Check for engine misfires, rough idle, hard starting, poor fuel economy, or loss of power
Listen for injector clicking with a mechanic’s stethoscope or long screwdriver
Inspect injector connectors and wiring for damage, corrosion, or loose plugs
Use an OBD-II scanner to check for trouble codes related to injectors or misfires
Measure injector resistance with a multimeter and compare to manufacturer specifications
Test injector pulse with a noid light or oscilloscope
Check fuel pressure and fuel pressure drop after shutdown
Perform an injector balance test with a scan tool or fuel pressure gauge
Inspect for fuel leaks, wetness, or fuel smell around injectors
Remove and visually inspect injector spray pattern if appropriate and safe
Clean or swap injectors between cylinders to see if the problem moves
Check fuel trim data on a scan tool for signs of lean or rich conditions
Confirm battery voltage and ground supply to the injector circuit
Have injectors professionally flow-tested if needed