How do you know if the fuel pump bad?

Answer 1

The fuel pressure and output volumes must be tested to begin with, as should electrical voltage at or near the pump (electric ones). Most preferably at the moment that you seem to be experiencing a problem; easier said than done in some cases.

When trying to diagnose intermittent fuel pump problems, your best and easiest option is to visit your favourite mechanic, again, preferably at a moment when you are experiencing the problem. Trust me, most mechanics will drop what they are doing for a moment to try and get a handle on an intermittent problem now, rather than wait for the problem to occur on a test drive later. The mechanic will probably install a temporary fuel pressure gauge, and possibly a flow meter, that can be read by either you or them while driving, and, more importantly, while a problem is being experienced.