No matted if its hot or cold, wet or dry, day or nite my 2004 Suburban Z71 won't start on first try but always on the second bump. I replaced the ignition starter switch but no help. Any guess?

 

Check the fuel pressure, and go from there, and you don't have to press the gas pedal on the FI engines. It won't inject any more fuel if you do. Check your fuel pump and make sure it is working fine. If you have higher mileages, you may get carbon built up on the throttle body, so try to clean the throttle body and MAF Sensor.

 

Your problem is one of two things: fuel pressure regulator or fuel pump. Make proper diagnostics to know more

 

Check the flywheel also. I have the same problem with my 97 k1500 z71. I know my problem is the fly wheel

 

There is a fuel relay that can go bad and have that symptom too. Its the easiest to check out of all the proposed issues.

 

I have the same problem. I think it is fuel related because I can turn ignition switch to run and wait 5 to 10 seconds and then start and it will start most of the time. Not always.

 

It is the check valve in the fuel pump assembly. When they go bad the fuel flows back into the tank. You have to crank 5 to 10 seconds so the fuel pressure can build up again. I had that problem and put an inline check valve in the fuel line near the tank and no more problem. You can either change the fuel pump or add the check valve.