QX4 won't start

[spherey]

Hi guys, newbie here.1997 Infiniti QX4. Almost 183k miles on it now. I've had the vehicle for over 5 1/2 years with very few problems.

When I start up, the engine cranks and cranks but will not turn over. This only seems to happen about every third time I want to start up. When it does happen, it takes about 15-30 minutes, but eventually, so far, it does start. I've replaced the fuel filter and the fuel pump, and at first, it started right up and did fine -- problem solved, I thought, but just like when the problem first came to light, yesterday I made about five stops, and although after each of the first four the car started right back up again, the last time, it did the same thing again.

Once it does start, it's good, though it sort of bucks and surges a little bit while I'm driving (very rarely). No smell of gasoline. No engine lights. I checked the wires and plugs twice, and they all still seem good. No gunk, everything clean, no sparks. I've looked online a bit further, and hear all kinds of things that sound potentially plausible, but they're all across the map -- oxygen sensor, PCM, catalytic converter, a secondary fuel filter that's apparently under the hood (my manual says the filter is under the hood, but the one I replaced was under the car near the tank), the coil, and the computer. Do any of those sound any more likely than any of the others? Do you have any insight about anything that's worth checking on my own that I haven't thought of, or is it time to pass the buck and take it into the shop?

[fueler]

hmm. have you hooked up a OBD2 scanner to see if there are any codes?

Sometimes there can be codes stored in the computers memory but they wont illuminate the check engine light....

[spherey]

I haven't yet. Is that the type of scanner that Autozone has? I read on here that they'd scan for codes at no charge . . .