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Exhaust in the cabin...help, I'm getting dizzy...


Tdh
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So I get strong exhaust smell in the cabin, but only when the windows are down.  Whether its just the triangle windows cracked or fully open, one or both of the main windows open a little or fully, or any combination of either.  When all windows are closed, theres no smell, with the vents open or closed.  Weird.  

 

I replaced the exhaust from the down pipe back this past weekend, with no change.  Still smells like ass with the windows down, and nice and fresh with the windows up.  

 

Leaky exhaust manifold gasket maybe?  Any ideas appreciated.  

 

Thanks,

 

Travis

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exhaust often gets sucked in through the trunk and pulled into the cabin.

look at your trunk seal.

you can put a dollar bill on the seal and close the lid, then pull on the bill, to feel whether it is fitting tight.

a quick fix can be done sometimes, by bending the trunk's rim flange back up, where the seal is glued on.

(it is common to lean on that surface, while reaching into the trunk and it gets bent).

I noticed a little soot on the underside of the trunk lid, where it was leaking before I bent mine back.

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Paul,

 

It does extend out.  I bought the IE stainless system, and installed the tailpipe such that it extends well past the rear bumper.  

 

76, 

I'll check the seal.  It just seams weird that exhaust gets drawn in only with the windows open.  There's a speaker mounted in the tray, and its not sealed, so anything in the trunk would make its way into the cabin. 

 

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With the windows down and the car moving, the air speed outside of the car is higher than the air speed inside the cabin thus creating a lower pressure area in the cabin.  The lower pressure can then suck outside air/exhaust into the cabin.  I believe this is called the venturi effect.

 

Have you checked the seal between the shifter and the transmission tunnel?

Edited by Tsingtao_1903
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One way of testing the trunk is get some really strong air freshener trees like 3 or 4. Open them and put them in the trunk. Then drive around. Does the car smell like pina colada?  Then it’s coming from the trunk. Seal the area between the trunk and the car and Work tonseal the trunk itself. 

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Also check the seal around the gas tank and the fuel line holes.

Do you have a sunroof?  Non-sunroof cars have vents near the trunk hinges that can suck up exhaust fumes if: 1) the muffler connection to the center section is not air-tight  2) the exhaust tip is too short 3) the trunk seals are leaking  4) the pad is missing (or rotted) on the shifter tower 5) your peddle box is not sealed 6) your valve cover vent tube is not connected  tightly to the air cleaner

I'm sure there are a few more ideas....but this will get you started.  I know....this job is exhausting.

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No one has mentioned the vent air plenum hood seals at the base of the windshield. If there's enough blow-by in the engine compartment and those seals are leaky, it could smell like exhaust coming through the plenum. With the windows closed, less air is drawn into the cabin through the heater box. Just a thought.+

 

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FWIW - I've seen the "Uro" brand trunk seal installed, and it is slightly less tall than the OEM BMW seal. On one particular car, it did nothing to seal the trunk lid to the body. If you replace the seal, consider getting the genuine BMW part, instead.

 

If the rear parcel shelf is cut for rear speakers, this can be a source of incoming exhaust fumes to the cabin as well. 

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12 hours ago, JerryC said:

the vent air plenum hood seals at the base of the windshield.

There are actually three seals and three drains (AKA duck lips or elephant trunks) for the plenum chamber:  two side seals, through which the hood latching bar passes and a seal pressed into the trailing edge of the hood, that mates with the forward edge of the heater plenum chamber.  The two side seals are often deteriorated and will allow air from the engine compartment into the heater intake, which is also your fresh air intake.  New ones are available both through BMW and from Carl Nelson at LaJolla Independent.  

 

The three drain tubes at the base of the plenum chamber must seal properly at their nether ends; they're closed most of the time but will flex enough to allow water to drain.  If they're rotted, missing or full of crud so they're forced open all the time, that's a prime source of exhaust smell (which is probably hot/burning oil that you smell.)

 

Finally, as was pointed out previously, make sure the foam seal is in place underneath your shift boot.  That's another source of fumes, especially if you have a later car with the square shift boot.

 

mike

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