Would a bad Cadillac converter make your van spit and sputter?

A bad catalytic converter can absolutely cause a van (or any vehicle) to spit and sputter, but it's not the only cause. A bad catalytic converter restricts exhaust flow. This backpressure can cause incomplete combustion, leading to rough running, sputtering, and potentially misfires. The symptoms you describe are consistent with a problem in the exhaust system, but other issues like a faulty ignition system, fuel delivery problems, or sensor malfunctions could also be responsible. A mechanic should diagnose the issue properly.