I have a 1999 S10 Blazer LS 4wd 4.3l V6 that I have slightly modified with an AEM Intake ( down pipe and cone filter ) and a Thrush Welded Muffler and turn down. My problem however has been occurring before I installed these things. Every morning ( and after it has sat for more than 4 or 5 hours ) it is very difficult to start. It seems even harder to start when it is cold. Sometimes it will run the battery down trying then as soon as I connect a jumper vehicle it will crank ok. Other times I can get it to crank on the third or fourth try. It has pressure to the rail (not sure how much) and I hear the fuel pump running when I cycle the key (and after a few cycles it wont run, making me think it has built up sufficient pressure stopping the pump, then will continue after a few non-successful tries at starting). It seems to be getting spark and I have changed the plugs and I hope to get wires and a cap and rotor soon. After I have driven it a mile or two it starts fine the rest of the day unless it sits too long. Please help me fix this without too many expensive tries!!!!!!!!!

 

Could it be a faulty temperature sensor? I had a Pontiac that was a real bear to get running after sitting a while but started/ran fine once it had been warmed up. Replaced the temp sensor (on block, not rad fan switch of course) made that problem go away.

 

I don't know much about anything newer than a 93, but it sounds exactly like a problem I had a couple of years ago, ended up being the fuel pump. You need to find out how much fuel pressure you have, it takes more pressure to start than it does to run.

 

Like ffox said check the fuel pressure....just because you can hear it does not always mean it is working "correctly".

After that check/clean the idle air control valve.

 

Thanks guys what sould the pressure be to the rail?

Also how could I check the temp sensors?

 

96+ Fuel System Diagnosis
I suspect a leaking fuel pressure regulator.