What does a good fuel injector waveform look like?
Short answer: On a typical port injector you see battery voltage at rest, a sharp drop near zero when the driver turns on, then a tall inductive spike when it turns off, often with a small hump that shows the pintle closing.
A saturated port injector waveform is one of the most useful patterns to learn. Before the event, the injector side sits near battery voltage. When the computer grounds the circuit, the voltage drops to near zero for the on-time. When it releases, the collapsing magnetic field creates an inductive spike, often 60 volts or more, before settling back to battery voltage.
That spike and the small bump that follows it tell you the coil and pintle are working. A missing or weak spike can mean a shorted winding. A long on-time compared with other injectors means the computer is correcting for something.
Adding a current probe shows the current ramp, and the pintle opening often appears as a small notch. Direct injection and diesel injectors work very differently, using high voltages and peak-and-hold drivers, so follow the maker's test procedure and never probe high-voltage injector circuits without the proper leads and precautions.
Tools used for this job
General guidance only. Follow the vehicle and tool manufacturer's procedures, and confirm vehicle coverage on the tool maker's list before buying.