it is deffenitly not your ECU. It does sound like it could be your crank sensor due to the fact you have a running HEI.Also in most cases ive see when your cps goes it will not throw a code, go figure. To test to see is thats your problem or not, put your car in CEL MODE TEN & GRD jumper. Then see it it will start that way. If it does start then its cps also your fans will be running when you open throttle. Which I have a spare cps