Chevrolet Repair: 1990 Camaro RS: Intermittant no start, 1990 camaro rs, grounding light

Question
I tested no spark via Alldata flow chart. When I had no start, test light in tach connector flashes, whether grounded or to power. This indicated to me the pickup coil in distributor was triggering the ICM in dist to ECM. As this cas has 331,350 miles, I replaced ICM, referring to chart, and dist cap, rotor, and coil for PM. Engine turns over but does not start, R/R ECM to test EST and reference values with labscope. When cranking, purple/white ref waveform is at 5. V and white EST waveform is at .75Volts and ECM case is hot and test light is illuminated when grounding light to ECM case to ECM battery power (orange wire BB1 or BC16 terminals) Is ECM case shorted internally? When engine runs, EST waveform is close to 5Volts. Thanks

Answer
HI STEVE, WOW, YOU HAVE DONE SOME HOMEWORK !!!! I DO NOT HAVE ANY FLOW CHARTS WITH ME AT HOME, BUT FROM WHAT YOU ARE TELLING ME THE ECM HAS LOST ITS GROUND CIRCUIT OR AS YOU SAY IT IS INTERNALLY SHORTED WHICH WOULD EXPLAIN INTERMITTANT NO START PROBLEM..CAN YOU CHECK YOUR FLOW CHART AND SEE WHERE IT GETS ITS GROUND FROM ???? THIS MAY SOUND CRAZY,, BUT I HAVE SEEN THE BODY TO FRAME GROUNDS CAUSE THIS TYPE OF PROBLEM.. I CAN NOT THINK BACK THIS FAR TO REMEMBER IF THIS GETS ITS GROUND FROM THE CASE TO GROUND OR IS THERE A WIRE IN THE HARNESS PLUG THAT GROUNDS THIS. YOUR TEST LIGHT SHOULD NOT LIGHT WHEN TOUCHING THE CASE.THIS FOR CERTAIN IS NO GROUNDING CONDITION OR INTERNAL SHORT. HAVE YOU TRIED EXTERNALLY GROUNDING THE CASE ?? AROUND MY AREA CORROSION WILL TAKE THESE OUT..THIS ALWAYS BEEN A TEXAS CAR ???  AS FAR AS THE 5 VOLT WAVE FORM WHEN RUNNING THIS IS GOOD.. WOULD LIKE TO KNOW HOW YOU MAKE OUT WITH THIS. GET BACK TO ME AFTER CHECKING THIS...