Hello all. Hope someone out there can help me with this. I got a 94 Impreza with a bad engine from my nephew. Bought a used one from a wrecking yard with 101,000 miles to replace it. All went well with the swap until I tried to plug in the two big terminals at the back of the engine. One of the terminals on the new engine had a different shape to it, making it impossible to plug in. I removed the wiring harness from the old engine and carefully replaced it on the new engine. Every plug seemed to fit fine with no "leftovers". I assumed the new engine was a different year or possibly from a car with a manual trans or something. Any way, I have spark at the plugs and fuel where the hose leaves the filter, but it won't start. I tried a little starting fluid in the intake and it backfires, almost as if the timing is off, but I understand that the timing is controlled by the computer. I have swapped the cam position sensor, the crank position sensor and the coil pack from the old engine. Any help would be appreciated.
I'd pull the left timing covers and verify cam timing.
You should never backfire out the intake. For that to happen, the intake valve needs to be open, either duing the compression stroke or right when the plug fires.
Are you CERTAIN that the ignition timing is right? IE, the right port on the coil goes to the right plug? You might try swapping the coil from the dead engine in case there was some other difference in the coil wiring.