Intermittent "Service Engine Soon" light

I'm new here, so bear with me. I'm having a problem similar to others I've seen in the forums, but haven't found the same circumstances I've been experiencing. 1998 Blazer, 4WD, 4.3L, about 110,000 miles.....This has happened to me 3 times now. The 'SERVICE ENGINE SOON' light is on, (when I turn the key on) no other electrical problems obvious. I can't hear the fuel pump kick on. After 2 or 3 days I can go out and it will start right up, no 'SERVICE ENGINE SOON' light any more, and I can hear the fuel pump kick in. It does just fine for about 3 or 4 weeks, then does the exact same thing again. I am clueless. Help anybody?

When key is on engine off it is normal for service engine light to be on.
Does dash light up normal and does the security light go out after bulb check?
First check for lose of spark to 2 or more spark plugs.
If good spark find the fuel pump prime wire or gray 12 volt feed to fuel pump and check for 12 volts on it with key on 30 second prime or engine crank.
Any add on anti theft or remote starts?

Yes, the dash lights up normally, and the security light goes out after bulb check.Negative on the anti-theft or the remote start.
This morning I turned the key, and heard the fuel pump kick in. The sucker started right up. It runs like a top after I do get it started (so I think that all cylinders are getting spark). I just don't get why the fuel pump just up and quits, and then "magically" starts working again. From everything else I've read, it seems imperative that everything stays 'sealed', as the system is pressurized at all times. With that being said, could it be possible that the gas tank cap is faulty? Doesn't the 'SERVICE ENGINE SOON' light most generally have to do with emission controls? And would a faulty gas tank cap cause the fuel pump to not work?

Gas cap or tank seal up has nothing to do with fuel pump running or pressure.
First check is for spark good hot blue spark to all plugs on a no start.
If good spark check for fuel pressure and 12 volts to fuel pump gray feed or prime wire on 30 second prime or engine crank.