do 1998 Ford Ranger 6cylinder 4wd have 2 catalytic converters?

Yes. Some Ford vehicles, like v8 Mustangs, before 2005 had 4. Did the smog testers tell you to replace them? Sometimes a tune up, filters, and a good fuel system cleaner will take care of it.

Short answer-however many it came with WHEN NEW is what it will take to pass. They don't have to be OEM FORD parts, or installed in the exact original places, to clean up the exhaust enough, but they do have to be there. They also need to have the same relative places to install any original type O2 sensors, because without proper feedback from the O2 sensors the exhaust will default to a richer condition and you'll still fail. In localities that DON'T have mandatory emission inspections you can get by with practically anything that isn't too loud, but in jurisdictions that DO, its generally illegal TO SELL any vehicle that doesn't pass inspection. BUT someone in a place WITHOUT inspections can sell to someone in a place WITH them and the buyer then has to correct the vehicle on his dime. . If yours doesn't have 2 on it NOW and YOU didn't alter the exhaust, then someone ahead of you MUST HAVE. That's often done in the name of "performance" along with better flowing headers, and low restriction mufflers, or just for economic reasons, ETHER of the dual convertor sections of the setups on your truck are high buck items. And either could have been replaced with much cheaper non-convertor sections. I just checked. There are 2 different 2-catayltic convertor setups for your truck. BOTH use 2 convertors. Setup one has them both welded into the "Y" pipe coming off the manifolds Setup 2 has them inline with each other further down the exhaust path. The prices are comparable. (at Rockauto- there are a few choices in the mid $300's (for the 2-convertor piece) Just my opinion, but I figure that the first type is better protected by its location (being tucked up high) and would tend to not get damaged as easily as the second, which can hit things like rocks, if the truck gets overloaded and bottoms out or gets high-centered.