Engine Light Won't Go Out

I have a 1997 Buick LeSabre Custom that I bought a couple of months ago. A new engine was installed on it shortly afterwards, and it was running fine up until a couple of days ago. It started knocking and cutting off whenever I would crank it up, and the only light that won't go out is the Check Engine light. I bought new plugs and had them put on, and it's still doing the same thing. What could possibly be wrong with my car? Please help!

Can you take it in and have the codes read for the "check Engine light"?This may help in finding the problem. Autozone, OReilly, or other autoparts stores can do this for not charge. It may turn out to be something that would not have required a plug change. That would be the first step. Good luck.

Thanks, I will go and have that done TODAY! As for the plugs, those were just changed yesterday, so that's not the problem either. But thanks for your advice!

A new engine or a Used new engine?