07 S8 not starting and driving us crazy....

Ok, we just changed the intake manifold, fuel filter, about a month ago the right side fuel pump, fuel control module, new battery…
Car ran great for about a week or two, then started stalling till finally no start…
Have tried everything that we can think of, so looking for fresh ideas here.
No codes, no lights, nothing???

My son has lost faith in this car and wants to go back to the S4 new style, so once we get her started, he may sell…

Still we are looking for fresh ideas to look at for this challenge, we did have the car flat bedded to a local shop but they are so busy it maybe a few days before they look at it.

Thanks for any help anyone can provide…