Excessive gas tank pressure - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
LinkBack Thread Tools Display Modes
post #1 of 11 (permalink) Old Feb 19th, 06, 06:18 PM Thread Starter
Tech Team
 
Join Date: Oct 2005
Posts: 31
Excessive gas tank pressure

I just purchased a recently restored 69 big block. Yesterday after a short drive I heard a strange noise coming from the rear of the car. I isolated it to the gas tank. I started to remove the gas cap and was very surprised to have the cap shoot out of my hand and go back about three feet! I was almost knocked over by the pressure release. What is going on? The cap says it is "vented", but it sure fits tight. Any thoughts?
Cossack Warrior is offline  
Sponsored Links
Advertisement
 
post #2 of 11 (permalink) Old Feb 19th, 06, 07:32 PM
Senior Tech
 
Join Date: Jun 2005
Location: Sunny So. Cal
Posts: 3,064
Re: Excessive gas tank pressure

Try replacing the cap. It might be bad.

67 RS Camaro 327/ 350 Holley 650cfm > Edelbrock Performer Intake > Pertronix Ignition > Accel Super Stock Coil and Wires > Hedman Hedders > Hotchkis Performance Springs > 15" Rallys all around

Camaro buds until the end!!!
Camaro Dave is offline  
post #3 of 11 (permalink) Old Feb 20th, 06, 04:39 AM
Super Moderator
Jake-68's rule
 
Everett#2390's Avatar
 
Join Date: Sep 2000
Location: Va Beach VA
Posts: 29,246
Re: Excessive gas tank pressure

The cap is vented, but to allow air to "enter" the tank as fuel is used.

If tank is pressurized, the exhaust is heating up the fuel tank, thus building pressure inside. Gas cap is a one-way valve, let's air in, but not out.

Give a man a rescued dog for the health of both their souls.
'With age comes wisdom, but then wisdom ages you even more.' GO CUBS! Other Stuff
Everett#2390 is offline  
post #4 of 11 (permalink) Old Feb 20th, 06, 10:35 AM
Senior Tech
 
Join Date: Mar 2004
Location: Valley Center, CA
Posts: 365
Re: Excessive gas tank pressure

I have been working on the same problem. I have 2 new GM gas caps, both work the same. They have a 2 way valve that allows air in as gas is used, and they vent out excessive pressure. You can check by blowing hard on the center hole inside of the cap. I am trying to determine that release pressure in P.S.I. I guess about 5 psi. But it is not low enough because it causes the car to cut out a little under load when it pressurizes. The valve can be moved to one side with a small nail and it will prevent pressure build up, but will also allow gas fumes to escape-not good. So I am working on a way to lower the release pressure in the valve.

69 SS350 ZL-2 4 speed, original paint, unrestored -SOLD

1972 AMX 401ci, 4 speed, cowl induction, console, gauges, posi, A/C, unrestored original
OAKLYSS is offline  
post #5 of 11 (permalink) Old Feb 20th, 06, 11:52 AM
Senior Tech
 
Join Date: Jun 2005
Location: Sunny So. Cal
Posts: 3,064
Re: Excessive gas tank pressure

Be careful and don't overlook the gas cap when it comes time for a Smog check. They will fail you for that and charge you a $59.00 rip off fee.

67 RS Camaro 327/ 350 Holley 650cfm > Edelbrock Performer Intake > Pertronix Ignition > Accel Super Stock Coil and Wires > Hedman Hedders > Hotchkis Performance Springs > 15" Rallys all around

Camaro buds until the end!!!
Camaro Dave is offline  
post #6 of 11 (permalink) Old Feb 21st, 06, 09:14 PM
Senior Tech
 
Join Date: Dec 2003
Location: Leander, TX
Posts: 2,765
Re: Excessive gas tank pressure

A little pressure is normal. You don't want fumes or fuel to escape.

If it's balooning your tank, you have problem and Everette (above) is probably right about the exhaust causing the trapped air in the tank to expand.
Straight-line-69 is offline  
post #7 of 11 (permalink) Old Feb 28th, 06, 12:58 PM
Tech Team
 
Join Date: Jan 2001
Location: Bloomington, Mn US
Posts: 31
Re: Excessive gas tank pressure

I have had the same problem with my 69 Big Block
Camaro and Nova. New gas caps made no difference.
The pressure would either leak out the tank at the
fuel line entrance or out the top of the tank at the
sending unit. Made no difference that tank wasn't
full. I guess it could be heat from the exhaust.
It can really make a mess.
I am at the point that I may drill a small hole in the
cap to see what happens.

Sully.........

69 396 Camaro<br />69 427 Camaro<br />69 396 Nova
Sully is offline  
post #8 of 11 (permalink) Old Feb 28th, 06, 09:22 PM
Senior Tech
 
Join Date: Dec 2003
Location: Leander, TX
Posts: 2,765
Re: Excessive gas tank pressure

Sully,..a hole in the gas cap will surely leak fuel, especially on acceleration when fuel moves to the rear of the tank. Sounds like you'd add another leak to the one you have on top of your tank,..which is likely a bad or mis-aligned o-ring for the sender.
Straight-line-69 is offline  
post #9 of 11 (permalink) Old Feb 28th, 06, 11:40 PM
Tech Team
Anthony
 
Join Date: Feb 2006
Location: The OC, CA
Posts: 68
Re: Excessive gas tank pressure

Yeah, this is a common problem - happens on my car all the time - the above is true about it being a one-way valve, the crossflow muffler heats the gas in the tank and it builds up pressure; shouldn't be too big on an issue if you release it every once in a while (after each cruise) - this is just something I think you (and I/us) have to live with... if you drill a hole in it you'll certainly have a gas trail following you... ever seen The Coyote carrying a bag of gunpowder?... it'd be like that...

Anthony

69 72B 711 L35/M40 Convertible Dad bought it new - 454 & TKO in now.

69 71 71 711 L34/M40 Coupe - endura / radio delete one owner barn find, POP & 3 Broadcast sheets! cool old drag car, never titled - odo shows 00455! 427 & TKO in now.

Other rides: 91 454SS and a 92 Brand X 5.0
Anth is offline  
post #10 of 11 (permalink) Old Mar 1st, 06, 07:54 AM
Senior Tech
 
Join Date: Mar 2004
Location: Valley Center, CA
Posts: 365
Re: Excessive gas tank pressure

The gas caps are a 2 way valve-you can check this yourself by blowing thru it from the inside of the cap. It just has too high a release pressure.

69 SS350 ZL-2 4 speed, original paint, unrestored -SOLD

1972 AMX 401ci, 4 speed, cowl induction, console, gauges, posi, A/C, unrestored original
OAKLYSS is offline  
post #11 of 11 (permalink) Old Mar 1st, 06, 11:41 AM
Senior Tech
 
Join Date: Jul 2005
Location: California
Posts: 2,353
Re: Excessive gas tank pressure

Quote:
Originally Posted by Camaro Dave
Be careful and don't overlook the gas cap when it comes time for a Smog check. They will fail you for that and charge you a $59.00 rip off fee.

smog checks dont go back past 76, here in cali
so both you and i dont have to worry about it
400bird is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Team Camaro Tech 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.
NOTE we receive a lot of registrations with bad email addresses. IF you do not receive your confirmation email you will not be able to post. contact support and we will try and help.
Be sure you enter a valid email address and check your spam folder as well.



Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



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



Posting Rules  
You may post new threads
You may 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