upgraded eclipse problem

I couldnt tell you since im not there to look, but i think the knocking has to do with a cylinder heating up to hot, or slipping, or misfiring... You could try finding the cylinder thats having the problem and replace it, but there might be more to fix as well... so if you get it, I would rebuild the motor or replace, the choice is up to you .

It could be one of quite a few things, from something as simple as having a very high compression ratio/boost and the owner being stupid about low octane fuel to someone trying an insane intercooler delete setup on it. Or you get lucky and maybe its just that the fuel/air mixture isnt tuned right. Either way, its unlikely that you'd have to replace the ENTIRE motor. Maybe several parts that would cost more than the car is worth now, but probably not the whole thing. But still, I wouldn't take the risk. There's plenty of eclipses for sale out there, skip out on that one.