if you take the top of the plenum off, i bet the plastic fuel line inside has a crack in it. (the inlet outlet lines) i had the same problem where my truck would crank for like 10 seconds b4 starting, and would start fine for the rest of the day. if it sat for more than 5 or 6 hours, it would act up again.
i forget why i had the plenum off, but i remember turning the ignition on to test something and when i went back to under the hood, there was gas everywhere.
i hope this helps and i hope if it doesnt i hope you figure out the problem

 

6/29/2008(finally home from dealer after overa week)~ update (hopefully the last for awhile) ~ blazer is finally home from the dealer's shop.
they replaced the upper & lower intake gaskets & the fuel pump & did an oil change (probably because oil was contaminated from coolant?).
they found coolant in the number 3 & 5 cylinders & in the fuel pressure regulator when they were testing for the fuel pressure regulator & spider assembly. they didnt replace the fuel pressure regulator nor the spider assembly.
when we got it home we noticed that the upper radiator hose was leaking where it hooks to the engine. it had a new 'oldstyle clip' on it & the part of it attached to the radiator hadnt been removed.
we waited until the next morning to be sure the blazer started in the morning (our original problem). it started just fine on first crank, so i ran to the parts shop to get a new upper radiator hose with new screw-style clips. hubby puts it on showing me that there is rust on the old hose that wasnt cleaned off of where it attaches which made it not have a tight seal. he used some very fine sand paper to clean where the hose will go on & some vaseline to help slip the new hose on & so far no leaks.
he said the old hose was still in fairly good shape if it would have been cleaned when it was put back on.
he also found the bolts holding the fan shroud were all loose so he went through & tightened things. none of the parts on the engine had been cleaned so we are hoping that we wont have future problems due to them being removed & then not cleaned when replaced. But hey at least the blazer starts first time every time even if we did get a humongous bill from the dealer (lots of labor hours).
There is also a recall that is out that they fixed which I got a notice in the mail while it was in their shop for the switch for the brake lights/hazards or some such thing so keep an eye out if you havent gotten the notice.
Thanks for all the tips on the board. Hubby had thought that it was probably the screen in front of the fuel pump that was the problem, but he said if we replace that then have to replace the fuel pump too which means pulling the gas tank & he is having medical problems with his arm so it wasnt something he could have done. Overall we were happy with the dealer finding what we couldnt. The mechanic working on our blazer was really getting frustrated trying to find the starting issue too even with all their testing equipment & training so it didnt hurt my hubby's feelings too bad since he wasnt the only one that couldnt find right off what was causing the long cold cranking start problem.
Now if we could just figure out why my passenger door has a sound like there is something plasticloose in it.LOL

6/19/2008 ~ update ~ when they went to replacepartsthere was coolant instead of fuel so they are doing more testing & wont be getting it back today.

6/18/2008 ~ update ~ after three days at the dealer they finally have it narrowed down to two problems:need to replace fuel pressure regulator & spider assembly. it is supposed to be ready for me tomorrow so will let you know if this fixes the problem.

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Thanks for the suggestion. Frustration has taken over today so will check that out later. What happened to the good ole days when all it took was air, fuel & spark ~ no computer involved!

Replaced the alternator this afternoon because the bearing was making noise, but didnt seem to affect anything (fluctuating gas gauge & flickering to floorlight). Also changed some vacuum hoses just because they looked like they needed it(notexpecting it tohelp with starting issue).

Going to the dealer tomorrow for the fobs. The people who owned it before us said that they had a fob that didnt work & the dealer had told us that there were two of them & the easiest way to figure out which one was the right one for our Blazer was to have them calibrate the fob & if it didnt work to calibrate the other one. When doing google search it said that not having the remote synchronized could cause starting issues & would need to be redone to fix it. Since we dont have any fob, it is hard to know if this is an issue or not. However as many times as the battery has been disconnected (& even replaced) there hasnt been a problem with our radio which seems odd since it is supposed to have the theftlock.

So have a few questions for the dealer & to see if we can setup an appointment some morning when it can have set overnight so that they can test it at 'first crank'. When going through the dealer listing of things done over the life of this Blazer it does say that a previous owner was having trouble with crank when cold in the morning & the dealer's solution was that couldntrepeatproblem, which is true if this Blazer doesnt sit overnight from what we have found.

Thanks for replying!
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update ~ (Monday) went to start the Blazer this morning & it started on the second crank (unexpectedly unbelieveable!). Talked to the dealer when we got the fobs & they said no problem about dropping it off for a 'first crank' testing to be done the following morning, if needed. They said they couldnt give the code for the radio until it locked up so will wait to see if we need it or not. Their records showed the same as our dealer printout that it had a full inspection & oil change & lube done & checked for a cold cranking problem (unable to repeat so notfixed)at the other dealer a month ago. For now waiting to see if the cold cranking problem is still with us.