furnace blows hot air for about 3-4 min. (burners all firing nicely) then burners go out but air continues to blow (cold) for 3-4 min. All registers are open and the pressure is VERY strong (small house - 6 ports) cycle repeats about every 10 min. or so. Also, what would the black plastic bucket full of water (20gal. or so and half full) and connected to furnace be? appreciate any info. thanks

Does this furnace vent outside with PVC pipe?

Drain the bucket, it's the poorman's way to catch condensation from the furnace. The correct way is to install either a gravity drain or a condensate pump to rid the furnace area of this acidic water. This may solve your issue. If not clean the flame rod or sensor with a stiff brush or steel wool. The sensor looks like a rod and is usually found next to or in front of the burner. Do not mistake the igniter as the flame rod. The igniter will have two wires going to it and may be very brittle even to the touch. Prior to doing this, cycle the system and note which component glows orange prior to lighting. This will be the igniter.

The water is a byproduct of combustion. Your system is a high efficiency unit and instead of a lot of water vapor being expelled from the vent, it is being displaced as water. This is a good thing and yo are probably getting 90% or more efficiency out of it.

furnace blows hot air for about 3-4 min. (burners all firing nicely) then burners go out but air continues to blow (cold) for 3-4 min. All registers are open and the pressure is VERY strong (small house - 6 ports) cycle repeats about every 10 min. or so. Also, what would the black plastic bucket full of water (20gal. or so and half full) and connected to furnace be? appreciate any info. thanks
Yeah HVAC1000 - its vented outside with 2 seperate 3" white pvc pipes. therinnaiguy-As far as the bucket goes, cant drain it cause it seems to be plumbed into the furnace (theres no drain located on it) Looks to have a pump inside it though just no where to pump the water into. I'll try draining/pumping and cleaning the flame rod. Many thanks

I asked about the PVC pipe to see if it was a high efficiency furnace. Check and if necessary replace the pump or find a a way to drain the furnace. it is a bit hard to believe someone would have used a bucket system but If there is no drain I guess it is just like using a condensation pump for A/C.