1998 Ford Ranger passed the smog check pre-test, but failed the actual smog test... why?

I had a pre smog test done on my 98 Ford Ranger and it passed the test. When the real smog check was done again, it came up that it was a gross polluter. Why and how would it pass the smog pretest and not the actual smog check?

Answer:

We've heard of this happening before not identical to what happened to your 1998 Ford Ranger but where a vehicle passed the smog check pretest at a smog repair center after having repairs done, and then failed the smog test only at a smog test only center. It was described to us as a fluke in the smog machine system. No other description or explanation was given. We can only recommend you contact the BAR (Bureau of Automotive Repairs) regarding this incident, and in fact have a smog check repair station conduct a hands on diagnosis of your Ford Ranger's emission system to verify if the actual smog check result were in fact accurate and your Ford Ranger is polluting.

posted by SmogTips Support