Isuzu Repair: 1998 Amigo 4x4 starts/wont start/starts, ford quality, engine harness

Question
My wife's 1998 Amigo (4 cy., 4 wheel drive) sometimes won't start.  We thought it was the battery.  We had a new one put in, and the car started fine for about a week.  For the last month, it would start for a week, then not start for a day or two, then start fine for a week or so, before deciding not to start for a day.  As I said, this cycle has went on for about a month.  When the car starts, it runs fine.  

Today, it wouldn't start again.  It turns over and tries to start, but acts as if it isn't getting enough fuel to actually fire the engine.  We're thinking the fuel pump, but  since the car runs fine when it starts, we're hoping it just needs a fuel filter.  

Any thoughts?

Answer
Well I would definately have your starting and charging system checked. Also your main wiring engine harness ground as well ok? I would also advise a voltage check on your fuel system as well. It sounds as if your fuel pump solenoid brushes could be going bad. Mine did and it was doing the exact same thing. I just hit on the bottom of the fuel tank really hard alot of times and It would energize. SO that told me I needed to replace it. They call it the Ford Quality test. If you hit it or wiggle it and it starts to work? it is bad.