Ok so I have a 93 civic CX hatch that came with a D15, the engine and tranny had seen better days, so I swapped it for a D16Y7 SOHC non-Vtec. I swapped over the D15 intake and exhaust manifolds, as well as the coolant tube to the D16. I still have the CX ECU from the D15 as well. When I installed the new engine there was 1 plug that i couldn't find a home for. Its by the timing cover and i assumed that it was a crank sensor. Guessing that my 93CX ECU wasn't going to look for something that wasn't in a CX from factory I left it unplugged. The car ran fine, although very rich, since December. Now today, on the drive to work, it throws a CEL and sputtered until the light stayed on continuously. When I got to work I checked the code... 9 CYP sensor! Is my ECU checking for this even though it wasn't there from factory? Do I have to wire in this sensor? Or do I have to buy a new ECU or engine wiring harness? Any help would be much appreciated.

Thanx Geoff