canster purge line & gas cap

pedal2themetal · May 15, 2021

Hi All,

Working on my 75 Fury.

Slight problem .. I re-ran the purge line. I put it into the air filter housing, but I am getting heavy vacuum in the tank when taking the cap off.. the cap does NOT say vented.. it does say take off slowly due to possible fuel spray. It is a new cap install by a shop and maybe its the wrong type?. I am afraid I am causing excess vacuum for the fuel pump to pull fuel.. Should I get a vented cap? or is the canister plugged (canister only has 2 lines on it one from tank other (purge) to air filter)? When looking one up on AutoZone it says vented..

Only 76,000 miles on the car.

Thanks All
Tim

steve340 · May 15, 2021

There is always a way of venting the tank in some way or another.
Not sure how your car is set up but the should be no vacuum or pressure building up in the tank in any case.

YY1 · May 16, 2021

Did you have the cap issue before the work to the purge line?

If so...

Does your car have a vent manifold near the tank like a 72-73?

My 73 had the shuttle valve stuck, and caused a very similar issue.

For the record, my purge line is connected directly to the purge valve on the float bowl.
I don't have all of the vacuum valve pieces in working condition to operate the charcoal can correctly.

That hasn't been an issue that I'm aware of.

pedal2themetal · May 16, 2021

HI YY1.
. The carb I have on it now has no purge valve connection.. (4bbl) I had the Purge line plugged off for a long time and don't remember any issues with the cap..But then the issue showed up. I had a leak at the tanks rubber hoses .. then I think after the fix the issue showed up.. (shop did the fix as well as the new cap).. that's when I moved the line to the air filter,. Where is the shuttle valve located?

Thanks
tim

YY1 · May 16, 2021

On a 73 it's inside a manifold in front of the tank that the vent hoses from the four corners connect to and then one line goes to the engine bay/charcoal can.

In 74 it's inside the tank. Yours might be there to. IDK past 74.

I guess you could try plugging the vent to see if the issue goes away.

mrmolding · Aug 6, 2023

YY1 said:
On a 73 it's inside a manifold in front of the tank that the vent hoses from the four corners connect to and then one line goes to the engine bay/charcoal can.

In 74 it's inside the tank. Yours might be there to. IDK past 74.

I guess you could try plugging the vent to see if the issue goes away.

I know this is an old thread, but how did you determine that the shuttle valve was stuck? Did you remove it and shake it or test it somehow? Wondering if I can remove the hoses and spray something inside to free it up if that's my problem. I recently started getting fuel spray and a whooshing sound when removing the cap and I have the pressure gas cap that is supposed to be correct for the car (I think). Looking for an easy fix before I start taking things apart. Thanks!

YY1 · Aug 6, 2023

mrmolding said:
I know this is an old thread, but how did you determine that the shuttle valve was stuck? Did you remove it and shake it or test it somehow? Wondering if I can remove the hoses and spray something inside to free it up if that's my problem. I recently started getting fuel spray and a whooshing sound when removing the cap and I have the pressure gas cap that is supposed to be correct for the car (I think). Looking for an easy fix before I start taking things apart. Thanks!

Yes, you should hear it slide back and forth.

Mine did not.

mrmolding · Aug 6, 2023

Thanks! I got inventive and hooked up a mini vacuum cleaner to the line from the separator manifold at the tank to the other end at the canister and felt air out of the tank filler neck. So I guess it’s not stuck.

canster purge line & gas cap

pedal2themetal

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steve340

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YY1

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pedal2themetal

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YY1

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mrmolding

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YY1

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mrmolding

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