Backfire in the Intake???

[2kdet]

I have a NX2000 with a Det swap?The problem that I am having is that I am getting what to be a popping noise or backfire through my intake.And idling very rough.I have changed the sparks plugs and Cap and rotor.I pulled the #3 plug and it is Dry fouled.which looks sooty.But the others are normal.I swaped plugs and the same thing.I check for spark,and there is spark to the plug.And I checked the fuel injector on number 3 plug and it is working fine.I check for leaks through the o-rings they are fine.I even swaped out injectors with the other injectors and I still get the same problem.I could drive the car normally.But as soon as I get on it,I get the popping noise with sounds like backfire through the intake.And really bad hesistation.I have checked for compression and it checked out fine.I really think that the cylinder is not working.Because when I pulled that plug while the car was at idle,there was no change in engine speed.Just running rough.Please help me.

[sentra2nr04]

hmm check the timing

[2kdet]

The timing is ok.

[RED_DET]

Exhaust valves probably the culprit. I see some head work in the future.