my 2002 xj8 jaguar will crank but not start. we replaced the key and crank shaft sensor. Still it wonts start reliably

 

Does that mean that it will start occasionally? Do you have a CEL?

Here is the official 'won't start' check list.

https://www.jaguarforums.com/forum/g...d-first-30792/

I would add the additional thoughts that the starter is capable of rotating the engine at voltage levels below what the electronics will tolerate and have you checked the fuel pressure at the fuel rail. These are probably the two most common issues.

. . . and welcome to the forum!