I have a 2008 Tahoe Q4 3.0L 4cyl (135hp) bow rider and would like to adjust the ignition timing. I've done research online however the 2 white wires going to the distributor which are suppose to be jumpered to bring the engine to base timing, do not exist. the colors that I have at the distributor are white, black with white stripe ,purple. Does anyone have any idea which 2 of the 3 i need to jumper before adjusting the timing?