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Hello, my name is ***** ***** I am a professional here at Justanswer. Thank you for your question and I will assist you with your concern.If you are sure you have good spark to the spark plugs as well as proper fuel pressure and injector pulse have you removed the spark plugs and ran a complete engine compression test?
Okay if you install your fuel pressure gauge what is the fuel pressure reading while your adding fuel?
Okay so you have 38 PSI of fuel pressure good spark at the spark plugs and injector pulse then the engine should start and run on its own. Are you sure your injectors are firing?
Something dose not make sense here, you sya you have good spark and injector pulse and proper fuel pressure but yet it only runs with added fuel. Which indicates a fuel concern. Are you sure the fuel in the tank is okay?
Okay as I am sure you know it take good spark to the spark plugs, injector pulse at the injector , proper fuel pressure and good compression for the engine to start and run. If your 100% sure you have all of theses things the engine really should start and run.
If you getting 50 PSI that to much pressure, are you fouling the spark plugs?
Well in that case its not likely over fueling, if the only way you can get it to run is with added fuse then the engine is starving for gas.
Yes you are right on the 4.9 engine. The if your reading are correct then this is not the issue. You say it will only run if you add fuel . That tells me the engine is not getting gas. Im out of ideas at this point.
Are you getting 12 volts at the power feed wire (red)?
The injectors are controlled by the ground switching signal from the PCM and if the injector are spraying as you have stated then you have injector pulse.