Audio Systems: Subwoofer Problems...., dual voice coil, pioneer subs

Question
I have a 4000 watt pile driver amplifier and 2 12 inch dual voice coil pioneer subs(1000 watt rating)and a 1.5 farad cap. For some reason i can't get both subs to hit with equal force its either one or the other.... I don't think it's a power issue but I'm not the expert. When one speaker is hitting fully the opposite will barely flex. Any idea why?

Answer
Interesting problem...

I'm happy to help if I can, but I'll need a few answers first:
-Are both subs in the same cabinet (i.e. not seperated from each-other?)
-How are the coils wired?  Is each sub on a seperate channel?
-Is it always the same sub that seems less forcefull?  Does is switch randomnly, or after you swap wiring or otherwise tinker with it?
-Where is the sub cabinet in the car?  Is it assymetrical in any way, or placed off center in the car?
-How do you know that the speakers aren't equal?  By sight (looking at excursion)?
-Where is the crossover for the sub?