If you’re into DIY auto maintenance, here’s a project for you. Fuel injectors are made up of a coil of wire which opens a valve when energized, basically an electronic solenoid valve. These can wear out and to diagnose them properly requires more than just applying 12 volts and listening for a click.
Dino, a professional auto tech by day, shares his circuit for a fuel injector tester. Requiring a 555 timer, N-channel MOSFET and a handful of supporting components, the tester sends a pulse to the injector allowing you to separately measure fuel output with a pressure gauge.
$20, that is pretty cheap.