A VW Passat was stopped in Bridgnorth Road, Wollaston, at 1am today, which had four men inside.
The men have been arrested on suspicion of theft after five catalytic converters, cut from vehicle exhaust pipes, were found in the boot of the car.
A 22-year-old scrap metal dealer from Brierley Hill, a 19-year-old man from Wolverley, a 22-year-old man from Dudley and a 25-year-old man from Halesowen remain in police custody for questioning.
Further searches will take place at their home addresses and any linked premises as part of the investigation.
There has been a sharp rise nationally in the number of catalytic converter thefts which has been fuelled by the increase in value of their precious metals.