Gas tank gets pressurized? - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

Reply
 
LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 09-24-2006, 03:13 AM Thread Starter
Enthusiast
 
RickCJ7's Avatar
 
Join Date: Sep 2006
Location: Longmont, Colorado
Posts: 277
Thanks: 0
Thanked 0 Times in 0 Posts
 
Gas tank gets pressurized?

Hi,
I am new to the BBS, and it sure looks interesting.
I have a 1984 CJ7 with I6 258 engine. Most trips I run into this problem and would like to find a permanent solution. This has been occuring for several years.

Pressure builds up in the gas tank. The result is eventually a poor running engine that won't idle due to the carburetor flooding. A couple of times I have had gas dripping out of the charcoal canister. There is often, but not always, an altitude increase involved. Home altitude is 5050 feet and I have gone above 11,000 feet. I have also had the pressure develop after 10-15 minutes of idling in my driveway, so maybe the exhaust pipe is heating the gas tank.

My temporary solution is to stop and loosen the gas cap every 20 minutes or 1000 foot elevation gain.

I described this to the local dealer. They said that they "blew out all the lines" and didn't find any problems. They also didn't fix the problem.

I studied auto repair in High School several years before this Jeep was born, but I do enjoy tinkering with it. I know that the fuel system is supposed to be a closed loop to control vapors from polluting the atmosphere, but somewhere there must be a vent to allow for expansion and contraction from heating and fuel useage.

Any ideas will be appreciated.
Rick
RickCJ7 is offline  
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 09-24-2006, 06:35 AM
 
Join Date: Apr 2006
Posts: 77
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Gas tank gets pressurized?

newer vehicle have a closed system and a solinoid assist's with venting

older carbed engine's didn't the vent was built into the gas cap
(engine started the system draws air through the cap into the tank and up through the vent line-canister-engine vacuum port

check the cap vent is stuck or you have the wrong cap(none venting)
here's a link check the system
http://www.autozone.com/servlet/UiBroker...23d801d7477.jsp
mazdab is offline  
post #3 of (permalink) Old 09-24-2006, 08:53 AM
 
Join Date: Feb 2004
Posts: 946
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Gas tank gets pressurized?

THis may help also


But your building up pressure as you go higher. I'd check the evaporator to see if it's working. Chanses are some of the hoses have been removed or are cracked and not working anymore. So nothing is relieving the pressure in the tank.
John_Strenk is offline  
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 09-24-2006, 09:23 AM
Way Outta Control
 
Join Date: Sep 1999
Location: The Palouse
Posts: 13,432
Thanks: 1
Thanked 3 Times in 3 Posts
 
Re: Gas tank gets pressurized?

Ok, let's be specific here... There's no way to build up pressure in the gas tank with a '84 CJ fuel system; unless you've hooked up a compressor to pressurize the tank. That means that you've got a negative-pressure in the tank. A negative-pressure translates to a vacuum. That's produced by the fuel pump removing fuel, and no air being able to get into the tank to replace the lowered fuel volume, hence the vacuum.

If the emissions systems are not working correctly, then it will not draw off the fuel vapors in the tank to the carb. If that's not working fuel mileage will suffer and likely the engine's being run rich.

Go here (click on the graphic):



or here (same information): A Primer on the Jeep 258 with Carter BBD & Pulse Air Emission System

Also, Mosel Ludel's book: Jeep CJ Rebuilder's Manual, 1972 - 1986, has 20 pages on repair of the BBD Carb system. The book worth the money to any CJ owner who wants to keep the CJ on the trail or road running reliably.
LEVE is offline  
post #5 of (permalink) Old 09-24-2006, 10:44 AM
I Might Just Know What I'm Talking About
 
Raduckal's Avatar
 
Join Date: Sep 1999
Location: Owensboro, KY
Posts: 1,905
Thanks: 3
Thanked 4 Times in 4 Posts
 
Re: Gas tank gets pressurized?

[ QUOTE ]
Ok, let's be specific here... There's no way to build up pressure in the gas tank with a '84 CJ fuel system

[/ QUOTE ]

That's a bit dogmatic.
If the man says it's so I would believe him, after all, we've all seen Jeeps to some odd things. I've had oil move up hill from the transfer case to the tranny. Something cloged, some thing acting like a one way valve... who knows...

I think the easiest fix would be a vented cap.
Raduckal is offline  
post #6 of (permalink) Old 09-24-2006, 03:08 PM
Way Outta Control
 
Join Date: Sep 1999
Location: The Palouse
Posts: 13,432
Thanks: 1
Thanked 3 Times in 3 Posts
 
Re: Gas tank gets pressurized?

[ QUOTE ]
...That's a bit dogmatic....If the man says it's so I would believe him...

[/ QUOTE ]

It's not dogmatic to teach or ask for proper principles, meanings and terminology; nor to point out such errors. Its done to neither demean or belittle, but a spirit of encouragement and edification. When concepts are not understood nor make sense then proper answers can not be given.

Do I believe the tank was being pressurized? Nope.. and said why in my reply. Does oil drip up the part? Nope, but draft when moving will blow the oil up the part. If I believed otherwise then I'd also believe Vince Foster and Admiral Boorda both committed suicide.
LEVE is offline  
post #7 of (permalink) Old 09-24-2006, 03:26 PM
I Might Just Know What I'm Talking About
 
jdoggmoney's Avatar
 
Join Date: May 2003
Location: Nebraska
Posts: 1,806
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: Gas tank gets pressurized?

I had this same problem for some time with my 79. Except other than the fuel supply line to the front, other lines had been removed or broken by the PO. I also had to replace the tank and when I did I tapped into one of the small vent tubes where the lines to the rollover valve would attach. I ran soft fuel line to the engine compartment, then up high with a plain jane fuel filter to keep dirt out. Hasn't pushed out any fuel since.

By the way, I'm not comfortable with switching to a vented cap, because my fuel filler is under water a lot. Also, I noticed that this only occurred when I filled the tank completely (maybe no room for exapnsion in summer heat). If I watched closely when fueling and didn't completely top off the tank it wouldn't occur.
jdoggmoney is offline  
post #8 of (permalink) Old 09-24-2006, 04:24 PM
I Might Just Know What I'm Talking About
 
Raduckal's Avatar
 
Join Date: Sep 1999
Location: Owensboro, KY
Posts: 1,905
Thanks: 3
Thanked 4 Times in 4 Posts
 
Re: Gas tank gets pressurized?

[ QUOTE ]
Do I believe the tank was being pressurized? Nope..

[/ QUOTE ]
I do, because that's what the man said and I try to keep an open mind.
It seemed a little insulting, unlike the LEVE I feel I know.
Raduckal is offline  
post #9 of (permalink) Old 09-24-2006, 06:28 PM
Way Outta Control
 
Join Date: Sep 1999
Location: The Palouse
Posts: 13,432
Thanks: 1
Thanked 3 Times in 3 Posts
 
Re: Gas tank gets pressurized?

I'm still the LEVE you know, but I don't understand what's insulting by saying: [ QUOTE ]
Ok, let's be specific here... There's no way to build up pressure in the gas tank with a '84 CJ fuel system; unless you've hooked up a compressor to pressurize the tank.

[/ QUOTE ]

It is true that I've neglected to think of fuel expansion on a hot day as pressurizing the fuel tank. That's a good point.
LEVE is offline  
post #10 of (permalink) Old 09-24-2006, 09:33 PM
I Might Just Know What I'm Talking About
 
Raduckal's Avatar
 
Join Date: Sep 1999
Location: Owensboro, KY
Posts: 1,905
Thanks: 3
Thanked 4 Times in 4 Posts
 
Re: Gas tank gets pressurized?

I'm just saying strange things are possible.
Maybe I was over sensitive.
Could someone come by and check me to see if somebody slapped an estrogen patch on me?
Raduckal is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome