I’ve replaced all of the hoses on fuel system and installed new stainless steel fuel lines from motor to fuel tank, but still getting a fuel smell in cabin of my 1975 914. I took the gas tank out last year, and it was in good shape- no rust, etc. You can sometimes smell it when standing in front of car. It’s not overwhelming, but still smells like gas.

So, I’m thinking of doing a “smoke” test using dry ice and my homemade tester (see picture). I bought a spare gas cap and installed an air hosing fitting in it. I’m planning on hooking up to my air compressor at 1-2 pounds PSI and pushing dry ice smoke through fuel system. Has anyone done this? Any suggestions or advice would be greatly appreciated.
Thx, PDXBobClick to view attachment

https://www.amazon.com/AUTOOL-Automotive-De...3418acc7e5c967b


That's what you're trying to make?

Notice it's pressure output limit is .46 psi.

1-2 psi is "pounds per square inch"

How many square inches are there in the interior surface of the tank?

I respect pressure and vacuum. It's easy to burst or collapse things...

I've always used a smoke generator that burned mineral oil to do what you are trying.

The mineral oil smoke was visible for a long period of time. I'm not sure how long CO2 smoke stays visible in comparison.

This is a novel way to re-create a smoke generator.

I'm interested in if it will work.

Please post results.

What type of fuel hose did you use? Gas fumes could be permeating from the fuel lines. There is a newer type of fuel hose that is not effected by ethenol. Barricade fuel line by Gates.

is your vapor emission system still hooked up? or still intact?
ie the charcoal cannister (in the engine bay of a 75).
a small diameter plastic line runs to that.

Thanks Technicalninja.
Yes, I’ve used my homemade smoke machine in the past to find vacuum leaks and it’s worked well. I burned oil then, but with fuel system I thought dry ice would be safer. However, after checking out the Autool unit from Amazon that you linked, I think I’ll buy that one.

Yes, charcoal canister and all systems refurbished and hooked up. I’m thinking it must be something in front near gas tank (hoses, fuel pump,etc). Thanks, Bob.

Worse when the tank is filled beyond 3/4...?

Check for fuel under the carpet/board area at the front. Pull the cover under the master cylinder and see if there's any fuel residue there.

I had a vexing fuel odor for a while I could not nail down. Worse after a fillup, and worse after "spririted" driving. In the end, it turned out to be rust holes in the tank where the fabric/"carpet" bits were between the inner fender and the tank. Water retention in those bits rusted through the tank.

It started light at first but eventually grew to the point where I got a lot of fuel spilled on the garage floor after a fillup. Pulled the tank and there it was...

Click to view attachment

Did you replace the rubber gasket under the gas cap?

That where my 1975 fuel smell was from

Smells in the cockpit are usually pushed in from the front trunk

When you removed the gas tank, did you remove the all fabric felt buffer strips glued to the tank? That's where my tank had rusted out - from the outside of the tank through into the inside of the tank. Those fabric felt buffers trap water and moisture which causes rusting out after 50 years. I had the same symptoms of gas odors when the tank was full or during spirited driving. I too did the complete fuel hose and fuel gaskets replacements, all to no avail. Once I finally pulled the tank and removed the buffer pads, the source of the fuel smell was obvious as the area under the top most buffer pad was riddled with rust bubbles and pin holes.

Thanks. When I pulled tank I removed all felt material. But I wonder due to age if it has developed a leak like yours. Something to check.

Agree - check gasket under fuel tank cap. Check hoses at fuel pump, especially if old braided style as they may be saturated if there's even a small leak.

Most of the gas odor in my car is the result of Taco Bell