Does changing the water pump cause the timimg to be off?

thank you so much, so what has to be done to fix it?

Who did the work and do they have (or access to) a service manual to see how to install the chain properly?

I will make sure that he looks at the service manual to install it properly, I don't have to purchase a new one do I?

any year manual that has the correct inf & diagrams , to install the chain &tensioner set-ups (that apply to an '01 QX4) should be okay.Otherwise , if you have a friendly neighborhood nissan or infiniti dealer around , they might be able to help some.Years ago when I had my own shop , before everyone was on-line I would routinely go in and borrow dealer manuals for job specs & special procedures (I also purchased a lot of parts from them). good luck.