Cranks but does not start (sometimes)
My 1993, 4cyl, Ranger has failed to start a few times recently. The engine cranks over nicely, but there are no "almost starts" or coughs, it just cranks and cranks without starting. The first time, about two months back, it happened when I went to drive home from the store just a few miles away. After about 30 minutes and various guys trying to help out, it started but nobody knew why. I have been driving the truck every day since and it starts instantly several times a day. But there have been five or six repeats of "not starting". Sometimes it doesn't start after siting overnight and sometimes after having just driven somewhere. It can be 30 minutes or a couple of days before it starts again.
I replaced the spark plugs and had some "electronic box" (about 3x5 in) checked out by the local NAPA store. They said it checked fine. Any ideas?
1993 Ford Ranger XLT, Extended cab, 4 cyl