92 S10 Wont start if Key is fully engaged

Allright this is on my sons 92S-10 Blazer. Its the vortec engine and is a complete pain in my @$@$. The car seems to only get fuel when you try to start it by just bumping the starter over. If you try and crank it like a normal car it will just spin till the battery dies. If you bump it over gently it will start after about 5-6 hits. The blazer runs perfect after its started and does better on the warmer days. I have had tons of suggestions including the oil sensor, pressure regulator, fuel pump allowing the gas to flow back into the tank, the ignition switch, the key and on and on and on. You can prime it with gas and fires right up so if it was carburated I would simply look for a fuel issue but with all these damn sensors I'm lost. The boys needs his car back and it scares me financially to death to just drop it off at the local dealer. Any help would be greatly appreciated. Email me at [email protected]. The blazer is auto and 4X4, fuel injected. The only place I can find a fuel line is at the rear of the block on the drivers side where it appears to be where I would check the fuel pressure.

sounds like a fuel problem to me, the engine won't start with low pressure. start with the basics. what's the fuel pressure? rocking the ignition on and off restarts the fuel pump each time until you get enough fuel pressure to start. try changing the fuel filter first.

so what you are saying is that when you turn the key to on ( not start ) you cant hear the fuel pump prime ? check the solenoid on the firewall by the brake booster 1st - if that fails or the priming electrical circuit - the truck will start once the oil pressure hits 4 or 5 psi as the pump circuit is wired into the oil pressure switch as a safety - no oil pressure /no fuel save the engine from failure / but will let you start up when the priming circuit fails .