Strange reception

Ok I wouldnt say im a newbie to car audio, but im by no means a veteran or an expert. Heres my issue, I am getting relatively poor FM reception and by that I mean i can get stations from my city pretty clear, but i cant pick up stations that i should easily be able to, if that makes sense. I took out the radio (pioneer deh-p6400) to make sure the antenna was plugged in and the ground was connected properly, the antenna was connected and so was the ground, well i figured I would "fool" around with the ground a bit to see if i could get better reception, so i disconnected the ground from the stereo to the wiring harness, and when I was touching the wiring harness wire end the reception was crystal clear, but when I connected it to the stereo it got muddy again.. What should I do?

Check to see that the radio's ground wire is going to a good ground source. You must use a meter to check it. Visual inspection means nothing. If it is good then check the antenna's ground with the meter. The outer connector on the antenna lead should show a perfect ground. The antenna will ground where it mounts to the body. Next check for perfect continuity from the antenna's lead tip at the radio (center conductor) to the antenna's mast. You should get a reading of less than 1/2 ohm. Lastly, check that the center and outer (ground) conductors of the antenna to insure that they aren't shorted out. A quick method for checking for antenna faults is to try the radio on the AM band with the engine running. If you get no or noisy reception, this usually indicates an antenna problem. sparky