test drove my car after installing my turbo, and i had a couple problems, at boosting around 7psi i had a cel, checked it, it was a code 23, knock sensor, so first i found that one of my wires hooked to my mf2 was connected improperly, but my other concern was, my car has been sitting for two months with the same gas, would that old gas cause or contribute to this cel lighting up? i know that the main problem was that there was a problem with the mf2, but before i take it out again, should i empty the gas and put new gas? it just seems like a pain in the azz to do, cus i have to take off the plastic cover covering the gas tank right? or is there a drain plug that i can get to w/out taking off the plastic piece?
sorry for the long and drawn out question, but i just wanted to ask you guys for some assistance.

Thanks guys