My Blazer is hard to start only when the engine is warm, when the engine is cold it starts fine. From about 10 min. after I shut the engine off, to about 4 or 5 hours later is when it has trouble starting. In this time period it takes about 3 to 5 sec. of cranking to start (a little less when hold down the gas pedal). When the engine is cold it takes a fraction of a second of cranking to start. This problem started slowly, and it's now been happening for more than a year. I thought this could be a problem with the intake air temp sensor or the engine coolant temp sensor, but I checked them and they are both working correctly. I hear the fuel pump turn on for 2 sec. when I turn the key to on, and I tried cyceling the key from off to on about 4 times before starting and the problem still happens.

I don't know if this is part of my problem, but about a month ago I started getting "random misfire" codes. I have replaced cap, rotor, plugs and wires, and I am still randomly getting this code. I don't know if these problems are related, but I figured more information is better than less.
I found another thread with the same problem, but it was never resolved. Here is the link http://www.automotiveforums.com/vbulletin/t395805.html

I would apprecieate any insight from anyone, I can't wrap my head around this problem.

1997 Chevy Blazer LS
4 Door, 4WD
4.3L CSEFI, Engine code W

What year and what engine?
If you are getting misfire codes you need to keep working on that end.
Does the scanner pinpoint what cylinder is misfiring?
But I would also run a good fuel pressure check on it.
Hook a gauge to outside of mirror or windshield and watch fuel pressure when running and when you shut it off and try to restart.
Post back fuel pressure readings and watch for a fast leak down when shut down.

Just a question MT, the spider injector fuel pressure regulator senses and regulates by the pressure inside the intake, could it be going bad and not properly regulating the pressure while it's warm? Bad pressure regulator could also cause the random missfire, couldn't it? I think if I had to "throw a dart", I might try the regulator. About $70 when I bought one a few years ago. Good time to inspect the injector hoses as well.

Just a question MT, the spider injector fuel pressure regulator senses and regulates by the pressure inside the intake, could it be going bad and not properly regulating the pressure while it's warm? Bad pressure regulator could also cause the random missfire, couldn't it? I think if I had to "throw a dart", I might try the regulator. About $70 when I bought one a few years ago. Good time to inspect the injector hoses as well.

The fuel pressure regulator controls fuel pressure but the fuel pump has to have good pressure for the regulator to control.
Around 75/85 lbs of full pressure at fuel pump
You need to run a fuel pressure test to see what direction to go.

Hard to start.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak.
Post back fuel pressure readings.

I gave my engine information in the first post it is a 97 Blazer LS, 4 Door, 4WD, 4.3L CSEFI, engine code W. The code they got on the scanner is P0300 - Random/Multiple Cylinder Misfire Detected, this turns on my service engine soon light for a few days, then it will go off for about a week, then it will come back. I am going to get my fuel pressure checked this week hopefully.

Also just to let you know I brought my car to a repair shop 2 yrs. ago and he said my injectors were leaking, and told me I would need a whole new rail (cost me $600, I wish I knew about the switch to MFI back then). The thing is I never had a starting problem before then, the starting problem happened about 6 months after that repair. I will post my fuel pressure readings when I can get them. Thanks for everyone's help so far.

Random misfire codes can be misleading.
Can be caused by a lot of things.
Here is a good one.
http://www.automotiveforums.com/vbulletin/forumdisplay.php?f=589

If it is setting misfire codes you need to get it n a good engine capable scanner that will read out what cylinder is misfiring and how many times it is misfiring.
Also all other data that can cause a misfire.
Besides secondary ign problems Low fuel pressure and MAF sensor off is some leading causes of random misfires and camshaft retard setting off to and dirty injectors.
MT

How many miles do you have on it? I fought with a random missfire for a few years through plug changes, EGR valves, wire, cap & rotor changes, fuel pressure regulator change, O2 sensor changes, coil replacements, etc. The only thing I've seen/read on this site that fixed it on high milage engines was a timing chain replacement which I finally did and another person that forced a distributor adjustment. My initial fuel pressure with key on was 61 psi. Engine running was 57. After the timing chain replacement, engine ran great with those fuel pressures. The timing chain I replaced didn't show much slack, but apparently didn't take much. For more info, do a search for "Intermittant miss at light loads". You'll see what some of us went through trying to chase down this "Gremlin" that seems to plague the Blazer.