Cranks no start low spark

I have a 2005 Altima 2.5s that I just changed the ECM on with a used one. Car has been running fine, even better with the new ECM. Went to the store, ran just fine, came out and it will crank but not start. Fuel pump is fine, changed the camshaft sensor and checked the fuses. It is getting spark but it seems very low. I have to cup my hand around a grounded plug and make sure it is in the shade to see a spark but there is one.