The plug cannot be discarded as the cause of the problem.  The spark you
get when the plug is at atmospheric pressure is not the same as when the
plug is at 150 psi.  The higher the pressure, the easier for the plug to
fail/foul.

How do the plugs look? Dark, oily, dry, white?

Measure the cylinder compression.

Good luck

Just looking for advise to make sure I am on the right track. I have 91
sentra e 1.6 with 225,000 miles. Great car but everynow and then, I
loose a cylinder. For the longest I was thinking I was having
distributer troubles or a bad plug wire, but tonight the dead cylinder
came up again. I pulled the from the offending cylinder and tested
grounded against the engine, got a really strong spark. That to me
rules out the distributer, plugwire, and plug. Next, I took a
voltometer to the fuel injection socket and got a 13.86v good current.
I then tried touching a screwdriver to the top of the injector and did
hear the clicking but it did sound different that the first and fourth
cylinder yet louder than the second (odd, the second is firing right
now) .I am thinking with the extremely high milage that the injectors
are really clogged up and intermittently stop working. Am I on the
right track?