel pump connector and literally melt the area around it causing a hole. Just to be on the safe side, remove that connector to inspect once you clean it up a bit.

[Kambesama]

I could be wrong and if someone else can correct me. The driver side fuel pump is only the jet pump and the passenger side is the main feed pump correct?

[VroomTT]

Cleaned it up a bit last night and grabbed a shot this morning... Doesn't look cracked. Might be the nipple fitting or maybe the gasket as suggested above.


I really need a second person to turn on the car while I watch in the back. I'm going to try to swing by my local audi guy's shop omw home today to see if he can help diagnose.

[VroomTT]

I should also note that i just filled up too, and what I'm reading says it's best to wait till the tank is almost empty to open up the pump. Thoughts?

- - - Updated - - -

if you have second person to see whats going on, have that person watch the fuel pump when you crank the car. im 90% sure they installed the rubber gasket surrounding the fuel pump assembly wrong or ripped it. those fittings are usually pretty strong, so my bet is on incorrectly seated pump. pop the ring out and see if the gasket is sitting ok or not, and just replace it if needed.

Thanks for the tip! Any chance you could point me to a link of that gasket so I know what to look for?

[Lucca M]

When you pull the white "lid" of the pump assembly off then you should see a gasket surrounding it, sometimes it comes out with the lid sometimes it stays on the chasy. It basically seals the fuel pump so im sure youll find it.

[Lucca M]

https://www.ecstuning.com/b-mtc-part...j0919133b~mtc/

[VroomTT]

When you pull the white "lid" of the pump assembly off then you should see a gasket surrounding it, sometimes it comes out with the lid sometimes it stays on the chasy. It basically seals the fuel pump so im sure youll find it.

Awesome, thank you!

[VroomTT]

I could be wrong and if someone else can correct me. The driver side fuel pump is only the jet pump and the passenger side is the main feed pump correct?

I think you are correct. From what I've been reading the actual fuel pump is on the passenger side, and the driver side has a "sending unit". I'm not entirely sure the purpose of it, but I'm hoping it has the same type of gasket/seal on it as the one mentioned above.

[VroomTT]

Oh man, so good news, bad news, and maybe news... lol

Good news: I sourced the fuel pump seal from the local vw dealership for $12. Popped by omw from work and grabbed it.
Bad news: Got home, pulled the cover off and started cleaning it up properly. Upon closer look, I found out it's actually a small hairline crack in the cover which is the cause of the leak. It's the tiniest little crack too

Here you can see it in the corner just above the electrical connectorr. It's about 1cm long total ans just seeps gas


Maybe: So I know i'll need to replace the sender unit, but since I'll need to order it and I want to be able to get around this weekend, I'm considering gluing it! (I know, ridiculous in an S4! lol)
My main question is, would it work? I'm already looking into options and plastic epoxy is probly the way to go. I almost put a couple drops of Gorilla glue on there but my better judgement prevailed. I should be able to just drip a bit down that edge to seal up the crack short-term(or i guess longer if it hold problem free, but im planning to replace it)

Anyone have experience with something similar? Suggestions on a better glue?

[Lucca M]

Id try to epoxy it or find a donor pump from local junk yard (a4 is the same unit different motor) and transfer everything from yours to the new/used one?

[VroomTT]

I stopped by Ace last night and picked up some plastic epoxy, but also saw this stuff.

Looked like it was exactly what I needed so I decided to give it a shot.

Should be fully cured by 9:30am est today...

[VroomTT]

Well, that tank repair stuff was a total bust! It think I actually got a bad batch of the stuff because it never even cured. I knew it seemed off while mixing bc it was crumbling, but I had never used this stuff so I tried anyway. Def should've trusted my gut. Oh well, it all came right off since it never cured. So no harm but just a waste of time.

Tried again with the 2 part plastic epoxy I got (so glad I bought both just in case!). Stuff seemed strong and was a little easier to work into the area. 24hr cure time, so we wait again...

[VroomTT]

Also, just for the relevance of this thread in the future, this is the part that im fixing/replacing.

Fuel Level Sensor - Left



https://www.ecstuning.com/Audi-B7_S4...Unit/ES436468/

[Kambesama]

Well, that tank repair stuff was a total bust! It think I actually got a bad batch of the stuff because it never even cured. I knew it seemed off while mixing bc it was crumbling, but I had never used this stuff so I tried anyway. Def should've trusted my gut. Oh well, it all came right off since it never cured. So no harm but just a waste of time.

Tried again with the 2 part plastic epoxy I got (so glad I bought both just in case!). Stuff seemed strong and was a little easier to work into the area. 24hr cure time, so we wait again...

Dang.... GL with repairs OP. Glad you were able to pin point the location. If anything also try sealing the tank from the inside out for that added protection.

[VroomTT]

Dang.... GL with repairs OP. Glad you were able to pin point the location. If anything also try sealing the tank from the inside out for that added protection.

Thanks Sealing from the inside out is not a bad idea at all. Though, I guess if I was going to go through the trouble of pulling it out, it really would be better to just replace it.

I'm holding out for some luck with the epoxy! (fingers crossed)

[VroomTT]

Epoxy cured up nicely and while it doesn't look great, it's doing the job



Plastic epoxy seems like the right stuff to use here. Once cured it's effectively become the same plastic material, almost weld like. Good stuff to have for future broken plastic bits

[Lucca M]

Im glad you were able to fix it!

[VroomTT]

Im glad you were able to fix it!

Thanks! I'll probly pop the seat off again later this week to see how it's holding up, but fingers crossed for now...