5.7 Vortec: Intermittant start failure.

TwistR

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I have a 96 K2500 5.7 Vortec that was running perfectly. However, for the past week, it starts up normally but when I try to start it when it's warm after it's been off for 5 mins, it won't fire, it just cranks. When I release the ignition it will fire and choke a little sometimes. I'm not touching the gas. I've found that to get it started, I have to press the gas to about 3/4 and then it will start to fire, sputter, then start. It will run rough, then hesitate if I hit the gas hard. After a while, no hesitation on the hitting the gas hard. It's back to running normally. It's almost like it's a flooded carb.

I replaced the fuel filter 6 months ago. The rest of the truck is original and it has about 160k miles on it. Does a fuel pump behave like this before it failsl sometimes? Injectors? I will be replacing the dist cap, rotor, wires and spark plugs in a month or so.

No codes. TIA.
 

east302

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I've found that to get it started, I have to press the gas to about 3/4 and then it will start to fire, sputter, then start. It will run rough, then hesitate if I hit the gas hard. After a while, no hesitation on the hitting the gas hard. It's back to running normally. It's almost like it's a flooded carb.

Holding the gas down is “clear flood” mode as it temporarily stops injector flow.

If you have a scanner, see what the engine coolant temperature sensor is reporting. It should be ambient when cold, 190-ish when hot.

A fuel pressure test wouldn’t hurt. Could be a leaking injector.
 

stutaeng

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Probably injectors and/or FPR leaking down after warm shutoff and flooding the engine. As @east302 pointed out, holding the gas down will clear the flood. Are they the original?

Pretty easy to diagnose FPR with a basic fuel pressure guage. Injectors need an injector balance test. Diagnose properly before changing it, and go with the MPFI upgrade unit.

Good luck.
 
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GoToGuy

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Have you done the injector spider conversion?
 

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