I have a 1995 Nissan Maxima SE that started having problems starting
recently.  When turning the key in the ignition, it would turn over
several times before finally starting.  Then the engine light came on,
and about a week later, the car won't start at all.  I pulled the codes
from the ECU, and it came back crankshaft position sensor (Reference)
and knock sensor.  I replaced the crankshaft sensor, but that didn't
help at all.  A mechanic friend of mine was over and looked at it
briefly.  He checked the spark, which was intermittent and not regular
like it should be.  Does anyone have any ideas?  Should I replace the
knock sensor?

Thanks!

Eric