Hi, I just installed an intertherm m3rl 90+ downflow furnace today and what happens is the inducer fan runs and is venting proplerly, but when the flame lights and blower fan is signaled, the blower is blowing out the flame. How can this be possible unless there is some sort of leak in heat exchanger. Please help me!!

Yep sounds like a bad heat exchanger or a real bad install. This sounds l;ke it is in a trailer/mobile home..
Did you follow these directions EXACTLY.

http://www.nordyne.com/Literature/708219e.pdf

http://www.nordyne.com/Literature/7103270.pdf

Exactly what you problem I have no idea I figured I would post some instructions.

Akso make sure you have plenty of combustion/makeup air.