[E9xjake]

Hey guys. I have 2009 e90 335xi. Has been single turbo for 4 years now. Over the last year or 2 I have developed a terrible exhaust fume smell coming into the interior. It pretty much happens any time it makes boost once the car is warmed up. I just had an exhaust leak fixed hoping that would fix it and it did not. The v band behind my turbo is tight.

Car has bmw cowl filters and is obviously cat less, but the smell is excessive and makes it hard to drive with the windows up.

Any suggestions or anyone with a similar issue? The smell is very strong and smells like exhaust. Definitely makes the car harder to enjoy.

[Serf27]

What exhaust?
Do you have the small foam rings around the fuel pump access covers?

[E9xjake]

Originally Posted by Serf27

What exhaust?
Do you have the small foam rings around the fuel pump access covers?

Exhaust is basically stock but custom, has the downpipe from doc race and then secondary cats are gutted, stock res is still there and then no mufflers.

And I'm not sure about the foam rings. You mean for the low pressure pump under the seat? I did actually try to see if the smell was somehow just fuel but I really feel like it's straight exhaust fumes

[HondaRC51]

Possible the exhaust seal ring on the downpipe is shot and needs to be replaced?

I think what Serf is saying is if that rubber seal is not there, than there is a chance exhaust fumes are leaking up from under the car and coming in through the opening where your fuel pump access is and thus coming into the cabin that way. Friend of mine did a custom turbo setup on his Ford Focus and cut a hole in the back to swap the pump easier. Never sealed the hole and it always smelled like exhaust inside after that.

[E9xjake]

Originally Posted by HondaRC51

Possible the exhaust seal ring on the downpipe is shot and needs to be replaced?

I think what Serf is saying is if that rubber seal is not there, than there is a chance exhaust fumes are leaking up from under the car and coming in through the opening where your fuel pump access is and thus coming into the cabin that way. Friend of mine did a custom turbo setup on his Ford Focus and cut a hole in the back to swap the pump easier. Never sealed the hole and it always smelled like exhaust inside after that.

Originally Posted by HondaRC51

Possible the exhaust seal ring on the downpipe is shot and needs to be replaced?

I think what Serf is saying is if that rubber seal is not there, than there is a chance exhaust fumes are leaking up from under the car and coming in through the opening where your fuel pump access is and thus coming into the cabin that way. Friend of mine did a custom turbo setup on his Ford Focus and cut a hole in the back to swap the pump easier. Never sealed the hole and it always smelled like exhaust inside after that.

Is this the ring you guys are talking about? Or is there something I'm missing?

I will say my air conditioning and heat does not stink, so it probably isn't coming through the vents like I originally thought, so maybe we are on to something

[Serf27]

Yes that foam ring.

How did you find your first exhaust leak?

The Dow pipe seal may also not fully seat if the downpipe has been removed a few times.
Can you drop the exhaust and look for any pinholes, usually with a trail of black dust.
The rear vent release flap behind the rear bumper could also let exhaust smell in if there’s another leak.

[E9xjake]

Originally Posted by Serf27

Yes that foam ring.

How did you find your first exhaust leak?

The Dow pipe seal may also not fully seat if the downpipe has been removed a few times.
Can you drop the exhaust and look for any pinholes, usually with a trail of black dust.
The rear vent release flap behind the rear bumper could also let exhaust smell in if there's another leak.

I found my first exhaust leak because I had a exhaust clamp on from having my secondary cats gutted. The clamp kept coming loose. Had it welded a week ago.

The downpipe has never been removed from the turbo. I checked the v band on it and it looks fine, and when idling it doesn't seem like anything is leaking under the hood or anything.

As far as the rear vent release flap, what exactly are you referring to? Please elaborate

[Serf27]

This piece. Top right on the body.
Any difference in smell if you push the recirculate button with heat/ac?

[E9xjake]

Originally Posted by Serf27

This piece. Top right on the body.
Any difference in smell if you push the recirculate button with heat/ac?

No difference there with the ac. However those vents I have airlines ran through I'm pretty sure, because my car is bagged.

I just want to add that my buddy has a catless n55 f32 and riding in his car vs mine is a night and day difference when it comes to smell. His doesn't smell. Mine, I can't ride in without smelling like exhaust the rest of the day.

Also I have checked the foam ring for the low pressure pump access cover and that is in tact, and I have also tightened my v band clamp as much as I can on my turbo.

[Serf27]

If the flaps are open, that might be where the smell is going into the cabin, from the exhaust tips or an exhaust leak.

Any weld point could have a leak too.
You have welds for the muffler delete, and both secondary cats.

The doc race kit has the downpipe mounted to the turbo, a second downpipe connecting to the first one and the second pipe also splits into the 2 stock exhaust pipes?

I’d look at the gaskets between the exhaust and downpipe too.

[E9xjake]

Originally Posted by Serf27

If the flaps are open, that might be where the smell is going into the cabin, from the exhaust tips or an exhaust leak.

Any weld point could have a leak too.
You have welds for the muffler delete, and both secondary cats.

The doc race kit has the downpipe mounted to the turbo, a second downpipe connecting to the first one and the second pipe also splits into the 2 stock exhaust pipes?

I’d look at the gaskets between the exhaust and downpipe too.

Originally Posted by Serf27

If the flaps are open, that might be where the smell is going into the cabin, from the exhaust tips or an exhaust leak.

Any weld point could have a leak too.
You have welds for the muffler delete, and both secondary cats.

The doc race kit has the downpipe mounted to the turbo, a second downpipe connecting to the first one and the second pipe also splits into the 2 stock exhaust pipes?

I'd look at the gaskets between the exhaust and downpipe too.

I'll have to check the welds. The gaskets on the y pipe to factory exhaust have actually been done before, so I don't think that is it but I will check that too. Other than that, maybe where the main downpipe meets the y pipe. I'll have to check it out.

I'm starting to wonder if this is just the reality of the car. No cats with open dumps. The strongest smell is when I actually do a pull and the wastegates open. So regardless of exhaust leak I'm probably gonna get the fumes from that. I'm okay with some smell because obviously being catless, there will be smell. But this just doesn't seem normal to me. If it is, oh well, I'll deal with it.

I definitely get smell though even just using cruise control on the highway. If the car has to go uphill a bit and use the throttle, it will be enough to smell. That being said, there is no smell coming in on a cold start. It really is only under load. That's what throws me off. If it was an exhaust leak, why would it not smell on cold start inside. It's just weird that it needs a load on it to stink the interior up. It has to make boost in order for it to happen it seems.

[Serf27]

What gasket did you use for the Y pipe?
The oem ones turn into a crisp and no longer seal.
I think I have a Hyundai or Kia gasket there.

Maybe the smell/leak isn’t strong enough to notice at idle/cold start or the leak is tiny and needs a lot of airflow to make its way out?

I’d say it’s not normal.