I have a 99 tahoe 5.7 ltr. with 177,000 miles on it. It has been hard to start lately I figured it was because of the cold weather. So I changed plugs, wires, caps, and fuel filter and still was hard to start. Did a fuel pressure check and it read 50psi so I figured the fuel pump is good. Then went out today and it started right up of course the tempture outside was 72. Forgot to mention that it has no power when driving it what I mean is that when you try to pass someone it hesitates.

 

sounds funny i would have some one out a scanner on it .

 

Might try running 2-3 bottles of Techron thru it.

 

I second the 2-3 bottles of Techron (all in the same tank) if it improves the starting and performance its probably time for injector servicing

 

Well guys it did the same thing started right and it was warm today. Took it got a scan on it found it saying that my O2 sensor is going out but my check engine light never came on saying anything. But would that cause the truck to not start in cold weather, but starts right up in warm weather like nothing is wrong and could it make it run that bad to, but i'm going to change it out and try again.

 

I don't think a bad O2 sensor would prevent starting since I think it starts in an open loop condition but that may just be the OBC I systems.

 

I'm thinking some form of fuel delivery, a cold start runs a little richer if I'm correct and a warm start not so.
have you tried cleaning up the throttle body?
the throttle plate could be staying open and causing the hard starts when its cold but not so much of an issue when its warmed up.
I'd check and make sure the throttle plate is completely closed with the engine off.
Check the plate screws make sure its not sloppy.
Check the linkage also.

 

You need to look at the coolant temperture sensor. It may be reading to warm when the truck is cold. In which case it maybe in closed loop instead of open which would give it the extra fuel it needs when it is cold

 

That is a good thought...