WI case law has long held that the odor of burning marijuana alone (even without a loud muffler) is sufficient reasonable suspicion to allow temporary detention of a suspect for further investigation. However, any traffic violation would suffice for this, including loud exhaust. After they detained you for suspicion of drug use or the muffler, the officers would also be free to pursue leads as to different crime, such as taking alcohol tests, if they smelled alcohol (including forced blood draws at a hospital). However, if you indeed performed well in all of the field sobriety tests, their level of probable cause to continue holding you may have diminished after they failed to find any drugs. They had a legal obligation to release you as soon as you were cleared of all reasonably suspected crimes. You therefore may have a better than average chance of winning a motion to suppress the alcohol test, so you should definitely contact an experienced criminal lawyer as soon as possible. My comments in this public web forum are intended only for public educational purposes and are not legal advice specifically tailored to you and your case. Instead, you should retain a lawyer in order to meet your legal needs, since I will be taking no action on your case. Disclosure of confidential information in a public web forum is not recommended and is always subject to being used against you in court. You are welcome to contact my Racine, WI office at 262-633-3090 or email me at nixon@execpc.com for further information. Web forum answers may contain attorney advertising materials.