911sc Gas Tank Vent System

[sperberj]

Hi all; There are lots of threads on this one but I thought it needed a recent thread because the problem was so deceptive and difficult to diagnose and fix. Now that the work has been done it shoud be much easier to address. Here goes:

1. I found that there was still a gas smell after fixing all the hoses under the tank (this is a separate thread and fairly easy to address).

2. I checked the hoses to the expansion tank under the left driver fender and found they were corroded, and broken and venting to the outside air. (See Fig1)

3. I replaced these with hoses from the host and thought everything was fine so went for a test drive.

4. Stpped at a station to fill up and when I opened the tank there was a long exhale from the tank which was under a lot of pressure. This was pressure in the tank and not vacuum.

5. I then checked the vent hoses to see if they were all clear and found that they were except for the small vent line to the charcoal cannister in the back of the car.

6. So here is where it gets difficult.

6a. You will need to remove the left front wheel to replace those hoses if needed.

6b. Jack up the car onto ramps at all 4 wheels because you have to work under the car. The higher the better. Then be double sure that the car is safely up there with backup jacks

7. I replaced the small vent hose all the way to the tunnel which was quite a pain due to access difficulty.




8. I pulled the new hose through by connecting them using a cut bolt thread to hold them together (make sure they fit well). See next pic.



9. Then I thought it was fixed attached it to the tunnel line. Started up and thought I was good and the line was still blocked.

10. Checked the hard line going into the tunnel and it was completely clogged. I guess 40 years of bad gas will do that. See the extent of the blockage in Fig3.



11. Figured I could clear it with a wire. Nope, that thing was clogged completely for the first foot or so into the tunnel. Now completely removing this line requires an engine drop (really, dont try it any other way).

12. So I had to remove the seats (8 bolts..easy), remove the console and ac switches (separate thread), remove the rear access plate to disconnect shift shaft (just unscrew the allen screw nothing else), remove the gearshift assembly (separate thread easy) and voila........now you can try to find the vent line (not easy).

13. At the gearshift hole in the tunnel, I GENTLY bent the vent line and cut it with a dremel. Its a fragile line so be careful you have the correct line. Trace it from the front of the tunnel (be sure).




14. Once cut a got some steel wire (7 ft) and gently started it into the tube. I could feel the crystallized gas breaking up and used a plier to gently force it down the tube.




15. Whenever it got stuck I sprayed carb cleaner in there and let it sit about an hour. That seems to loosen the stuff. Also twisting the wire will loosen the stuff up. Patience is needed here and you only have about 4 to 5 feet to go ).

16. Every so often I pull the wire and spray the cleaner or acetone in there. Progress can be about 2-3 inches at a time.

17. Once you have gotten to where you think you are at the end of the pipe it is time to disconnect the vent to the carbon cannister at the hard line at the rear center of the car tunnel. Its hard to get to and has a clamp thats is pretty hard to remove. I used needle nose pliers to lever it off.

18. Go back and make sure the wire is all the way through and work it some more to loosen everything and then verify you can spray the carb cleaner through. I dragged the wire and sprayed a good 6-8 times and I could feel the line was smooth.

19. Verify you can blow through the vent line and attach the line from the gas tank vent. See Fig 6







20. So you should be connected from the tank through the tunnel to the outlet pipe and you are ready to connect to the cannister.

21. If the hose to the cannister looks good I would use needle nose pliers and a pre-attached new clamp to put on the vent hose. I use a new hose (be warned-the cannister is a pain to access also).

22. This solved the problem for me.

NOTE: If I had to do it over I would remove the cannister from the rear and mount it where I could easily route the line. It was truly a pain.

[evan9eleven]

Thanks for the great write-up. Wow, what a PITA job!

[gomezoneill]

I would've used a speedo cable attached to a drill. But nice work though.

[creaturecat]

nice write up, pics. thx

[isitivanorivan]

83 - 911SC Coupe—I was also surprised to see this setup when working on my car yesterday! After doing some heavy research and calling mechanic friends, they said these systems are essential to many cars.

The expansion tank (#3) is there if your car ever flips over and gas drains into the "expansion" tank. It's more of a safety tank than a true expansion tank.

Also, hose 6 was unattached and vented in my driver-side rear fender, which is a much better place for your gas to vent out to. You DO NOT want those fumes going back into your car. Before, most cars also had this venting into the rear fender.

If you haven't replaced all the hoses in a while, do so now. They get easily clogged. Imagine that going back into your car. Nope, vent into the fender. Happy Driving!!

[HarryD]

Originally Posted by isitivanorivan

83 - 911SC Coupe—I was also surprised to see this setup when working on my car yesterday! After doing some heavy research and calling mechanic friends, they said these systems are essential to many cars.

The expansion tank (#3) is there if your car ever flips over and gas drains into the "expansion" tank. It's more of a safety tank than a true expansion tank.

Also, hose 6 was unattached and vented in my driver-side rear fender, which is a much better place for your gas to vent out to. You DO NOT want those fumes going back into your car. Before, most cars also had this venting into the rear fender.

If you haven't replaced all the hoses in a while, do so now. They get easily clogged. Imagine that going back into your car. Nope, vent into the fender. Happy Driving!!

This is misleading.

Tank 3 is a wide spot in the line to allow the liquid fuel to separate from the air to have only fumes go to the charcoal filter.

Line 6 draws the fumes into the intake to burn them up.

This is a closed system.