I was told by the previous owner that my 96 gt car has PI heads and intake but i didn't believe him so when i bought plugs for the car i bought them for a 96gt, the plugs had only half the threads compared to the ones i pulled out of the car so i swapped them for a set for a 2001 gt which matched the threads(but had a smaller gap). when i took it down the road after the plug change it started missing so i pullover and popped the hood to find that three or four of the spark plug wires had popped off the plugs at least an inch so i was only running on half my cylinders...i stuck them back on and drove it and the same thing happened again. Im sure the wires are tight and i tightened all the plugs pretty tight. What could be causing this?, i figure its not sealed at the plugs or something....i think my intake is npi(it looks shallow and coolent hose hasn't been relocated), but the pi plugs match the plugs i took out of the car??? whats going on here? could i have a npi intake on pi heads or do i have npi heads and just had weird spark plugs in them?