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1986 Mercedes 500 SEC
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Discussion Starter #1
Hello everyone!

I current own a 1986 Mercedes 500 SEC (Black exterior/Medium Red Interior)

I am getting a lot of fumes and a smell into the cabin, so I located the trunk's weatherstripping BUT I am having an extremely HARD TIME locating the firewall grommets and seals, ALSO how many are there and where can I find them??

Another issue I am facing is also locating the door's frame on the cars' body upper frame weatherstripping channels/seals!! They have stopped their reproduction BUT they are in NEED of replacing!

Please help on where to locate these parts and how many seals/grommets are there in the Firewall and Trunk! Thanks
 

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1991 500SEC 50K mi. 1987 560SEC Now 153K mi. 2020
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Does the car have odors in the cabin when you are driving at road speed OR is it mostly sitting at an idle, say at a traffic light?
Is it a raw fuel smell, or oil smell... or exhaust smell? Are the windows down when this occurs?

Do conditions change when the RECIRC is ON?

I ask these questions as it helps with the diagnostics... as to where the smell comes from, under what conditions..

Our 126 cars have cabin air extractors pulling air from the cabin through the trunk and out under the rear bumper cover, just behind each rear wheel well. They are supposed to act as a one-way valve > out as the car is moving & the windows & sunroof shut. Under those conditions, the interior of the car & trunk are at slightly higher air pressure than ambient. Open a window, even a little, the air pressure becomes negative, and one is more likely to smell exhaust from the rear of the car if there is a bad seal at the extractors, taillamps, fuel filler gaskets, drain or trunk seal.

If one is stopped at a light, te ACC can pull oil fumes / raw gasoline smell from a leaking EHA into the cabin through its air intake just below the windshield.

Good luck, man & Welcome to BenzWorld!

MBL
 

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1986 Mercedes 500 SEC
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4 Posts
Discussion Starter #3
Does the car have odors in the cabin when you are driving at road speed OR is it mostly sitting at an idle, say at a traffic light?
Is it a raw fuel smell, or oil smell... or exhaust smell? Are the windows down when this occurs?

Do conditions change when the RECIRC is ON?

I ask these questions as it helps with the diagnostics... as to where the smell comes from, under what conditions..

Our 126 cars have cabin air extractors pulling air from the cabin through the trunk and out under the rear bumper cover, just behind each rear wheel well. They are supposed to act as a one-way valve > out as the car is moving & the windows & sunroof shut. Under those conditions, the interior of the car & trunk are at slightly higher air pressure than ambient. Open a window, even a little, the air pressure becomes negative, and one is more likely to smell exhaust from the rear of the car if there is a bad seal at the extractors, tailamps, fuel filler gaskets, drain line or trunk seal.

If one is stopped at a light, the ACC can pull oil fumes / raw gasoline smell from a leaking EHA into the cabin through its air intake just below the windshield.

Good luck man & Welcome to BenzWorld!

MBL

Thank you for your reply.

Well, there is a smell both while driving and at idle; however, the smell is stronger at idle. I am assuming that the exhaust fumes are entering through the trunk since my trunk weatherstripping is torn at certain places and one of the tail lights is broken and will definitely let fumes in. The smell is more like an exhaust smell.

I am planning to replace all of the bad seals and weatherstripping in the trunk and rear.

Do you know where can I find the Firewall Seals and Grommets as well??
 

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84 500SEL AMG, 90 560SEC AMG, 85 500SEC AMG Widebody
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Most of the firewall grommets are no longer available. The main upper door seals (with the ribbed color coded cloth covering) that goes around the top frame of the car for the side windows are also NLA. Your only option is eBay for the parts you need. I doubt the fuel smell is coming from the firewall grommets. I doubt your firewall grommets are bad. If you are NOT getting water into the main cabin when you wash your car or when it rains, then I doubt your upper door seals are bad. Most likely the trunk seals. You may also have a fuel leak under the car that is adding to the problem. Check all of the fuel hoses around the fuel pumps and the fuel tank.
 

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1986 Mercedes 500 SEC
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Discussion Starter #5
Most of the firewall grommets are no longer available. The main upper door seals (with the ribbed color coded cloth covering) that goes around the top frame of the car for the side windows are also NLA. Your only option is eBay for the parts you need. I doubt the fuel smell is coming from the firewall grommets. I doubt your firewall grommets are bad. If you are NOT getting water into the main cabin when you wash your car or when it rains, then I doubt your upper door seals are bad. Most likely the trunk seals. You may also have a fuel leak under the car that is adding to the problem. Check all of the fuel hoses around the fuel pumps and the fuel tank.
Hey Alydon, Thanks for your reply.

Oh man, many critical parts are NLA. I agree, I think the smell is definitely not due to the firewall grommets, however there is a small leak that comes from under the steering wheel when the car is washed BUT NOT from the windows. The grommets are loose and not placed correctly and I just need to check the water channels to see if they are clogged or blocked.

Yes, I will also check the fuel lines, pump, and tank as well! I just got the car 4 months ago and I am slowly discovering and working on the car, plus this is my first Mercedes and C126.
 

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Premium Member
87 Euro500HVSEC. 88 Euro 560HVSEC. 89 Euro 560HVSEL
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4,266 Posts
You need to remove the windscreen wipers and then the plastic covers (in two pieces - left & right side that meet in the middle) to expose the drain box system along the complete bottom of the front windscreen.
There are drain openings in the middle and on both outer sides that have rubber hoses connected to drain water out under the firewall.
You need a small mirror to look along under the bottom of the windscreen as well top inspect for rust in the floor of the box channel
Often there is corrosion in the metal framework of the box channel which can be on the floor and/or walls of the metal channel.
This is also where the cabin flap is located on your right side that pulls in air from outside into the cabin
If there are rusted openings it can lead to engine bay fumes getting into that box chanell.

Also any of those firewall grommets to the engine bay ad where cables come through grommets they need to be sealing properly - if not use some black silastic (non acidic curing) or windscreen sealant to help the grommet make a good seal and especially where cables enter through the centre of a grommet.
Make sure your grommets in the trunk floor - under the spare wheel and in both sides of the those storage wells each side of the spare tire well are all sealing correctly.

And Yes - those venting flaps on the outer wall of each side storage wells need to be in good order and sealing when the car is not moving (they can be replaced as the whole plastic frame the rubber flaps swing from can be removed) - you need to remove your rear bumper to get good clear access to them from the outside
 

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1986 Mercedes 500 SEC
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Discussion Starter #7
You need to remove the windscreen wipers and then the plastic covers (in two pieces - left & right side that meet in the middle) to expose the drain box system along the complete bottom of the front windscreen.
There are drain openings in the middle and on both outer sides that have rubber hoses connected to drain water out under the firewall.
You need a small mirror to look along under the bottom of the windscreen as well top inspect for rust in the floor of the box channel
Often there is corrosion in the metal framework of the box channel which can be on the floor and/or walls of the metal channel.
This is also where the cabin flap is located on your right side that pulls in air from outside into the cabin
If there are rusted openings it can lead to engine bay fumes getting into that box chanell.

Also any of those firewall grommets to the engine bay ad where cables come through grommets they need to be sealing properly - if not use some black silastic (non acidic curing) or windscreen sealant to help the grommet make a good seal and especially where cables enter through the centre of a grommet.
Make sure your grommets in the trunk floor - under the spare wheel and in both sides of the those storage wells each side of the spare tire well are all sealing correctly.

And Yes - those venting flaps on the outer wall of each side storage wells need to be in good order and sealing when the car is not moving (they can be replaced as the whole plastic frame the rubber flaps swing from can be removed) - you need to remove your rear bumper to get good clear access to them from the outside
KRH Thank you!! This is great information.

My plan was to definitely remove the plastic covers and look under them to see what is going on. I will definitely look at the trunk and rear bumper area and also inspect and fix any issues!

I appreciate your detailed and informative post.
 
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