How to know if timing belt has broken -sans pulling cover?

Engine 2Lt seem fuel starved. I was thinking could be timing belt broke. Thought banding a plastic trash bag to tail pipe and observing its undulating when starter cranked engine solidified that the belt was in place and valves were opening in timed fashion but am having second thought about this logic. Any Ideas for a quick check would be helpful. Thanks RWP

On the chance that there is another seeking the answer to my own posted question I believe I have found the answer - at least for a 1990 2L t .
If you move the top radiator hose out of its support harness you will discover a stealth rubber plug in the timing belt cover at the location of the overhead cam pully bolt. crank the engine to discover if it moves. Same is true for the water pump pully.