Failed Emissions

I failed for HC- reading-517 standard-220, what causes high HC ? I changed the plugs, looked like they needed it. Put in E3’S,No codes coming pu. Any ideas?

First, what are “E3s”

High HC means too much fuel is passing through the engine unburned. Many possible causes; rich mixture from various causes, miss fire various causes, bad catalyst…

New diamond tech plugs, truck stalled one time, I pulled over & started the engine, then reved it up & it made a PAWOOSH sound all of asudden. Then ran fine.

I think the cat crapped out.