There are two ways to pick up an rpm signal during the smog. First is on the plug wire, second is if the smog machine is connected to the OBD2 connector under the dash. If the car is smogged with the OBD2 connector, there might be a problem due to the fact that the smog machine will access the PCM to check for any abnormalities. If you pick up the rpm on the plug wire, the smog test technician will have to tell the smog machine computer it's not hooked to the OBD2, thus it will not access the PCM. Do it that way. I can't tell you if it'll pass out the exhaust, probably depends on the card. dj