Whoosh! when removing the gas cap - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep CJ Forum > Whoosh! when removing the gas cap

FS: 2007-2013 Jeep Wrangler "HALO" Angel Eye KitTHE NEW! VANCO DUAL MODE 15/16″ Big Brake Kit w/BlaFS: Wranger BRIGHT License Plate LED! Just $3! Great value

Reply
Unread 07-17-2013, 04:28 PM   #1
adman02
Registered User
1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 278
Whoosh! when removing the gas cap

Here's my situation:

Jeep has been sitting in the garage while I slowly finish working on it. I decided to take the jeep to get some gas. I started it and let it warm up. Drove to the gas station (about 3 miles). Took the cap off and a strong whoosh of air came out of the filler hose. Tried it again when I got home and gas sprayed out.

So, why is this happening? And what can I do to stop it?

Here's my setup:
232 with Team Rush
Junkyard TBI
Running a gas canister (though it's a later model Jeep canister)
Also have a CTO controlling the purge signal*
I believe I have the OEM check and roll over valve

* I'm going to draw a diagram and take some pics of my setup in case that helps with the diagnosis.

adman02 is online now   Reply With Quote
Unread 07-17-2013, 05:35 PM   #2
John Strenk
Moderator
 
John Strenk's Avatar
1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 12,965
Wooshing out or in?

Either way, some vent is not working right. Do you have the hoses on the evap canister hooked up correctly?
John Strenk is offline   Reply With Quote
Unread 07-17-2013, 05:45 PM   #3
wellmax
Registered User
1984 CJ7 
 
Join Date: Nov 2008
Location: Hazel, KY
Posts: 1,068
I have an 1984 model jeep cj

still have the original gas cap,
no swish air noise when I uncap the fuel tank.

does your jeep have the funky fuel filter, one in and two out, the outside out to be mounted at (12:00 high).

on my jeep the outside hose goes back to the tank to vent fumes,

do you have problems starting the jeep after it sits a while, like a few hours or overnight?????

so I do not know if my tank get air from this return line or I have a vented cap,
the cap does not leak any fuel!!!!
wellmax is offline   Reply With Quote
Unread 07-17-2013, 07:46 PM   #4
adman02
Registered User
1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 278
Quote:
Originally Posted by wellmax View Post
I have an 1984 model jeep cj

does your jeep have the funky fuel filter, one in and two out, the outside out to be mounted at (12:00 high).

do you have problems starting the jeep after it sits a while, like a few hours or overnight?????
No. With the TBI, the funky fuel filter went away. Replaced with a fuel filter before the electronic fuel pump.

No problems starting the jeep. It starts easily cold or hot.

Quote:
Originally Posted by John Strenk View Post
Wooshing out or in?

Do you have the hoses on the evap canister hooked up correctly?
Wooshing out. Not sure about the evap canister. I THINK I do, but clearly something's not right.
adman02 is online now   Reply With Quote
Unread 07-17-2013, 08:20 PM   #5
adman02
Registered User
1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 278
Okay, here's my set up. BTW, no emissions stuff on the engine.

Click on the image to get to a larger one
adman02 is online now   Reply With Quote
Unread 07-18-2013, 04:20 AM   #6
John Strenk
Moderator
 
John Strenk's Avatar
1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 12,965
Take the green hose off going back to the tank from the evap canister and see if it still does it. If it stops then the problem is with the canister or hookup.
John Strenk is offline   Reply With Quote
Unread 07-18-2013, 06:17 AM   #7
keith460
Jeep. There's Only One
 
keith460's Avatar
1984 CJ7 
 
Join Date: Jan 2007
Location: Doylestown, PA
Posts: 4,722
Do you still have the Liquid and Roll Over Check valves installed at the rear of the Jeep. Not sure if 1979 had the Liquid Check valve though.



__________________
.
1984 CJ-7 Renegade
__________________

Restoration Thread:http://www.jeepsunlimited.com/forums...d.php?t=434226
keith460 is offline   Reply With Quote
Unread 07-18-2013, 07:39 AM   #8
adman02
Registered User
1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 278
Keith, I do have both valves:



I replaced my OEM evap canister with a more modern one...this one:


I followed the instructions listed here, but modified it to work with my TB (no bowl vent). But, looking back at this diagram, I wonder if I should have T'd my purge line to the PCV line rather than the Manifold Vac line.


BTW, I have a CTO that looks like the one pictured below (but with two ports, not three). Does it matter which port I plug the vac hoses into? I mean, if I swapped the hoses/ports would that make a difference in my setup?
adman02 is online now   Reply With Quote
Unread 07-18-2013, 07:48 AM   #9
keith460
Jeep. There's Only One
 
keith460's Avatar
1984 CJ7 
 
Join Date: Jan 2007
Location: Doylestown, PA
Posts: 4,722
How are the two vent lines out of the gas tank plumbed? They should BOTH go to the Liquid Check Valve and it doesn't look that way in the first photo you posted but hard to tell.

Purge line to the Charcoal Canister goes to manifold vacuum so it doesn't matter if it is T'd with PCV or not.

Is your CTO controlling vacuum to the Canister?
__________________
.
1984 CJ-7 Renegade
__________________

Restoration Thread:http://www.jeepsunlimited.com/forums...d.php?t=434226
keith460 is offline   Reply With Quote
Unread 07-18-2013, 08:01 AM   #10
John Strenk
Moderator
 
John Strenk's Avatar
1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 12,965
So did you drill out the plug on the canister the tank vent is connected to?




It shouldn't make a difference on a 2 port CTO which hose the vacuum line is connected to.
Hopefully it opens when hot and not close....
It should also be connected to a ported vacuum connection on the Throttle body and the Purge to the MAnifold vacuum or T into PCV line as you are thinking.
This is to keep it from opening during idle.



Just ignore the EGR section of these schematic.







this looks like the purge signal is also tied into your manifold vacuum. I can see an interesting flutter going on here....



More like this:
purgeandthrottlebody.jpg

John Strenk is offline   Reply With Quote
Unread 07-18-2013, 08:43 AM   #11
adman02
Registered User
1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 278
Quote:
Originally Posted by keith460 View Post
How are the two vent lines out of the gas tank plumbed? They should BOTH go to the Liquid Check Valve and it doesn't look that way in the first photo you posted but hard to tell.

Is your CTO controlling vacuum to the Canister?
I'll double-check the two vent lines when I get back home, but I believe they do both go to the LCV. It was hard to get a clear shot under there, so I just did a semi-blind point and shoot.

The CTO is controlling vacuum to the canister and ideally nothing else.


Quote:
Originally Posted by John Strenk View Post
So did you drill out the plug on the canister the tank vent is connected to?
I did drill out the plug.

Quote:
Originally Posted by John Strenk View Post
It should also be connected to a ported vacuum connection on the Throttle body and the Purge to the MAnifold vacuum or T into PCV line as you are thinking.
This is to keep it from opening during idle.
This could be the problem. I think I'm going to re-plumb in this way. It just seems to make more sense.


Quote:
Originally Posted by John Strenk View Post
this looks like the purge signal is also tied into your manifold vacuum. I can see an interesting flutter going on here....
That might explain why the idle rolls up and down on a cold start.

I'll plumb it like your last image and see what happens.

Thanks all for the replies. Vacuum lines are my Kryptonite.
adman02 is online now   Reply With Quote
Unread 07-18-2013, 03:50 PM   #12
adman02
Registered User
1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 278
Re-plumbed the engine to resemble your last diagram, John. The only difference is that I T'd the PCV/TB manifold vac/evap purge line together. Is that okay? The intake manifold vac (under the TB) is now just operating the brake booster.

Results - so so. The WHOOSH! turned into a pssst when opening the gas cap. That's an improvement, but there's still pressure building up.

Can someone explain what a ported vac line is? Do you think there's a conflict with having a ported line running to a CTO? Could I take the CTO out completely?

BTW, Keith, the two LCV vent lines do both go to the tank.
adman02 is online now   Reply With Quote
Unread 07-18-2013, 08:42 PM   #13
PERK
Senior Member
1983 CJ7 
 
Join Date: May 2007
Location: Castro Valley Ca
Posts: 612
wern't the older gas caps were vented? if yours isn't drill a small hole in it...cant do it here in cali.
PERK is offline   Reply With Quote
Unread 07-19-2013, 04:24 AM   #14
John Strenk
Moderator
 
John Strenk's Avatar
1976 CJ5 
 
Join Date: Feb 2005
Location: Shalersville Ohio
Posts: 12,965
ported vacuum is usually above the throttle plates so there is no vacuum when the throttle is closed. This is good because You don't need to have the purge line open enriching your mixture at idle or if there is nothing to purge, just creating a vacuum leak.

Same for the CTO, it wouldn't allow the purge to activate until the engine is warm enough otherwise it could cause too lean of a mixture.

Have you tried taking off the line to the tank to see if it still psssttt. That might narrow it down to canister or tank.
It could be the heat of the day causing the gas in the tank to expand also.
John Strenk is offline   Reply With Quote
Unread 07-19-2013, 06:51 AM   #15
adman02
Registered User
1979 CJ7 
 
Join Date: Jul 2008
Location: Durham, NC
Posts: 278
Quote:
Originally Posted by John Strenk View Post
Have you tried taking off the line to the tank to see if it still psssttt. That might narrow it down to canister or tank.
I haven't, but will do so today.
adman02 is online now   Reply With Quote




Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.