96 Grand Marquis - cranks but won't start - continual problem. HELP! Any other ideas??

For over a year, I've had a problem with our 96 Grand Marquis turning over or cranking, but not starting. This seems to happen more often in the morning after it's been sitting overnight (or hasn't been driven
for a while) , but not always (and maybe when it's also damp out in the a.m. or cooler - but again, not always). We can no longer count on it being reliable because of this, but hate to get rid of it since it's paid off and holds our family comfortably. It seems like it should be simple to repair - fuel or spark - but no one can get to the bottom of this.
Rather than go into minute details, I will sum up the repairs: tune-up in late 2004 (plugs and wires replaced), IAC replaced spring 2005, new battery fall 2005, new fuel pump (tests showed failing) and fuel pump relay 2006. The usual things were tested, etc., etc.., fuel filter fine, etc... BUT, the problem goes on and on and on and...
In addition, when it won't start, it seems a battery boost or charge will get it going again - until it decides not to start once more. That can take anywhere from a few days to a few weeks. We did have a period of time last summer where it started for several months in row with no problems.
What are we missing? It seems to so obviously be a spark or related problem, but are missing something totally unrelated?
ANY ideas are appreciated! We have a soon-to-be teenage driver, and we REALLY hate to buy another car when we can't afford it and with the gas prices! BUT, I've had it with this car and am ready to give up. Wondering if anyone can give me some other suggestions? Neither I nor the 2 mechanics I've taken it to can seem to find the problem, and naturally it tends to start at the mechanics, of course. What are we all missing?
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On 23 Apr 2006 13:16:18 -0700, "friedpasta"

I recently had a head scratcher with my CV with an iffy fuel inertia switch. Found a good one in salvage yard for $10. You should also should have a diagnostic scan done.
Lugnut
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