This may or may not be similar, but the four cylinder engines in Ford Escorts had a nasty problem that started with #4 cylinder misfiring. Eventually the valve seat would drop out of the head and into the combustion chamber that that was all there was. The problem started with overheating. Check the spark plugs and look for signs that the cylinder is running hot. If caught early on the Escorts, a rebuilt head was the fix; far less expensive than an engine. Again, I don't know if the engine in your vehicle has this problem, but it is a Ford, it is #4 cylinder and it is misfiring. I suggest you take it to another repair shop; a new engine seems extreme.