Need help please identifying the engine we are working on. It's a 1991 honda Civic 3 door 1500 car, but we have a suspicion the engine has been switched out. (We just bought it.) The engine number is A18150570. Do you know how to find out what year this engine is?

You'll need the block code. Look where the engine and transmission meet. On the exhaust side of the block on the driver's side (on your right when looking at the block) there is a small square with the engine code and serial engraved. Should be like D15B7, D16Y8, etc. What is the code? It may be impossible to determine the year but as long as you know the block code you can usually figure out the year range.