Hello everyone,

About 3 months ago my 95 engine died (3 cylinders no compression). So I decided to put a used engine in it b/c I love the car so much. The used engine is from a 98 vehicle with only 20k. I haven't driven the car that regularly b/c I was vacationing for a while. Prior to vacation the car drove fine, but when I got back the car has been starting horribly and it keeps dropping the (0407) Crankshaft Position (REF) code and the (0101)upstream left bank oxygen sensor fault. Maybe there was a problem since the engine swap and the ECU had to collect the data, so the problem didn't show up until afterwards. I have been to 2 different shops including the dealership. The car has also backfired on a few starts.
So far the grounds have been checked, the ECU has been opened and inspected, the wiring harnesses have been inspected. The timing and firing of the plugs have been checked. Still cannot determine the problem. It's quite frustrating to have a near new engine put in with problems like this.
Any ideas ? Incompatibility between engine and ECU ? Any mod's that needed to be done to the sensors or electronics on the engine so that it can run okay in a 95 ?
I'm really at a loss here, any help is much appreciated. Sorry for the length, trying to give all the info.