To start I have a 2000 2dr. 4x4 4.3L V6 W motor with 83000 mile almost. I've read many of these posts but none seam to have the same quirk as mine. One the colder it is the harder it starts, turn more slowly, and if i hook it up to a battery charger it will take right off almost instantly. It has a new batter that has been tested and it is good. New fuel filter didn't fix it or new spark plugs and wires. I also just changed the oil from 10w to 5w with not noticable change. And since the new plugs were installed the mileage drop from 18-20mpg on the highway to 14-16mpg. Wondering in single diget temps outside have any effect since this is my first winter without a diesel truck. Runs fine once started but will not start motor cold. Might be PCM since it had a dump truck roll into it. The worst damage is on the fender two dents that a covered by the bug gaurd above the headlight on the passanger side. That is when it all started to go wrong for my blazer. That should be everything.

I'm hoping to narrow down the list of things that could be the problem. So any help would be great.
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Start by checking all the battery cables and their connections, have the starter and alternator tested, and what type of spark plugs did you install and what did you set their gap at?

 

What kind of battery and what cold cranking amps does it have? Maybe you have too small of a battery. Also have that starter triple checked, and also triple check all the power and ground connections. When the truck is cold, it will need ALL the power it can get to crank over. And also, what brand of plugs, and what gap did you use, just like rriddle3 said. Also on your fuel economy, did you replace the cap and rotor? How about the air filter? Those two items can also cause low fuel economy. And one last thing..... Do you idle the truck more in the winter? If so that with the blend of fuel that they use in the winter, that also burns faster, so you use more of it, can also cause the drop in fuel economy. On my Blazer I lose about 50 to 70 miles per tank in the winter. HTH

 

The spark plugs a platinum tipped autolights with .060 gap. I have replaced the cap and rotor yet but meaning to. It warmed up to just under 50*F and the motor turns over just as fast as if it has the charger on it. However it still wouldn't start on the first try. Had to cycle the key to get it to start. On the second try it sputter then died and took off on the third try. I have checked and cleaned the battery cable connection every but the starter. The battery is 600 cca at 0*F.

To answer Kordog question about idle time I usually idle just long enough to get oil flowing, around 30-45 seconds. I going off of the instant mpg reading that it gives me so I need to check mileage at my next fill up. The drop in economy was instant once the plugs were in. The only other thing was that I changed was the motor oil and trans fluid. Just cleaned air filter and mass airfow sensor and found the intake was lose. Had a local mechanic do the work for me since I don't have a place to do all of this. He is pretty recomened around were I live and he done other work for my family without problems. So I'm going to test it again once that is done to see if it helps at all. Once that is done I'll share the results.
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Well to be honest, get rid of the Autolites, and get some AC Delcos in there. Also check the fuel pressure. The truck will crank slower in the cold, but what it is starting to sound like is your fuel pump is not suppling enough pressure. So try that and see what the results are. Let us know what the pressure is when you FIRST turn the key on after it sits, and then start to crank it, and then cycle the key again, and see what it is then. If the pressure is higher after the key is cycled then it probably is the fuel pump. These motors need allot of fuel pressure to start, and if it does not see 60-66 psi, then it will not start.

 

Alright put every thing back together and got a meager improvment in milage but still not where it was. Just shy of a hundred miles, 70% highway at between 60-65mph, and only 13.2mpg average according to the trip computer. To think I bought this Blazer because of the cost of fuel compared to my last diesel pick-up. Which would have been $75-$80 a week.

Don't really want to get a new set of plug so soon, only couple hundred miles on them. Never realized that brands where that much different, so much for the "premuim" spark plugs. Another thing about it starting is if it is warm it will start on the first try with no problems. I'll will still get myself a fuel pressure gauge tomarrow and then check it when it is cold. Which stores sell AC Delcos anyway never seem to find them.

Thanks for the help so far.
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Did the drop in mileage happen pretty close to the drop in outside temperatures? If so, it is possible that it is related to the cold weather formulation of your fuel. Being located in the northern half of the US, most all fuel forumlations are modified to aid in cold starting. All of my vehicles drop 2-4mpg in the winter.

 

So the mileage issue my not be that big of a problem, just don't want to wait till spring to find out if its temp/fuel related. This was the first real cold spell that i've had with since i got it in late feb. last year.

Would it also have happen because it wasn't pulling all of the air through the MAS. I didn't realize the air intake was loose at the throtle body until today. Once it warmed up completely it was only 2-3mpg less than normal. It like driving in four wheel drive but it's not.

When it was get better mileage and I was driving five miles to work, mostly inclines and accerating, it averaged 12.5mpg. Now i drive fourty miles one way to school 5 times a week again which did have it up to 17.5-18.5mpg. While everything was good.
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Sit. rep. on my blazer. Got the new distributer cap and rotor on. Finally checked fuel pressure turn the key on or off and it goes to around 58-60 psi. Then it slowly begins to drop with or without the key on. Still need to wait for it to completely cool off and check again. Engine temp was just above 100*F. The pressure at idle was 50-54 psi. Wish the gauge was fluid fill to reduce vibration it moves around pretty fast.

Milage problem fixed however. Need to clean my air filter more often and make sure the MAF is pluged in(huh).

Finally checked fuel pressure on a cold engine and only got ~55 psi.
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HI,
Have you found the cure?
I have the same problem with my blazer, 1995 vortex engine. I have replaced the spider injector, the plugs, wires, cap and rotor, bought the book and checked my pressure to the specs(fuel) I have 60 psi on "key on" and 53 psi when it is running. In the morning when it is cold it wiil not start. One quick spray of starting fluid in the intake and it takes right off and will start all day till next morning.