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My 99 GMC Sierra (newer body) won't start in the morning (around 75 degrees F outside) but will in the afternoon (around 95 F outside). It cranks fine; just a fire, air, or fuel problem. Also, lately after startup it lags a little bit when accelerating, but after it warms up it runs fine.


   
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Location: Oregon
you should check your fuel pressure. it sounds like it may be below spec.
4.3l, 5.0l, 5.7l should be 60-66psi
4.8l, 5.3l, 6.0l, 7.4l should be 55-62psi

when it doesn't start in the morning, try cycling the key on two or three times before you start the engine. That is turn the key to the on position and you should hear the fuel pump circuit cycle. Do that two of three times then try to start the engine. This allows the fuel pump time to prime the fuel system and build up more pressure before you crank the engine.


   
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I change the coil on my 99 gmc today, runs fine now.


   
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