98' K-1500/350 vortec. rough startup/idle when eng. is warm

[FASTOYZ]

Hey everyone,

I'm having some issues with my truck that I cannot figure out to save my life. It is a 98' K-1500 silverado with a vortec 350. I have 106K miles on it. I've been having a problem during WARM startup. When you go to start the truck it will sputter,miss & run at about 200rpm for about 10-15 seconds, then the idle will come up to full idle at which point it will chug black smoke for a couple sec. as it seemingly cleans itself out after the rough start. Now here is where it gets interesting.

1. It never does this when the engine is cold, only when warm.

2. If you turn the key to on...wait for fuel pump to cycle then turn key to start it will start perfectly every time.

3. I had an in-line fuel press. test performed by Mr. goodwrench & results were 48-50 psi. This I am told is below normal (55-60).

So, it has to be fuel pump right? My cousin who is an ASE cert. mech helps me change my fuel pump & we install an aftermarket pump (much quieter) which I cannot remember the name of, starts with a W. Go to start the truck & the problem is still there... nothing has changed. So I change the fuel filter just to rule it out along with the throttle pos. sensor.

Now all this has happened about 3 months AFTER we did an intake manifold gasket change along with changing out the fuel injectors simply because of the amount of carbon buildup on them. Now I don't beat my truck but I don't drive it like a grandma either but these injectors were nasty looking. Any ways we put everything back together & all is well for like I said about 3 months or so & now the startup problems. The plugs, wires, cap , & rotor are all fairly new.

I appreciate any help/ideas as i have run out of ideas & have been forced to make an appointment at the dealer for this coming tuesday.

Thank you,

Chad

[BKLOSE]

Did you try the fuel pressure regulator??

[wct]

Did you try the fuel pressure regulator??

 

same suggestion what is your fuel pressure doing now? with key on engine off fuel pressure should hold around 55-60 psi if it bleeds down then it's probably a regulator

[RCH]

Have you checked the IAC? maybe it is sticking. (JAT)