My gas pac keeps cycling on and off. I cleaned the flame sensor and that did not solve the problem. After about four tries it will shut down completely. Burners look OK. If I remove the access door it will burn like its suppose to but once I put the door back on it starts to cycle again

Take the cover off the burner compartment of the furnace. Obtain the make and model of the furnace off the rating plate in the burner compartment and post it here.

Observe the sequence of events that occurs at the furnace when you turn up the thermostat and post that sequence of events in order and in detail.

It works with which door removed, the combustion door, or the blower door? Ive got a couple thoughts, but need more info, specifically the info SP asked for.

Sounds like you have a limit switch that is opening due to lack of air flow. Count the blinks of the lights on the control board. The code should be located on the blower door telling you what the fault is.