The starts and runs for a couple of seconds then dies is a symptom of the lack of a 50 hertz fuel enable signal. This signal comes from BCM and goes to PCM. Without the 50 hertz fuel enable signal, pcm will apply injector ground until car runs. Then will not supply ground because of lack of 50 hertz fuel enable signal, or messed up fuel enable signal.
The fuel enable signal is part of the vats security system. So I must ask, is your security light coming on when you turn key on, then staying on instead of going off after a few seconds? If yes you have a vats security problem.
Even if security light is cycling on then off normally, you could still have a problem with the 50 hertz fuel enable signal. I learned the lesson last summer on my 90 f-body. The security light only comes on if there is no 50 hertz fuel enable signal. If signal is wrong voltage and waveform, like my 90, security light does not light.
It took one of those $70 pc based oscilloscopes to diagnose my problem. The fuel enable signal was being sent out, however it was the wrong voltage and had a crazy waveform. The correct signal should be a nice rectangular waveform, occurring 50 times a second.