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Official Curmudgeon
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4,707 Posts
Discussion Starter · #1 ·
Do the later CJs or YJs have a screw on gas cap or do they use the same quarter turn type cap? I put
a fuel injected engine in my CJ and had to do away with the vent to keep the tank pressurized. I didn't
use the purge valve and probably should have. Now I have the smell of gas around the cap and if I don't
get the cap on good, it will blow it off so I think I need the threaded type cap. Any other suggestions?


 
G

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Try a locking gas cap. Mine is great, I think I bought it at AutoZone it's one that you push on and it locks into position. It also has a rubber gasket for pressure release. Just a thought

 
G

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I'd reconnect the charcoal canister, and purge system. It takes no horsepower out of the system and it traps the raw gas fumes and reburns them in the engine while you drive. The later YJs and TJs have the screw in caps and filler necks and you probably could easily install them in your CJ if you have 2 large hoses to your tank (fill and vent). It sounds like you might not have any other vent on your tank, as the later CJ caps aren't pressure vented. Did you plug or disconnect the vapor separator/vent valves located in the left rear fender area? I'd try to return the vent system to the stock setup if possible. Hope this helps, goood luck.

 

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Official Curmudgeon
Joined
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4,707 Posts
Discussion Starter · #4 ·
As I understand it the tank needs to be pressurized since I installed a GM tuned port V8. The original
Jeep charcoal canister had to go because of the higher fuel line pressure (50 psi as opposed to 8 psi in
a carburetor system) and increased volume of fuel returned to the tank by the pressure regulator. I did
my homework before I installed the engine and everything I saw indicated I needed to get rid of the
canister. The original GM system had a computer controlled purge valve which released the pressure to
the canister but I think this is only after the engine is turned off. Everything said I could delete the
purge system with no problems. When I ordered the harness they also confirmed that I didn't need the
purge system. I may need to look into this a little more but with or without the purge system, the tank is
still slightly pressurized and I need a cap that will hold it.


 
G

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It doesn't matter if you have an EFI system on your vehice, nor how much pressure the system needs, you still must vent the tank. The purpose of the cannister is to separate and store the gas fumes from the vapor that is produced in the tank. The purge valve on the EFI motor is computer controlled to bleed this trapped fuel vapor into the intake system in a precise amount. If this feature is not present in your EFI system, and is not necessary for smog rules, you still must vent the tank to allow for normal expansion and contraction of the fuel. Pressure vented caps are available from Stant that you should be able to match up with your present filler neck. The older model vehicles produced before 1970 had this type of venting. You may get the smell of gas in the vehicle though if you drive with the rear window open. Hope this explains this system a little better, good luck.

 
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