So I bought a new ecu for my 2000 prelude after figuring out it wasn't sending signal to the CKP. Have new ECU and volts to the CKP terminal, but no spark I suspect from the immobilizer, the green key light flashes 4 times after I pull the key. I don't have the red key from the owner, so what would be the best method of getting around it?

 

bring it to the dealer and have them reprogram the immobilizer for $600, then buy another red key for a few hundred more.
never buy an immobilized ecu without the red key.

P.S. I replied to your other post. I doubt the original ecu is bad.