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1969 Mustang Coupe
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Discussion Starter · #1 ·
On my 69 Coupe there is and always has been a fume / smell that gets hard to take after a while. Used to think it was a symptom of the poorly installed exhaust when I bought the car but that has all changed now and the fumes have not. I've done a pile of work to the car since buying it, the entire interior is re-done, entire inside is sealed, X-Matt from one end to the other, new windows, new seals everywhere (for whatever they're worth on a 69 Mustang), and a complete new exhaust system.
The engine is (history unknown) 302 with long tube headers, Edelbrock carb, Edelbrock Performer, MSD ignition and a few other goodies. Car doesn't burn oil (that I can see) and runs very well. There is a possibility the car is running a bit rich, I have bought an Edelbrock carb tuning kit but have yet to tear into the carb to see what I can do. I have a PVC Valve (seems to be flowing free) on the passenger side of the motor plumbed into the base of the carb and a K&N breather on the other side. I do notice a fair amount of smoke? coming from the K&N breather at times and am wondering if that is what is making its way into the inside of the car. I have thought about making a suction tube to cup against one side of the breather and have the other end attach up under the air filter into one of the knockouts in the air filter bottom plate. Not sure if that will help but I seem to remember older vehicles of mine having something to that effect. One of my older Chevy trucks had a hose going to the old steel air cleaner into a small filter and coming from the top of one of the valve covers.
So to you engine Guru's, do you think these "fumes" are a result of a motor running slightly rich or due to oil fumes from the breather and what should I do to fix this?
 

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How far stick the tips of the exhaust pipes out? If they are too short exhaust gas can get sucked into the trunk and find there way into the cabin. This usually gets worse with the windows slightly open.

Did you check for leaks in the trunk area? A flashlight in the trunk at night helps finding leaks.


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If you have smoke coming from the K&N breather, then your PCV is too small, or you have some ring sealing issues. Air should be flowing into the breather, not coming out. You could try a closed factory style air cleaner with a breather hose to see if that helps.
 
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Mustangs are known for low-pressure areas sucking fumes in from the exhaust system, especially around the deck lid seal and any unplugged holes in the rear such as bumper brackets, wiring grommets, etc. I'd check the trunk seal first. Take some butcher or kraft paper on a roll and cut 1" strips across the paper about 1 inch wide all the way across except the last inch. Place the strips across the trunk seal area then shut the lid. Working around, tear the last bit of uncut paper then try and pull the newly "loosened" strip out. If it comes out relatively easily, you have a sealing issue. A well sealing trunk won't let you pull the pieces without a LOT of effort. When one comes out, mark the area with a piece of masking tape so when you're done you can open the lid and inspect the area(s).
 

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How far stick the tips of the exhaust pipes out?
Extending the tail pipe outlets a few inches past the rear valance cured my stench.
 

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I fought a terrible stench problem on my 67 for several years. I rebuilt the 2V carb, no help. I put a 4V intake and carb on that I rebuilt (and ran on the car years ago). Still stunk. I finally bought a new Summit 4V carb and it solved my problem.
 
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You can also place painters blue tape over most of the trunk, window, door seams and take it out and see whether the issue went away.
However, based on the smoky breather, I do suspect some blowby- which does stink, and will get in the cabin through various access holes in the firewall no matter what. Try to address the PCV as stated, and consider a leak down or compression test.
 

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Gas vapors can come from the rubber fuel filler tube hose too. Many that I replaced look good on the outside, but were severly cracked on the inside with fuel vapors coming through.
 
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Discussion Starter · #11 ·
Thanks for all the great tips, I will work through each one and see what I can find. Certainly not impossible for fumes to work their way into the car via the firewall as there could be holes I haven't discovered. Not likely on the floor as it was completely done over, sprayed and X-Mat covered, new seals everywhere and new interior. I sprayed the entire trunk area after stripping it, with with undercoat/truck liner and got into every nook and cranny. Not impossible but unlikely its getting in there. My tailpipe tips extend nicely beyond the back of the car and at one point stuck out way too far IMO. The trunk lid has a new seal on fresh paint and a well fit lid, I will though do the paper trick just in case there is leak, wouldn't surprise me if there was a spot.
I will check out the vaccum valve side of the engine and make sure it is working as well as I thought it was, very possible that it is not. Never made sense to me that smoke could/would come out of the breather if the vaccum side was working as it should.
 

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A lot of people don't put the strip caulk under the gas tank flange when they replace the tank. That's another place where fumes can sneak in.
 

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I went through every hole in the firewall and used plugs and sealer the close them up. There were a lot of little ones so look closely. I also had issues when the vent window was just open and not the fresh air vent, too.
 

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Discussion Starter · #16 ·
Windows down or up?
Mostly down but after a while with them up you can still sence the smell. It makes my eyes sore and definitely not pleasant for the old lungs.
 

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If you wanna clear the smells...drive faster...that is also what the triangular window things are for, bringing in fresh air to push the gasoline/methane/C02/oil smells out.

/s
 

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Is it exhaust or crankcase fumes you're smelling?
I agree you need to identify what you are smelling before you can track down where it is getting in.

Take off the oil filler cap with the engine hot and stick your nose near it to know what hot oil smells like. Same with exhaust pipe.

I had exhaust smell for years in my 65 and it ended up being because of the straight out tailpipes. Downturned tailpipes fixed it.
 

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It might be worth checking the connections on your exhaust and bolts. Check the headers all the way to the back of the car to make sure everything is tight and connected well. Just a tought.
 
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