94 TransSport Starting Problem

I have a 1994 Pontiac TransSport and for the last several months have been having a problem with it firing up. It will turn over and crank and crank, but won't fire up and inadvertently for no apparent reason it will just turn on. Sometimes I will be driving along and it will completely shut down in the middle of the road. Other times I will go out to the store, go in the store and come back and it won't start. When this happens I try to start it and randomly it comes back on. We have had a tune up done, replacing the spark plugs, an electronic diagnostic and an engine diagnostic which came up with nothing wrong. The car will start 100 times and then randomly not start. It worked great for a whole week and then didn't want to start again. I cannot seem to find a common denominator with all of this. Can someone please help?

Most probable cause: crank position sensor, a common problem. Looks like a similar case in that forum recently...will try to track it down....ah yeah, was a bonneville...same engine..(3800)

What follows is for 3800.
First thing you should do is read error codes.:
Reading the codes with OBD1 is simple:
Locate the diagnostic plug under the dashboard
www.avigex.ca/xport/plug.jpg
jump connectors a to B with a paperclip or small wire
turn key on
the check engine light will flash code 12 - one then 2 short flashes, repeats 3 times, (this indicates the computer is in diagnostic mode) and then any stored code will come, like 34 is 3 flashes then 4 and each code is repeated a few times (have paper and pencil handy) then when finished it repeats code 12 and goes around again.
COdes are here:
www.avigex.ca/xport/3800codes.jpg

If you have a code 18 or 42, this will confirm the crank position sensor diagnostic and then you might need this:
www.avigex.ca/xport/positionsensors.jpg
www.avigex.ca/xport/ckps.jpg
www.avigex.ca/xport/ckpsremoval.jpg

the other common problem is a fuel pump going bad. when an electric fuel pump starts to go bad, it will develop a dead spot on the armature. The only time it doesn't start is when it happens to stop on the bad spot. After trying several times, the armature will move just enough to clear the bad spot and the pump will take off and the vehicle will start. The next time your van doesn't start, check to see if you can hear the fuel pump running when you turn the key on ( it should cylce for about 3 seconds then shut off) by taking the fuel cap off and listening while someone turns the key on. If you hear the pump, then I agree that the crank position sensor is the culprit, if you don't it's the fuel pump.

Thank you for your replies. The family has had the flu all week and we haven't had a chance to check anything out, but hopefully this weekend we will get a chance to check both replies and will keep you updated.

Again thank you very much.