Grounding Issue

Okay, so I have been trying to install a Kicker ZX 350.4 in my ep3 for about a month now. There is an issue with the power to it, when i turn the stereo up past say 30 it cuts off (with the amps gain at about 1/4). The problem seems to be in the ground because i had 8 gauge wire in it and when i put 2 gauge wire on the ground you could turn it up louder (aka more power flow) This HAS to be a grounding issue, because I hooked up a 12volt power supply to the amp and it worked perfectly with the volume up to 50. I have tried the ground on the back of the back seat, the one attached to the shock, the one under the passengers side seat belt bolt, and then one in the side of the car that seemed to run the whole length of the car. All of this was done with 2 gauge wire and the problem still persists. Are the grounds in this car just really bad? I also tried putting another wire on the negative terminal to the battery to see if that was it. Still nothing. Help anyone.

Stop using existing grounds and make your own. See how that works.

Are you using the same size power wire as the ground wire? It sounds like it could also be a power issue. If i am reading the amp model correctly it is 350rms amp. On my ep i used the child seat bolt as my ground for my 4 channel amp and mono amp.

i had a similar problem with a 4gauge wire.... it would cut off after a certain volume.... upgraded to 0gauge and never had the problem again

The power wire is fine, my friend has the exact same rockford fosgate power wire and the exact same kicker amp (weird huh) in his Audi. I did try drilling my own ground on the little panel just above the shock and that still didn't work. An amp of such low power shouldn't need 0 gauge though, 8 gauge is enough 4 gauge is fine and 2 gauge is overkill for such little power.

im running almost 800 watts between two amps and dont have a problem, upgrade the factory battrey ground, im running my amp ground to the hole where the child seat rings in the trunk are,