If you have the spider fuel system, I always check that first. That fuel system is noted for problems. In the past, I saw a service bulletin about hard to start after setting overnight. Once you got it started, it would do fine the rest of the day. The next morning, the same thing. The injector poppets were sticking after the vehicle set overnight. The fix was a cleaning procedure, the procedure I saw was a shop procedure.
I can't rule out moisture issue? Engine running, raise the hood in the dark, can you see fire running everywhere or jumping. Did you check for moisture in the dist cap?
Do you own a professional type scan tool that show's engine sensor data ?
048 Engine Hard to Start or No Start Scan Data for Starting Problems
003 Fuel System Tests Scan Data Tests
SOURCE: 1997 gmc sierra 1500 5.7 vortec got spark got fuel
You said you have fuel pressure but what is it? It has to be 55 psi or it won't even try.
SOURCE: Can a 1995 4.3l vortec v6 from a chevy astrovan
yes i imagine so. they are the same block but with different intakes.
SOURCE: 2006 gmc sierra 1500 stalled and will not start.
i have a 06 sierra that done the same thing and it was the distributer gear stripped
SOURCE: 2004 gmc 1500 sierra heater control stuck on
Defrost is the default position. Is the control a autyomatic temperture control unit? ( you set the temp and select automatic) if it is the system is completely electronic. You push the buttons and the control still says defrost or can you select something else and the control shows it but it just keeps coming out the defrost? If the control changes and the air comes out the defrost anyway and the cheack engine light isn't on, then the problem can be blown fuses or an air door actoater not working. Does the dash emit a clicking sound? if it does with the covers off the bottom of the dash reach around touching the different pieces till you touch the idem that is clicking. this is an acutor motor, or blend door motor. they have gears in them that wear out and break the motors aren't repairable and you just replace the ofending motor. the door that is moves can be stuck. and may have to be freed up with blaster, WD40, or other rust buster till it moves easy. maybe after getting the door to move smoothly you can get the old motor to move the door wiithout having to install a new one.
SOURCE: My 1990 GMC sierra pu dies randomly while driving
COULD BE BAD IGNITION COIL OR MODULE.IT COULD BE BAD FUEL INJECTOR OR INJECTORS.CLOGGED FUEL FILTER. A BAD DISTRIBUTOR CAP ROTOR + BAD PLUGS AND WIRES WILL CAUSE PROBLEMS AND BAD FUEL WITH WATER IN IT.
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