minivan V6 intermittent start problem

Hi - posting for a friend.
He has a 1999 minivan with V6 having problems starting.
Most of the time it is fine, then all of a sudden, it will crank but not
catch.
He has towed it to the dealer 2 times, but by the time they look at it, it
starts so they cannot recreate or diagnose the problem.
Does anyone have more insight into this problem?
One thing I am thinking is the crank or cam position sensor going bad? Is
this a possibility?
His wife (its her vehicle) won't use it any more because she doesn't want to
get stranded.
Thanks in advance for any help.

 

I have a 1993 Grand Voyager with intermittent starting also. We have
narrowed down the issue to the fuel pump. You can hear the "whin" of the
pump before starting. If it doesn't "whin" it won't start. Our mechanic
replaced the fuel pump module and we had no problems for over a week. Then
it hit again. Mechanic had it for over a week but it started for him.
Today, it started it's "no start" problem after we got it back from the
mechanic. Mechanic said it could be something in the ignition or a relay.
This problem has been a issue throughout the year, more prevelant within
the last few weeks. Will post soemthing if we find the exact problem.