Mysterious small green cap and a chugging Stang

mickn8r65

New Member
Aug 20, 2018
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Hello All,
First post so please be kind :)
I have 2003 Mustang manual transmission with a V6. I was looking for the AC recharge port when I came across this little green cap:
View media item 13797
I must have messed with it just enough to cause the car to chug violently in first gear. Less so in second and not at all above that. Any help on what it is, how I caused the problem and what I can do to fix?
Thanks in advance!!
 

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wmburns

SN Certified Technician
Aug 14, 2009
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Houston Texas
The green cap is the test port for the EVAP system. So if you messed with it and now have driveability issues it seems to me that you have created a vacuum leak.

NOTE, the EVAP test port has a left hand thread.
 

wmburns

SN Certified Technician
Aug 14, 2009
5,842
505
194
Houston Texas
Spray a lite mist of water on it to see if you can hear the vacuum leak. Once found, fix the vacuum leak.

NOTE: the EVAP system is pressurized only to 0.5 PSI. So if you applied any high pressure air to the EVAP system you have likely blown a seal some where in the EVAP system.
 
Last edited:

MattMan02GT

Active Member
Jul 24, 2018
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When you say messed with it, what did you do? Just take the cap on and off, or did you try to fill that line with coolant somehow?