I have a 89 civic. It was swap with a 91 crx hf. The check engine light came on. It sort of stall a little then starts. I want to know what I should check.

i have a 89 civic. it was swap with a 91 crx hf. the check engine light came on. it sort of stall a little then starts. i want to know what i should check.
Found out the problem .code said 6. it was the coolant temp sensor. Expose parts on the wires were touching each other. So I separated it and the check engine light went off.. the I took it off the battery to reset the ecu

I've been having trouble with my 92 civic si and I tested the ecu for codes and my light just stayed on. I read that if the light just stays on that means I have a bad ecu. Is that true? How much is an ecu??