This is just not a typical problem you encounter all the time and can throw you way off into the sunset trying to trouble shoot.
Back in the late 80,s when my brother was working for GM OEM had bad problems with the Corvette passing emissions, all the engineers couldn't figure out why and we discovered that high speed test were being done at 2500 rpms and failed all the time and what was happening was the AIR system was being turned off at 2500 rpms and would fail. CPU,s were then reprogramed at 3000 and all the cars passed. LOgic and that's why I am so crazy to understand why this problem happens.

 

there's no 5V anywhere outside the innards of the ECU and ICU. the injector output of the ECU is an 'open collector' NPN transistor, this selectively grounds (0V) or floats (12V because thats the supply voltage to the injectors via the 'radio suppression' relay. The output of the power module to the coil is much the same, the ignition power module is like an amplifier that takes the small current signal from the ICU and selectively grounds the coil pin 1, then floats. when its grounding pin 1, there's current through the coil primary, this builds a magnetic field up, when pin 1 is 'disconnected' (floating), then that magnetic field collapses and triggers the high voltage pulse from the coil secondary which makes the spark happen.

 

some how then the amplifier then is pulling down the 5 vdc because of the load the coil is putting on it . I changed that as well with no results.

 

measuring this 5VDC, which pins of what are you connecting the voltmeter + and - leads ? be specific about what ground (-) you're using. under what engine conditions (idling, cranking, turned on but not started or ?)

a typical OC (open collector, thats an electronics term/concept) output will be 0.6 or 1.2V when its switched 'on' (low, its inverse logic). but one thats constantly switching on/off could look like around 5VDC because its a square wave from 12V to 1.2V and back, with a duty cycle.