Vapor return line setup/ Tank pressure - Team Camaro Tech
Tech 2002 General Tech questions from 2002
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post #1 of 12 (permalink) Old Apr 16th, 02, 09:53 AM Thread Starter
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Eric
 
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How does the vapor return line get connected? Does it connect to the carb or the fuel pump. When I fill up with gas i seem to be getting pressure in the tank. I don't think this is a good thing. When I take the cap off the pressure in the take almost blows the cap out of my hand. Will the vapor return line help or is there a venting cap for a '69 camaro?

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post #2 of 12 (permalink) Old Apr 16th, 02, 11:10 AM
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It get's connected to the fuel filter, mounted just behind the water pump. Need the original A/C filter to make the connection.


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post #3 of 12 (permalink) Old Apr 16th, 02, 11:42 AM
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Mark is there any way to work around that with a non original engine?

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post #4 of 12 (permalink) Old Apr 16th, 02, 01:28 PM Thread Starter
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Yeah ah, my car never had A/C. Now what? Is there another way to release some of the pressure that builds in my gas tank?

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post #5 of 12 (permalink) Old Apr 16th, 02, 03:29 PM
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Mark was saying that you need the correct AC (brand) fuel filter with the extra nipple on it for the return line - Rick's has them. You also need a vented cap; Rick's has them too.

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post #6 of 12 (permalink) Old Apr 16th, 02, 05:11 PM
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JohnZ,

I have the original set-up with the vent line, etc. in my '69 RS/SS-396. I, too, get pressure build up in the tank. I bought a new vented gas cap, but it still has a release of pressure when I remove it at fill-up time. Any idea why this is happening?
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post #7 of 12 (permalink) Old Apr 16th, 02, 07:32 PM
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David Pozzi
 
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There should be pressure in the tank. The cap is set to hold back pressure to prevent loss of fuel vapor.
Your garage would fill with flammable fuel vapor on a hot day, if the cap were not a pressure type.
David

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post #8 of 12 (permalink) Old Apr 17th, 02, 11:10 AM
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I agree David but mine goes pee pee on the floor from the top of the tank unless you open the cap when you decide to stop for a while.

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post #9 of 12 (permalink) Old Apr 17th, 02, 05:36 PM Thread Starter
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Eric
 
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So pressue in the take is normal and won't cause any problems then?

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post #10 of 12 (permalink) Old Apr 18th, 02, 04:13 AM
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My tank has always released 'some' pressure when I go to fill up again, but it never smells in the garage either using the standard vented cap.
My extra fuel line is capped off with rubber hose bent over near the frame area with hose clamp over that. Previous owner changed my carb. from Rochester that it came with, to Holley which only uses one fuel line.
If I ever change back to Rochester I would re-connect the extra line and use the AC filter. It has one entry pipe nipple on the bottom for the 1st fuel line to connect to, it then has 2 pipe nipples on top, one goes to the carb, the other turns 180 degrees and drops back down to the 'return' fuel line.
click


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post #11 of 12 (permalink) Old Apr 18th, 02, 04:13 AM
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There was a thread a while back about this. I thought I would post an update for the board. First, the problem with my car was the tank would build vacuum and partialy collapse the tank if I drove around for a while due to the gas leaving the tank and no way for air to get in to replace it as the gas was used up. I do not have a vapor return line on my car. The "vented" gas cap was not working properly so no air would get in. I had the cap cleaned and it now works.

Now for the people who have the opposite problem of too much pressure in the tank, you may also have a defective "vented" gas cap. Here is what "I think" is happening. Gasoline is stored under ground in huge tanks that are cool as any ditch digger will tell you. Gasoline will go from the cold ground and into your cars above ground tank. The abient air temperature will raise the temperature of the gas which is now trapped inside your cars tank and cause it to expand. The expansion will cause a build up in pressure and that is why your cap "blows off" when you unscrew it or you get gas blowing out at rest. I did a problem as homework on the thermal expansion of gasoline when I was in engineering school. The question was "will the gas tank overflow after you go right home from the gas station after filling up. The answer was yes due to the thermal expansion of the fuel.

If you have your vapor return line properly hooked up to the correct filter and the cap is working as intended, these problems should not happen. If you still get overflow even with a half tank of gas that is the same temp as the air, then something else is wrong.

We need to collectively figure out these issues. Mine was giving me problems for years.

Just some rambling observations to consider.

-Mark.
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post #12 of 12 (permalink) Old Apr 18th, 02, 08:33 AM Thread Starter
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Thanks for the info on fuel expansion. I'll try hooking my vapor return line when I get a new fuel pump. I just didn't want my tank exploding on me. Here in Arizona the heat is so great fuel expansion would be a bigger problem.

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