My husband replaced the 4.6L V8 engine and transmission in my '95 Cougar with another 4.6L V8 engine (with approx 46,000 miles) and transmission out of wrecked '95 Cougar. I know he replaced wires, plugs, and power pack. After all was back together he drove it and the check engine light came on. Had it checked to see what the code was.....P0402. After researching that code, we found several things regarding the EGR could be faulty. He first replaced the DPFE sensor, unhooked the battery to reset computer. I drove car to store (no light came on), after starting car to go home the light came back on. Had code checked again, still P0402. He then replaced the EGR valve (what a job that was for him), unhooked battery to reset computer. He drove car to town (no check engine light on) and when he started car to come home, light came on again. He stopped at a different auto parts store and had code checked and was told it was the PCV valve (didn't tell him the code). He then replaced the PCV valve. He also decided to change the computer thinking it might be the problem (the computer that was in the car was the computer with the original engine and he kept the computer that came with the engine from the wrecked Cougar). He started the car this morning to take it from his shop to the driveway (no check engine light came on). When I got in it and started it the check engine light came on. I will be stopping again on my way home to have the code checked. In the meantime, I am hoping someone has some suggestions of what the problem might be and what needs to be checked or replaced. Thank you for any help or suggestions!