Gas and Exhaust Odors in the Cabin

HB Chris

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It is not uncommon for driver or passenger to complain about gas and exhaust odors when driving in your coupe or sedan. Here are some tips to hopefully alleviate this issue:

The front of the coupe needs good rubber seals around the fresh air plenum, both of these are in front of the windshield. Also critical are the two rubber drain snorkels and the rubber blanking plugs in front of the hood latch mechanisms. This area needs to airtight from the engine bay.

The trunk needs a good rubber seal as well as a good o-ring seal on the fuel level sending unit. Also, the pipe on the sender uses a plastic sleeve so that the 8mm fuel hose is tight to the pipe. The one that many ignore is the gas tank venting system. On US coupes the gas tank filler pipe has a hose that goes to the fuel vapor catchment tank on the right side wheel arch. From there a blue plastic line runs on the right side of the car and emerges in the engine bay in front of the passenger. From there it goes to the charcoal canister under the battery and then to the bottom of the air cleaner. There are four places where 6mm fuel hose is used between the plastic pipes and the hard points. Vacuum from the air cleaner draws fuel vapors contained in the trunk’s tank through the filter and into the engine. Even when a coupe is converted to FI it is good to have this system remain intact. The trunk seal prevents exhaust gases from being sucked into the trunk and into the passenger compartment while driving. Other areas that should be checked include:

Speaker holes in the rear parcel shelf. If those are not sealed properly by the speaker or if the speakers are damaged or removed that creates a direct opening into the trunk. There are several holes in the firewall through which wires or connecting rods pass through. Over time these disintegrate and create opportunities for fumes to pass through:
- The grommets through which wires pass through the firewall on the drivers side are often perished.
- The pedal box has a few areas with rods passing through potentially deteriorated grommets
- On fuel injected cars the DME wires pass-through on the right side. Another leak opportunity
 
Good write-up. I will add some pictures in a next post to support your explanations. It may help people to recognize the parts.
I experienced myself the same fuel smell dilemma, it was the reason my wife hated the car before it was fixed (new fuel lever sender O-ring).

(For the following, add or delete as you desire:))

I'm not really sure if the speaker holes in the parcel shelf make any difference though; there are about 30 holes other between the trunk and the interior cabin.
Summary of my story: If you have vapors in the trunk, I think it is not realistically possible to keep fuel vapors from passing from trunk to interior: the vapors need to be prevent from being created outside of the combustion chamber.

Openings between trunk and interior are plentlyfull:
The one most noticeable is between the quarter panel and the wheel well. It's open from the trunk directly to the front, behind the door panels. In the pic below you see the QP on the right; at the top is a separation panel with a rubber, but below that rubber is a gap to the wheel well edge / fender lip.
Also the wheel well has this reinforcement ridge on top; on the left of tis ridge teh trunk lid hinge bracket is welded. Between those two parts are also 2 holes to the interior cabin: You can even see a spot of light in the below pic, which is an opening to the cabin. On the left side of the car it also passes the cable harness.

20201211_220907.jpg

The other large openings are on the trailing edge of the parcel shelf, they open on the other side to the trunk.
1655111981639.png

the other openings are mostly small round openings on the parcel shelf. Some of them are for the snap clips of the parcel shelf, but some larger ones have no purpose. those could be closed easily, but at least they aren't closed from factory:
20200526_231309.jpg
 
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pic with parts as referenced by HB Chris:

Fuel level sender has a 6 mm round tube, but the ID of the rubber fuel hose is 8mm. from factory our cars came with a white plastic sleeve: 6*8*20 mm. these often crack, or are thrown away (by accident) when replacing old fuel lines.
part is for sale as a standard bushing in PolyAmide, which should be fuel resistant, at least in Europe through Fabory (Grainger in the US?): 56772.080.006

20170214_222902.jpg


this fuel level sender also has its own O-ring: Here a picture of a cracked one:
1655117512288.png

O ring has partnumber 16111744369, dimensions: 58.8x4.2mm

2 holes in the upper section of the firewall that needs rubber flat plug (see mouse pointer in pic):
1655115762352.png
1655115945049.png
1655117264000.png


drain hoses: 2 of these should be located on the upper part of the firewall. there two 4cm wide tubes exit into the engine comp:
Here:
1655116504814.png
1655116253634.png

available here: https://www.wallothnesch.com/en/hea...-2-5-cs-3-0-csl-e9/catalog-picture-64-03.html
 
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the pipe on the sender uses a plastic sleeve so that the 8mm fuel hose is tight to the pipe.
If anyone needs this sleeve, PM me with your address and I'll send you one for free. This is one thing we check first on the 2002s we work on because they are almost always cracked or missing entirely. Here's the instruction sheet on installing the sleeve.
 

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