I just spend a lot of time setting up infrastructure for Ethylene production (in Mekanism) but now I can't pipe it into the Gas Turbine Generator...

Minecraft 1.11.2
BdLib 1.13.2.7
Advanced Generators 0.9.20.5
Mekanism 9.3.2.307
Forge 13.20.0.2315

Maybe related. Per wiki a Gas Intake Valve is required for Mekanism gasses. As of right now That item is not showing up in JEI or in creative mode. Not reimplemented Yet?
Playing:
Minecraft 1.11.2
All the Mods 2 V0.70
Advanced Generators 0.9.20.5
Mekanism 9.3.2.309

I know this post is months old, but just so you know; in order for ethylene to be used, it has to be turned into liquid ethylene via a rotary condensentrator.

This is for all the mods 3 version 3.3, Same issue as OP. Using gas intake and ethylene gas (converts to liquid via the generator) and it just sits there.

SS for proof:https://imgur.com/a/hSiO9

I'm closing this issue as part of a spring cleaning of my issue trackers from old stuff.

If you believe it's a bug that is still relevant in Minecraft 1.12 - Feel free to reopen it.