Replaced factory radio with a pioneer unit. Radio reception very poor. Installed powered antenna adapter. No change. Any ideas?

One way or another, you have a poor connection from the radio to the antenna. Check the following and make sure all cables are clean and completely and properly inserted:
- a poor antenna cable connection to the adapter or from the adapter to the radio
- a faulty adapter
- a damaged antenna cable connector (wire in center pin)
- a damaged socket on the radio

check and see some radios need a extra ground not just to the frame of the radio. and some antennas have different size plugs make sure it is tight and making contact both places the little one in the middle and the bigger outer one.

Dealer should have recommended replacing the entire unit. There is a fault in it. Changing the antenna is not going to help.

check your antenna wire to see if it came unplugged from back of radio

Sounds like the dealer may be correct to me, but make them guarantee the job.

you can try a AM/FM antenna booster if you know how to get to the back of the radio. Otherwise the radio ground needs to be checked out and the antenna ground would need to be tested to see if there was corrosion on the antenna base or the connector to the back of the radio. On some cars the antenna is located in bad area and they don't get the signal boost off of the cars ground plane The more reflective surface you have on the car the more radio waves will bounce back and increase signal strength. Also Depending on atmospheric conditions and skip conditions sun spots and other natural occurring things can cause poor reception. The signal booster is about $10.00 at any radio Shack or any auto parts store. Hope this helps.

It should- that splitter is generally used for factory telephone reception and also there is an antenna located in the rear window glass. It will work for radio reception but it will interfer with your phone if you have a phone installed. just make sure you have a good antenna ground. Try removing the grond and sanding the metal so that there is no paint or oxidation that causes higher resistance. This generally affects a.m. reception.

could be or the station you have on.in between towers you will get static.

i have a 1990 iroc-z and i replaced the radio with an aftermarket radio. when i replaced the factory radio i had to do a little manuvering of the wires because of the alarm i had installed. the antenna wire is supposed to be ran under the PASSENGER side i dont understand why they are under the driver side.

I would suggest installing what is called a filter capacitor.You can get these at most car audio shops or a electrolytic capacitor rated at 16v or higher and around 30uf (the capacity is not very important) you connect it from the Positive to the Negative on the radio. The idea being a capacitor will allow the A/C current (noise) to pass through to ground without going into the radio and this is usually the cause of poor reception.

Another possible cause could be simple a poor quality antenna, some manufacturers are going cheap on the antennas since most people don't listen to the radio anymore. You could try to screw an antenna off of a different car onto the base on this one and see if that clears up the problem, they are a some-what universal thread.