There isn't a single definitive "spark plug" because there are eight of them, one per cylinder. To know which plug goes where, you need a diagram specific to that engine's placement in the E-250. Your best bet is to:
* Consult your owner's manual: It will have a diagram showing the location of each spark plug.
* Use a repair manual: A Haynes or Chilton manual for your specific vehicle will have detailed diagrams and instructions.
* Use an online repair database: Sites like AllDataDIY or Mitchell 1 often have detailed diagrams (often require a subscription).
Remember to always disconnect the negative battery terminal before working on the ignition system.
