1998 evap service port

i've been pulling my hair out for the last several weeks trying to diagnose a Po442 code, evap small leak detected. after checking all possible leak sources, looked a second time under the hood and found a cap off of a part at the firewall. the tag read, evap service port-1 psi max. replaced the cap (similar to a tire stem cap) and have been cel free for approx 2 weeks. i can't find any info on this part, other than what's on the tag. any idea of it's function or does it have specific part name?

I believe that would be the schrader valve for the low side of your A/C system. The cap is just a dust cap to keep dirt out. Why the cel would clear after putting it on is anyones guess. Maybe the core is not seated properly and the dust cap is sealing it now. Is the A/C working OK?

the valve/port in question was labeled as a evap service port - as far as i know has nothing to do with the a/c, which is working fine. i cleared the cel with my handheld code reader. thanks for the input.

Sorry about that. I just "assumed" again. Looking into it further, Haynes says it is a system to capture fuel fumes and store them in a charcoal canister and then route them to the engine intake. I looked on my '99 and don't see one. Wonder what they did.

i had the charcoal canister off, located under the vehicle on the right side, if i remember correctly, centre. i'm sure that yours is still located there.

I believe, having never had to delve into the EVAP system diagnostics, that is a test port to check the system's integrity for emissions compliance.

Ford quote:

"The Evaporative Emission (EVAP) System Test Port is used to connect the Evaporative Emissions System Leak Tester to the EVAP system."

My son thinking he was helping out tried to recharge the AC on a 1999 chevy tahoe by hooking up the recharge refrigerant R134a to the evac port thinking it was the hook up port for the AC recharge. Any idea if this will cause a problem?
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