My civic start for a sec then cut out main relay starts clicking when motor cuts out. Most the time motor won't start and main relay makes clicking sound when trying to start. I replaced the main relay and the ecm.

Try these steps:

. Check all under-dash fuses with a test light or multimeter:

https://www.askmehelpdesk.com/cars-trucks/faq-how-troubleshoot-repair-maintain-hondas-46563-3.html#post252145

. Clean the main ECM ground on the thermostat housing. Look for a 3-wire brass connector.

. Clean the 3-wire connector going to the MAP Sensor.