1994 Lumina 3.1 intake backfire

i have a 94 base model lumina with the 3.1 liter in it and yesterday it started backfiring thru the intake i know this because you can hear it resonating in the tube it self. it started doing this only when the gas was floored real quick and now it is backfiring when any load is applied to the engine. ive already thought about either a lifter or timing but i ruled out the timing because the backfire is only on one cylinder. any other ideas im open to anything before i go diving into this damn motor to rebuild the top end

check for a stuck valve/lifters, got any clicking?

no tapping clicking or anything thats what is so damn weird about this to me especially with the backfire happening on one cylinder

In the dark torque it up in gear and see if you see any spark exchange across plug wires.

A vacuum gauge reading will tell you if it's a mechanical problem like a stuck intake valve or broken valve spring....handy tool for $25....

well dug into the car today pulled upper intake manifold noticed one black oily runner and one completly dry runner so aparently had a injector not firing on number 6 and number 3 has developed a horrible tapping so im goin with a bad retainer or a broken spring compression is down to 50 on cylinder 3 which was the one with the oily carbon covered runner