timing question

[gmcturbo]

i hooked up a timing light today with the tan wire disconnected and set it to 0. with the tan wire disconnected when i rev the engine should the timing change at all? it was moving like 6 deg. and reving up and down sounding like it was gonna die. this ty is driving me crazy!

 

[jwaller]

it's normal. I've seen this on several trucks.

 

[ItsMyTy]

did you verify the TDC mark with a piston stop? mine was spun on the damper about 10 deg.