1988 Pontiac Bonneville LE

I have a 1988 Pontiac Bonneville, that won’t stay on. Most of the time it cranks right up but soon dies out. I have replaced the battery, the starter, the fuel pump, fuel filter, and about nine months ago the mass air flow sensor. We’ve also had the alternator checked at Auto Zone and it’s still good. Any thoughts on what can be the problem?