It works, just don't trigger it, and don't name it. Just place an env_smoketrail and compile and it'll show up ingame.
The problem is that i simply cannot change any of its properties, like the start and end color. Its just keeps grey ingame. Plus, there's no fire. Why is there a firesprite property when it is not showing any fire? Its just smoke.
I have an env_smoke, and that does exactly what i want: spray a constant stream of particles downwards. The only problem is that you can't specify a different sprite (fire sprite), it only emits smoke. If i was able to specify a fire sprite for the env_smoke, my problem is solved. And no, turning off SmartEdit and add the property and value manually doesn't work.
Stupid Valve and there's stupid limitations! All i want is a long exhaust flame, like this:
Is that too much to ask!? God.. damn! Fucking Source and its fucking entities not listening to what the mapper tells them to do!