What type of injector is the 278-8317?
The number 278-8317 resembles Caterpillar fuel injector part numbering style (e.g., 276-8307, 317-5278, 263-8218), which are used on various CAT diesel engines.
Most of these part numbers refer to a fuel injector group for Caterpillar diesel engines, meaning the complete injector assembly that sprays fuel into each cylinder. For example, part numbers like 317-5278 are CAT fuel injectors for C10/C12/C13 engines.
Based on this pattern, 278-8317 is very likely a Caterpillar diesel engine fuel injector — a component that injects metered diesel fuel into the combustion chamber under high pressure.