Is it a 6 cylinder, or an 8 cylinder? If it's an 8, is a 4.6 or 5.4 liter.that's just for starters. You need to know what condition the rest of the truck is in but also, what configuration is it (Regular, Super Cab, etc) and what trim level is it (XL, XLS, XLT, Lariat, etc)? All this matters to give you an idea of what it would be worth if you fixed it. Also you need to know what is wrong with the engine to determine if it needs the engine replaced or repaired. Here in So California, a 2004 average about $6,000-7,000 in good condition with mileage between 120K-180K miles. Have the entire truck inspected if you want to buy it, so you know what is wrong with it. I'd see if a reputable mobile mechanic would be willing to do an inspection. \They cost about the same as (or less than in many cases) a shop mechanic, plus they come to you. . No overhead so you're just paying for fuel and their time.