Wrangler starts, runs for 3 seconds?

I've got a 2000 4-cylinder manual Wrangler. The other day, after
stopping for a bit in the back-country of Big Bend National Park, we
started experiencing a problem. The Jeep would start and run normally
for roughly 3 seconds, then quit as if the ignition were turned off. I
checked everything I could at the time, including fuses, relays, fuel
delivery, and airflow. Fuel was near full and oil pressure read normal
before the engine cut off. Problem is reliably repeatable (meaning I
still can't get the blasted thing to run for more than 3 seconds).
Couldn't find anything obviously wrong, which makes me suspect it's an
"electronic" problem. Does anybody have any ideas what to look for?

After waiting for about 8 hours, the Border Patrol finally found us and
dispatched a *very* expensive tow truck to haul us back to our RV. With
the Jeep malfunctioning, we cut our little vacation short, hooked it up
to the RV and drove home. I'm reluctant to take the Jeep off-road again
until (1) I know what caused the problem and (2) have a way to fix it
(at least temporarily) in the field should it happen again.

Thanks for your help,
Bill