How do I replace the crankshaft position sensor on my 98 discovery?

 

Download the RAVE in my signature. It will answer 99% of your questions.

 

What is wrong with yours?
here is a picture of one for your truck.

 

Well it dies when it idles, and I went to crank it last night, it turns over, batterys fine, spark plugs, wires, and timing chains are fine. But won't crank.

 

You have too many fines there. How do you know all those are fine, what is the charging system voltage, how did you check the change, although it has nothing to do with your problem.
When was the last time you replaced your fuel filter? Might want to start with a fuel pressure test.