2004 trailblazer doesn't start on first try. It cranks and eventually starts but usually 3-6 tries. Once started it runs fine. I have no check engine light. We have replaced the spark plugs, b

you must RUN the SCANNER/computer for better diagnostic and fix it. YOu can have some faulty like: PCM+BCM+ignition coil, sensor, etc. see the diagram attached.
God bless you

If it cranks but does not start, the battery and starter are out of the picture.
Someone would need to check fuel pressure and for spark at the plugs to proceed.

That doesn't what ?????????????????????????

If Th engine doesn't crank have the battery and battery cables checked for condition and corrosion. If the engine cranks and dos not start then have the systems control computer scanned for fault codes and have the fuel pressure checked.

The creek? Sure sounds like it. Have a mechanic listen to the knocking. Rod bearings or crank main bearings may have gone out.

Possible fuel filter, fuel pump issue. Check out these items and let me know what you find.
I hope this info helps!~subyguru~

Try this first, and lets see what happens. Turn key to on, but not start, then off. do that about four or five times, then try to start. See if it starts, runs, then dies. Let me know. Have you had fuel pressure tested at all? If it doesn't start and run for a short while at least, take air intake hose off at throttle body intake, open throttle and spray a good shot of WD-40 into throttle body, then try to start. If it starts, you have a fuel delivery problem, maybe fuel pump or plugged filter would be first to check. Just because you hear the pump, doesn't necessarily mean it's getting proper pressure to run. Let me know what happens when you try this, and we'll go from there.

If battery and connections are good (it's a big draw,different then other components).Because a bad connection or old battery can sometimes work the starter after it sits,doesn't make it .Some times a starter has a bad spot,thats whe you see some one get under and directly jump it.If buying a battery get at least recommended cranking amp size battery,Larger auto stores check battery no charge (bad joke). Its free google /bing who does a free battery test.Auto zons,pep boys,sears.May even be running a sale.Most switch out battery for fee (no charge*),*Hopefully you will laugh later.

check fuel pressure, try cycling the key to the on position an couple of times not the start position to cycle the fuel pump then try to start it. could be the cold start circuit. once its warm does it start easy ?

fuel pump relay could be sticking, try touching it when the vehicle won't start, if it's overly hot try hanging it...