I have a pioneer P860MP HU, and sometimes the signal fades constantly, also when I go through a tunnel it kills the signal completly, I never had this problem with the stock HU(non bose), is there some type of adjustment that I can make to the Pioneer HU to get a stronger signal?

 

Could be that the antenna power wire was not used when the Pioneer head unit was installed. Been so long since I installed my headunit I can't remember exactly which one it is (blue or Blue/wht??). Do a forum search on FM reception and you are bound to get a bunch of posts with the solution.

 

Thanks!