Question
Trying to get my 94 Corvette to run and have a crank no start. Have fuel (42psi at rail and injectors look like they are spraying properly), spark at plugs and 125psi of compression. No rpm is shown when cranking which leads me to think optispark but I have replaced it twice with no change. Also replaced the icm. It will occasionally fire up after sitting for at least 6 hours and run at idle for about 15 or die sooner and not restart for 4+ hours. If I shut it off after any amount of time it will not start for 4+ hours. Not sure what else to try. Any help is appreciated.
Answer
gcrankshaft position sensor (ckp) / wiring – optispark relies on ckp, no rpm signal could mean bad sensor or wiring. test for signal while cranking, check wiring for damage. ecm / icm wiring issue – if replaced optispark + icm but no rpm signal, ecm might not be getting ignition signal. check continuity between icm, optispark, ecm. check 12v power at icm + optispark. possible bad ecm. ignition coil / secondary ignition – weak spark could cause issues. test coil output, swap in known good coil if possible. fuel injector control issue – fuel pressure good, but injectors might not be pulsing. use noid light on injector connector while cranking. no flash = ecm not firing injectors. heat-related electrical failure – starts after sitting, could be heat-related failure (ignition coil, ecm, bad ground). test by cooling ecm/icm/coil when no start. optispark / aftermarket issues – some aftermarket optisparks unreliable. if not oem, might be bad. swap in known good oem optispark if possible. what to try next: test ckp sensor signal while cranking, check continuity in icm/ecm wiring (power + ground), use noid light on injector to check pulse while cranking, swap in different ecm if possible to rule out failure. let me know what you find. just get a better car.
