Took my 93 Ranger with 51k original miles to get smogged and it failed due to EVAP issue related to the gas tank not holding pressure. I have owned the truck since new and have had it smogged every two years here in CA without issue until now. I was very suprised by the failure as there where no CEL or anything like that to notify me there was a problem. In discussing the issue with the tech he stated the gas cap passed but the tank didn't hold pressure adequately. So I'm a little confused as to how you can have no CEL notification when you have a gas tank not holding pressure. I got underneath the vehicle to check the fill spout, purge (vent) line to the charcoal canister, see if anything is in disrepair but everything looks okay. I pulled a vacuum on the purge line where it connects to the canister but no vacuum was acheived. There is no smell of gas like a leaky ring seal, reached up on top of the tank and felt around, found nothing damp or wet. I was going to perform a smoke test on the tank / filler neck assembly to very any leaks. Any suggestions would be appreciated. What am I overlooking or not taking into consideration. The previous smog test was performed about 800 miles & 18 months ago without issue.

 

Get a friend and use a hose and your lungs to find the leak

Remove gas cap
Put end of hose in the filler wrap a damp towel around it to seal it
Blow into the hose
If there is a leak near by you will hear it
Have a friend listen at engine bay end

Do NOT use a compressor for this
Your lungs can generate maximum 2psi air pressure which can not blow off any fittings, air compressor can not go that low and WILL blow off fittings

1994 and earlier Rangers use the older EEC-IV computer which didn't always set emissions codes, it was primarily concerned with running the engine.
1995 and up used the EEC-V computer which monitored everything