# Fixed a gas leak but have compression building

**URL:** <https://community.cartalk.com/t/fixed-a-gas-leak-but-have-compression-building/36910>\
**Category:** Power/Fuel\
**Tags:** caravan, dodge, gas-tanks, gasoline\
**Created:** [September 20, 2009, 9:30pm UTC](https://community.cartalk.com/t/fixed-a-gas-leak-but-have-compression-building/36910 "2009-09-20T21:30:05Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![davidbcartwright](https://avatars.discourse-cdn.com/v4/letter/d/ecb155/32.png) [@davidbcartwright](https://community.cartalk.com/u/davidbcartwright)\
**Post date:** [September 20, 2009, 9:30pm UTC](https://community.cartalk.com/t/fixed-a-gas-leak-but-have-compression-building/36910/1 "2009-09-20T21:30:05Z")

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in-laws had a gas leak and had had the gas pump in tank repaired an the tank back on  
  
 then they began to leak as a drip  
  
 then it got worse  
  
 but only after the car had ran for a while  
  
 compression was evident upon removing the gas cap  
  
 i finally am in the area closing the three hundred plus mile gap only to see the van on car jacks  
  
 as it has been for two years  
  
 so in determining an assessment of the issue i drop the tank to find a line that led into the tank in front of the pump was diconected  
  
 seemed to be the source of the leak  
  
 put a hose clamp onit and reattached it and no more leak  
  
 however there still seems to be quite a deal of pressure beneath the gas cap when removed  
  
 it is a 93 chrysler 3.3 litre van  
  
 if that is any help  
  
 anybody know if this pressure is natural

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**Author:** ![Caddyman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/caddyman/32/23_2.png) [@Caddyman](https://community.cartalk.com/u/Caddyman)\
**Post date:** [September 21, 2009, 1:11am UTC](https://community.cartalk.com/t/fixed-a-gas-leak-but-have-compression-building/36910/2 "2009-09-21T01:11:49Z")

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It is indeed normal to have a slight amount of pressure in a fuel tank…2-3 psi. Before pressure builds further, an automatic valve ovens and allows the vapor to bleed off into the “carbon canister” where the hydrocarbon vapors are captured and are purged into the engine when it is operating…If this system is not operating correctly, the “check engine” light usually comes on.

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**Author:** ![davidbcartwright](https://avatars.discourse-cdn.com/v4/letter/d/ecb155/32.png) [@davidbcartwright](https://community.cartalk.com/u/davidbcartwright)\
**Post date:** [September 21, 2009, 1:41am UTC](https://community.cartalk.com/t/fixed-a-gas-leak-but-have-compression-building/36910/3 "2009-09-21T01:41:33Z")

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i’m not getting a chk light  
engine seems to be performing proper  
is the carcan directly linked to the tank?  
the line that was unhooked was in front of the modulator feeds in the tank  
how do i begin to check the lines or the canister  
is this something which is ecconical to replace?  
is this something that can operate without by drilling a hole in the gas cap (wich has been suggested)

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**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\
**Post date:** [September 21, 2009, 3:18pm UTC](https://community.cartalk.com/t/fixed-a-gas-leak-but-have-compression-building/36910/4 "2009-09-21T15:18:30Z")

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I think he computer diagnostics in a 93 model pre-date OBDII, so it won’t catch a problem in the EVAP system.  
I would leave it alone if there’s no check light, no leaking or smell of raw gas and no performance problems.  
Likely normal pressure just pushed off the loose, unclamped hose.  
Drilling a hole in the cap will disable the EVAP system, may cause the check light to come on, definitely release pollution, waste fuel and cause the remaining fuel in the tank to degrade over time.

p.s.: You’ll get more tank pressure in hot weather.