User 52121

Anybody else ever run into this?

Trying to figure out where the stink is coming from... but the last few times I drove the car, it got pretty bad. As I'm anticipating getting the car back in a few days from a motor transplant, I'm starting to think through all the issues I hadn't yet sorted out last summer.

The car is mostly a track rat.... has carpet, door panels, dash... but not much else. No headliner, pillar trim, or any of the trim/carpet in the rear hatch area. Also the OE hatch has been swapped for a fiberglass unit (with integrated wing mount).

If I drive around town with the windows down... pretty quickly I can smell exhaust in the car. On a long enough drive, I have to roll the windows up and run the climate control... otherwise, well, it's too much.

I can cruise around all day long with the windows UP and not have ANY problems. As soon as I roll them down... the interior starts to fill with fumes.

Initially I figured it was the rear hatch seal, so I tried adjusting it a bit (essentially lifted/raised it to where I was sure it was pressing snugly against the hatch) but that didn't seem to do anything. I checked the seal for the engine cover (thinking perhaps air was coming in that way) but the seal was in good shape there.

My next step is to start looking for a complete rear hatch interior set (carpet/panels/etc) to see if that'll seal it up, as well as looking for a stock complete hatch to swap back on and see if the fiberglass hatch is the culprit.

Anybody else run into this?

Macster

There was a recent thread in the Boxster forum about smelling "exhaust" in the cabin of a Boxster. The final answer was apparently the car suffered some kind of electrical fire (?) possibly from an incorrectly routed or loose electrical wire/cable.

You will have to remove the engine cover and expose the engine so you can make a thorough inspection of the engine compartment and under the intake.

While I don't get the odor in the cabin with the windows up or down occasionally, less than occasionally, I'll get an odor that is less exhaust and more like something burning. I think what happens is something blows up under the car and contacts the hot exhaust manifold and sticks and then chars and this is the odor. Once I found a small piece of charred plastic wrap on the engine down under/around the intake runners.

The cabin is kept sealed against exhaust gases from the rear by some kind of air vent/air flap system located in the back of the car. Attached is a pic of the rear of my Boxster with the bumper cover and spoiler removed. There is a flap inside the flattened rubber "tube" on the side of the sheet metal under the tail light. While you can't see the entire vent you can just make out a corner of it in the flattened rubber tube.

The flap mechanism is rubber (?). The flaps are closed from gravity but when the car is moving and the area behind the car is in a lower pressure zone cabin pressure is greater and the flaps open from the pressure difference and allow cabin air to flow out and exit from these now open flaps.

If those vents were removed as part of the work to convert the car into a track rat with the windows down the cabin could be subjected to low pressure and air from behind the car could be pulled into the cabin.

User 52121

Hmmm ok thanks for the tip. I've seen that valve and assembly before, I just can't remember where (my car or another of several I've helped work on over the years).

If that valve's purpose is to keep exhaust from backing up in the cabin... then that sounds like the likely first place I should check. Thanks!

badabing

Since your car is a track rat what mods have you done.

No cats? That will kick up a stink in some cars. Modified fuel map?

Also, suggest doing a thorough inspection of exhaust system for leaks. Even smoke test if necessary.

User 52121

Well the car used to have some kind of race header (it was a parts bin find from the shop), B&B catback, no cats. (It was also a 4.0L build). I eventually had a Mase Engineering custom tune done *BUT* the fumes were a problem before the tune.

Current build is a 9A1 swap, stock 3.4, stock exhaust. Haven't driven it yet, still waiting on the shop... but I'm expecting the problem to still be there. Just trying to get my ducks in a row for what to look for once I actually get the car back.

goatpaste

Did you get to the bottom of the exhaust smell? Was it the rubber flaps letting in gases through the trunk? I have 987 Boxster with the same problem and I just had a look at the flaps and the left one is sitting slightly open, I guess a couple of mm. Perhaps that’s letting exhaust gas in via the trunk...

Frank V

I have this problem as well. In my 2013 Boxster S when I have the top up everything is fine. When I put the top down i can smell an exhaust/burning smell. The burning smell seems to go away if I turn of the Hvac system completely.

I have a code for an engine compartment exhaust fan so perhaps that is the issue? Maybe fumes are coming out of the side vent with the broken fan and filling the cabin? I’ll have to replace the fan and see.

allen986

Not on my Porsche but I recently had this problem on my 2004 Nissan truck. It turned out to be an engine oil leak that I was putting off getting repaired since it wasn't serious. The smell got to be worse than the leak so I had it repaired. No more odors. The engine would heat up the oil on the surface and it would smell like exhaust.

Frank V

Just following up. I replaced the drivers side engine compartment fan and the smell is gone. My 2014 BS was throwing a code for this issue so if you have a smell you may want to check for codes. I also noticed that the driver side side vent was warm while the passenger was cool...one way to check which fan is broken.

Fix was easy from below as the fan pops out with moderate force. The trick is to flip it 180 degrees so you can snake it out between all the suspension components.