Definitely don’t throw the old parts away. Replacing parts even is a relatively simple car like the Metro, with a modern engine like it has you can run out of money before running out of ideas.
Is the check engine light on? Have you checked for any stored diagnostic codes? If not, that’s the place to start.
When you say it fires when you prime it, do you mean you spray some starter fluid (like ether) into the intake manifold, then it starts ok, but only runs for a few seconds?
What makes you think the injector isn’t pulsing? Which injector? Just one of them? Or all of them?
I’m suspecting a heat sensitive electrical component. If it is sparking ok, but none of the injectors are firing, as the OP suspects, it could be the ground for the injector solenoids. Make sure that is solid connection to the chassis. If not that, it could be a bad relay or fuse in the fuel injector control circuitry. Those can fail when hot, but work ok when cold. You probably have a main fuel injector relay, so try tapping on that, see if it helps. Better yet, remove it and test it on the bench. If none of the above, check the connection at the ECM connector.
You might want to bring in a tech to help you diagnose this problem. Diagnosis a no-injector pulse condition really requires a lab scope to look at the injector control pulses.