1993 Nissan Other

Engine Mechanical problem
1993 Other Nissan Models 4 cyl Front Wheel Drive Automatic 80000 miles

My Nissan NX1600 1.6L I4 has a steady miss in the second cylinder. I replaced the spark plugs and check the plug wires and the plugs themselves, it sparks. A mechanic said it could either be a vaccum leak or a bad fuel injector. My question is how can I determine which. I disconnected the plug and its wiring and started the engine. The air that blew out of the spark plug's hole smelt of gas, does this mean the injector works? What would cause loss of compression in just one cylinder? What can I do to troubleshoot this?
October 6, 2008.

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