Hyundai Sonata LF: Engine Control System / Injector Troubleshooting
The three waveforms below are taken from the #1 and #4
injectors. The top waveform is from the high side (feed side) of the #1
and #4 injectors, while the middle waveform is from the low side (ground
side) of the #1 injector and the bottom waveform is from the low side
of the #4 injector.
The middle waveform is the same as the top waveform because
there is no ground for the circuit. With no current flowing in the
circuit, the #1 injector is not energized and fuel does not flow.
The bottom waveform shows that ground is supplied and there
is a voltage drop across the #4 injector. With current flowing in the
circuit, the #4 injector is energized and fuel flows.

Other information:
Description
The GDI injector is similar to a standard injector, but
sprays fuel at a much higher pressure directly into the combustion
chamber and has a swirl disc to get the fuel swirling as it exits the
nozzle. This aids in atomization of the fuel...
Removal
1.
Turn ignition switch OFF and disconnect the negative (-) battery cable.
2.
Remove the crash pad lower panel.
(Refer to Body - "Crash Pad")
3.
Remove the knee air bag.
(Refer to Restraint - "Knee Airbag(KAB) Module")
4.
Disconnect the stop lamp switch connector (A), and than remove stop lamp switch...