Sub not moving in a Lexus

Hi,
I have installed a Alpine CVA-1000 with a Ma Audio 800 Watt max amp with a 12" JL W3v2 in the trunk. I did that about 2 weeks ago and now he wanted a CD Changer, so I put in a 6 disc Alpine and after I got done and turned it on everything is working fine except the sub.... It is barely moving at all u can feel that the bass is moving it VERY little not even noticeable but nothing. The amp is turned on and shows to be working fine. I ran a new set or RCA's to the trunk and nothing, I checked connections on sub and they are fine. I checked with a OHM meter and I am getting 4 ohm what I am aspose to be. (The amp was getting really hot but no blown fuses anywher) So I finally went and hooked up a old Rockford sub I had and same ting..... Then I got out a Orion amp I had layin around and still nothin except barely anything. The fuse blew on this Orion after a bit. so I ran a "jumper" to see if it heated up and it was fine for about 5 min. then all of a sudden got REALLY hot...... The only thing I can think of is that my positive in getting grounded??? I have NOOOOO idea what else it could be!! He has not had problems with it since the 1st time I installed it. PLEASE HELP ME!!!

Re-ground the amp, check all the x-over settings, you may have bumped into a switch or something silly.  Also, try running rca's from a different deck.    Try the amp in a diferent car if nothing changes.   Eliminate 1 thing at a time.

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2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.

It definitely sounds like a bad ground. Try grounding directly to the chassis of the vehicle (drill a hole probobly, but be careful, check if there is anything below where you are drilling) and scrape away anypaint if there is any.