1999 Grand Cherokee is now stopping g without warning. I let it rest then it starts again only to stop a few miles down the road. My mechanic could not diagnosis the problem because the car didn't not die on him when he tested it. he checked the obvious, alternator, fuel pump, and timing. with no conclusion I picked it up from the shop and it took me four, dead on the track, stops to get home.
Does anyone have any ideas of what is the root of the problem?

 

Get the OBD (on board diagnostic) system checked for tripped codes. Maybe your mechanic did already. If so give us the codes.

 

My guess? Failing crankshaft position sensor. It usually doesn't set a code.