Engine/Transmission (1998.5 - 2002) Interpreting Smog check results

[VicR]

Had to smog the 99 for the first time (thanks Big Brother!). The Opacity reading was . 4%. That doesn't seem like that much to me. Heck I would have thought the ambiant air in Reno was more then . 4%



Was just curious how other's readings were and how my completely stock truck compared. My certificate says that was at 40 MPH on the Dyno.



-Vic

 

[A Johnson]

Since no one answered I will. Was talking with a fella at the transit authority that I service, and asked him just for curiosity what was a legal limit. He said they have to fix them if they are over 50%. Keep in mind this is older buses with mechanical fuel systems that are at these numbers. The newer buses are much lower but I don't know what the #s' are. I thought you might find this interesting for a reference if nothing else.



A Johnson

 

[krs]

In Washington state they require an opacity test in some counties every other year. For vehicles built prior to 1991 the limit is 50% (or 60%?) and for vehicles built after 1991 it's 40%.



As best I can tell this is sorta' like the percentile rating of the darkness of tint on glass. If so, then a reading of 40% means that the smoke from a vehicle's exhaust blocks 40% of the light that could pass through it. That's pretty dark and the way they conduct the test would make it real hard to fail because the reading is taken as an average over the range of RPM from idle to WOT.