hard start

I have a 95 Blazer with 117K miles. I'm having problems starting it almost every day - I have to let it crank for 4-5 seconds before it will
start.
Interesting fact is that if it sits for a few days it will start right up as soon as the key is turned.
Replaced the fuel filter which did not help.
It gets pretty good gas mileage at 20 mpg highway.
Can someone please tell me with these symptoms where to look for the problem?

I had the same problem on my 99. My problem anded being the fuel pump. After driving and letting it sit for maybe 10-15 minutes it would take about 5 seconds of cranking to start. It got to the point where it just would not start at at. I checked for fuel pressue at the shrader valve and nothing. Checked for power to the fuel pump, good. So I plunked down $270 for a new pump and filter. Haven't had any problems since. I was acutally luck that it died altogether, because it had been being hard to start for about a month leasding up to the failure and I could never catch it when it was failed to do any testing.

So I would get a fuel pressue gauge and hook it up and see what kind of fuel pressure you have at the fuel rail.

I have the exact same problem with my 2000 Blazer. I've put in a new air filter, fuel filter, alternator, belt, and spark plugs, and run fuel injector cleaner. I guess I'll have to try a new fuel pump...

I have a 95 Blazer with 117K miles. I'm having problems starting it almost every day - I have to let it crank for 4-5 seconds before it will
start.
Interesting fact is that if it sits for a few days it will start right up as soon as the key is turned.
Replaced the fuel filter which did not help.
It gets pretty good gas mileage at 20 mpg highway.
Can someone please tell me with these symptoms where to look for the problem?

I am 80% sure you have a bad CPI fuel pressure regulator. Mine did that every once in a while and this fixed it.

You will need to swap out the fuel line kit and the whole CPI injections system.

Get the cpi injector off of ebay for US$200-US$250, get the nutkit at the dealer for 100 and replace it yourself.

The truck will run awesome after and you will pick up 3-4 mpg.

http://www.s10forum.com/forum/showthread.php?t=113559&highlight=cpi+replacement

What's the easiest way to diagnose if the problem is the fuel pump
assembly or the cpi/nut kit?
After it runs, it starts up immediately, but if it sits for 1/2 hour or more
it takes longer to start.

That's a Fuel Pressure regulator on the CPI injector going bad.

You need to hook up a fuel pressure gauge and turn the key to "ON", not start and see if it hold pressure at 60-62psi.