I have a 2005 Honda Civic EX. The VTEC d17a2 blew up in it, and I found a donor '02 Civic with d17a1 non-vtec. I took out the a2 harness and all and swapped in the a1 with it's harness. I swapped the ECU from the '02 a1 into the '05 car and it wouldn't fire at all. Turns over with no spark. After checking all my connections I swapped it back out with the '05 a2 ECU and it fired right up, runs and drives good but goes in to limp mode around 4k RPMs, I'm guessing bc it is trying to kick VTEC in but it ain't there? What are my options to get it going right? I'm guessing an '05 non-vtec ECU? Thanks for the help in advanced.

 

Its because the immobilizer isn't permitting you to start the vehicle. You need to get the A1 ECU paired with the keys/immobilizer ring, for the engine to fire.