Engine Mechanical problem
1990 Volvo 740 4 cyl Two Wheel Drive Automatic

I put an engine in a '90 740 wagon from another '90 740 wagon. We drove both cars into the shop. I'm getting gas and strong spark, but it just won't start. I replaced all relays and fuses, the cap, rotor, plugs, and wires, injectors, injector rack, and sensors. It kicks back on the starter, but only on one cylinder. I checked the alignment on the timing belt 4 different times. I tried starting fluid, but the same same result. What could it possibly be??