93 240sx losing 5 volt trigger to power transistor.

[largetacticaldrift]

Hey guys, I've searched and followed my fsm a million times now. After doing some trouble shooting I've discovered that my car is losing its 5 volt trigger to thethe power transistor after the car warns up. Everything is grounded properly and all components are within spec. The 5 volt wire spikes at idle randomly and then eventually just loses all voltage after a few minutes. Then the car won't start unless it sits for a while. Any advice?

[largetacticaldrift]

93 240sx losing 5 volt signal voltage to power transistor - YouTube (http://youtu.be/VyMYTOSuWCE) Here is a video of the car running until it loses the 5 volt trigger voltage and can no longer discharge the coil.

[largetacticaldrift]

2011 10 08 18 28 14 12 - YouTube (http://youtu.be/CE0xubKUfSg) This video is of the car in my shop, this is what it looks like when I lose the 5 volt trigger. I can only assume that the tach is jumping around because the transistor is failing to switch and you're seeing the failure throught the coil where it gets the tach signal. Please correct me if i'm wrong.

[largetacticaldrift]

Any ideas? Maybe another component is failing and causing the problem? Any input would be awesome