3.6 Conversion Fuel Smell, EVAP System Rebuild??

[Duc Hunter]

My 1975 Rat Rod is having a strange problem. As I am driving down the road, if I roll down the window the smell of gas is overwhelming. Roll the window up and it goes away pretty quickly. Parked in my garage and running the fuel pump to circulate fuel there is no fuel smell, even after pulling the shifter and tunnel covers to see if there was fuel leaking in there etc. There is absolutely no fuel leak that I can find. Even running the pump for 10 min there is no smell anywhere (Frunk, tunnel, engine bay), no fuel drips, etc.

The car is a 1975 with a 964 motor. It has the white fuel expansion tank and its vent line runs out to a charcoal canister (non-Porsche). I connect the vent line of the canister to atmosphere by running the hose out to behind the front bumper. There is no line back to the engine for vacuum, etc. I also have the expansion tank mounted backwards from stock. Meaning the end with 2 hose connections is up, with the one that goes to the charcoal canister up high so as not to let fuel get into the canister. The way they are mounted in my Carrera is with the end with both hoses it down (towards the tank) and any fuel in the expansion tank can flow down that hose to the canister (weird). I believe I added the charcoal canister to reduce the smell of fuel in my garage, but to be honest it's so long ago I forget why I did it. I took to charcoal canister off in my shop and there is no fuel smell in the frunk with that line just open. If I blow into that line to pressurize the tank, obviously there is a significant fuel smell that comes back out.

Any thoughts on finding my fuel smell, and eliminating it? Short of searching around for it with a lit match? If I don't want to add the purge valve, solenoids, etc to make a properly working EVAP system, cant I just vent the expansion tank into the filler neck (removing the canister from the loop) and be done with it?

[Duc Hunter]

Wow everyone’s as stumped as i am that does t happen often

[EC900]

A while back i removed my expansion tank along with the washer tank to do some repairs. Not having the exp. tank lines attached and dangling surely increased the gas fumes entering the cabin.

Is there any chance you reversed your hoses during the mod?
Old char canister can be blocked up but since you’re not actually using it as intended why bother with one, w/o vacuum there’s nothing pulling fumes into the combustion chamber anyway.
If venting out to air, best if hose was far enough behind the draft so not to enter cab.
Check the overflow hose on filler neck is intact or swapped with evap hose.
Also, check the condition of your filler cap gasket, mine was quite compressed.

[PeteKz]

I'll lay a bet that the expansion tank under the dash, just ahead of the fuel gauge, has a split in it. I had the same symptoms a couple years ago, couldn't find the source, but finally sat down with the fuel system diagram and traced it in the car. Stick your nose as close to that tank as you can and see if that's where the fuel smell is strongest.

[kd126500]

i have a similar set up. I just run the vent line out the front fender and do not notice any excess gas smell. How long is your vent line? When I originally set mine up I did notice it was too long and some of the vented fuel pooled in the line.

[BoxsterGT]

Fuel Hose "Permeation" is a possibility.

What hoses are being used? Are they AN Hose of an unknown origin, possibly from China?

Just asking, as this has happened before.

Len

[Duc Hunter]

Just an update on this. My 1975 was not running when I bought it. So there is nothing under or by the dash. My car only has a vent line out of the fuel tank, into the vapor canister (3.2 style) that catches the fuel vapors and lets them recondense and drop back into the tank. Out of that a line goes to the filler neck, another goes out to the charcoal canister (mounted next to the battery). That has a purge nipple I am not suing, and the vent line just goes out to behind the fron bumper. I may run that vent line back to the intake between the air filter and the throttle body. I am a little leary of this though, as if fuel vapor builds up in the intake it can ignite when you're cranking and blow the intake off. Common problem on Panamera and Cayneeene V8’s, among other cars.

[Duc Hunter]

Just following up. I have found several screwy things with my vacuum lines in general. Some are clearly related to the evap system. Does anyone have an actual vacuum diagram for the 964 engine? I cannot find one anywhere (I can find them for a 951 all day long, go figure).

In leu of a diagram I have pieced a few things together from other threads (pics below). It looks like the vacuum part of the EVAP system is just looped around on itself on my engine, but I cannot be sure based on the pics below.







Based on the pictures above, the middle one esp, on my car I see the lines I need for the charcoal canister. In my car the line to the charcoal canister after the check valve is simply looped back to the intake manifold. The other end of that says it goes to a venting valve in the pic....but where does the other end of that line go to? I am thinking I could unload these lines, and connect end thats labels to the charcoal canister to my charcoal canister...but then I would have a rather large vacuum port on the intake to plug, which seems wrong.

I assume there's a line from the fuel tank to the engine compartment (I ran one on my car). Somewhere along that line you would put the charcoal canister. From the canister you would come back to the engine for vacuum to suck the fumes in. The addition of a valve (or valves) so the ECU can control that is throwing me for a loop. Thanks!

[PeteKz]

I'm still thinking that the fuel fumes are coming from somewhere ahead of the firewall, because you are having the smell when driving down the road. Any fuel leaks in the engine bay that I've had, I could not smell when driving.

You said the overflow tank under the dash is not there--what did the PO do with the hoses? Are they butt connected to each other? Removed completely? IF so, what did they do to plug the old connections?

Open the rear tunnel cover and stick your nose in there and see if the fumes are stronger; also sniff at the front of the tunnel. If not, then I'm 95% sure it's somewhere up front. Keep sniffing. Sometimes it's not obvious, but you will know when you find it.

[dpegan]

I had a similar fuel smell in my stock 84 911 a few months back. Open the window and you smelled fuel and close it and not so much. Found out it was a fuel line leak on the rubber hose that connects to the fuel tank and snakes up over the steering rack than connects to the tunnel fuel line. The leak was small enough that fuel would puddle on top of the plate that covers the steering rack and fuel pump and then evaporate so there was no fuel visible under the car. Check the rubber fuel lines for cracks from the front fuel pump and tank to the tunnel lines.

[Duc Hunter]

Originally Posted by PeteKz

I'm still thinking that the fuel fumes are coming from somewhere ahead of the firewall, because you are having the smell when driving down the road. Any fuel leaks in the engine bay that I've had, I could not smell when driving.

You said the overflow tank under the dash is not there--what did the PO do with the hoses? Are they butt connected to each other? Removed completely? IF so, what did they do to plug the old connections?

Open the rear tunnel cover and stick your nose in there and see if the fumes are stronger; also sniff at the front of the tunnel. If not, then I'm 95% sure it's somewhere up front. Keep sniffing. Sometimes it's not obvious, but you will know when you find it.

The multiple PO's took everything out. Those lines are gone, the tanks are gone, and there was no evidence it was there before (car's been painted several times). I agree it's in the funk, and thats why I'm trying to set up a semi-proper evap system. The tunnel has no fuel smell at all, and the front of the tunnel, where the fuel lines go out to the tank is completely sealed up. So no air from there will get into the tunnel. I'm 99% sure it's from the charcoal canister I put in, thats in the Frunk, and does not have a hose venting its fumes into the intake.

Originally Posted by dpegan

I had a similar fuel smell in my stock 84 911 a few months back. Open the window and you smelled fuel and close it and not so much. Found out it was a fuel line leak on the rubber hose that connects to the fuel tank and snakes up over the steering rack than connects to the tunnel fuel line. The leak was small enough that fuel would puddle on top of the plate that covers the steering rack and fuel pump and then evaporate so there was no fuel visible under the car. Check the rubber fuel lines for cracks from the front fuel pump and tank to the tunnel lines.

All of those lines are new and are not leaking. I also ran new hard lines (plastic) downtime tunnel for both the feed and return fuel lines. So I am sure that not the issue. Hence why I'm trying to source a vacuum diagram.